Cornell Mniversity Library

THE GIFT OF

 

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THE DAILY MARCH OF TRANSPIRATION IN A
DESERT PERENNIAL

BY

EDITH BELLAMY SHREVE

 

WASHINGTON, D. C.
PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON

1914 a«
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CARNEGIE INSTITUTION OF WASHINGTON
Pusiication No. 194

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PRESS OF GIBSON BROTHERS, INC.
WASHINGTON, D. C.
Introduction....

CONTENTS.

Transpiration Studlesy gst wea es rineatns Gee AERA We ew ES EE TO

Methods....

POX Peri eN CALION 2,5. 25 foneis. <ichecelars a duslascuueaceas 4 teala a alee a Raglale ene amalacew eed

Observations
Discussion of

on transpiration experiments. .......... 0... c eee
transpiration experiments..............0e eee e eee eee ees

Experimentation v.25 asec cate ee auies aeons menrs dose eee eee ewes
Discussion of stomatal behavior. ......... cc ccc cece cence eee eens

Daily course of

water-content of leaves, twigs, and stems..................

EXpPerimMen tations... 6 acacedea gowns atide eee dace eee Rens

Discussion. .
Daily course of
Method.....

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Experimentation « ic suaiswwave et ealews als bee ha anda ped elk ea leno aes

Discussion. .

Daily course of transpiration under conditions of high and low evaporation. ...

Method ....

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Discussion...

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General summary
THE DAILY MARCH OF TRANSPIRATION IN A DESERT
PERENNIAL.

INTRODUCTION.

A consideration of the various types of perennial plants indigenous to the
vicinity of the Desert Laboratory at Tucson, Arizona, brings to view some
striking differences between the species concerned, in respect to their total
annual water-losses. The perennials fall into the general types, succulent
and non-succulent, the latter being easily classified further into three physio-
logical groups, namely: (1) small plants whose perennial parts are confined
to roots or underground stems; (2) plants continuously in leaf; (8) tropo-
phytic plants. Examples of the second class are Covillea tridentata, Lycium
berlandieri, Celtis crassifolia, Encelia farinosa, Hyptis emoryi; examples of
the third class are Prosopis velutina, Acacia greggii, Fouquieria splendens,
Jatropha cardiophylla, and Parkinsonia microphylla. The tropophytic
plants are alike in that they all drop their leaves more or less quickly in
times of drought, but Parkinsonia microphylla differs fromthe others in hav-
ing a continuous covering of epidermis over all of its parts, even the limbs
over 100 years old having an active chlorphyll layer covered with an
unbroken living epidermis. Thus, although the trees are without leaves
during times of drought, they must still lose a large quantity of water.
Some of the evergreen plants have a continuous epidermis, but these are all
_much smaller than Parkinsonia and hence expose a smaller evaporating
surface. In spite of this necessity for a large loss of water, Spalding*
calls Parkinsonia a “highly successful desert species, growing in abundance
and equally well on slopes of all exposures.” Shrevef found a high death-
rate in seedlings of Parkinsonia, but reached the conclusion that the critical
period in the life of the plant is over after the first two years.

The abundance of Parkinsonia on hillslopesin an arid region is an index of
its apparent success in spite of the exposure of a large evaporating surface
during the entire year and the difficulty its seedlings have during the first
two years. In consequence of the ability of Parkinsonia to overcome
these adverse conditions, it was selected as the subject of transpiration-
behavior studies. Ageneral study of transpiration behavior ofseedlings and
adult plants during different seasons of the year is in progress, but certain
fluctuations in the daily transpiration rate make a separate publication on
this phase of the work advisable. Only such description of the plant, its
habitat, and its anatomical features will be given as seems to apply either
directly or indirectly to the phase of transpiration mentioned.

 

*Spalding, V. M., Distribution and movements of desert plants, Carn. Inst. Wash.
Pub. 113, 1909.
{Shreve, F., Establishment behavior of palo verde, Plant World, vol. xrv, p. 294, 1911.

5
6 TRANSPIRATION IN A DESERT PERENNIAL.

The work is being carried on at the Desert Laboratory at Tucson, Arizona,
and is made possible through the kindness of Dr. D. T. MacDougal, who has
placed the facilities of the laboratory at the writer’s disposal.

Parkinsonia microphylla is a leguminous tree with minute deciduous
leaves. Plate IC shows the general appearance of the adult tree, while No.
4 of plate IB gives an idea of a seedling which has grown under natural con-
ditions for a year. No. 5 of the same figure is a seedling, about eight years
old, which was killed in transplanting. All adult trees in natural conditions
carry from one to eight dead limbs and have from 5 to 10 per cent of the
medium-sized branches dead; about 30 per cent of the twigs are dead-for a
distance of 2 to 5 em. from the ends, and after the first dry season succeeding
growth practically all twigs are dead for a distance of 0.2 to 0.5 cm. from the
ends. (See also Shreve, F., loc. cit.) The above is merely an estimate from
general observation and is not based on statistics.

The leaves appear in the late winter after the rains, are usually shed
during the arid fore-summer, reappear within a few days after the summer
rains begin, and persist for varying lengths of time, according to the amount
of rain falling during the early autumn. During the autumn of 1910 the
leaves had all fallen from the trees on Tumamoc Hill before the end of
September, but in 1912 many leaves persisted until killed by frost in January
of 1913. The rain records taken at the Desert Laboratory show a much
drier autumn for 1910 than for 1912. During both these years a tree near
the laboratory, where it probably received water from an artificial source,
retained its leaves until January.

Observation of the trees on Tumamoc Hill showed the following general
response to progressive desiccation of air and soil: First, the leaflets drop,
leaving the rachises still attached; then if no rain comes the rachises are
shed, and after a month or so the ends of the twigs die. All leaves do not
necessarily fall at once, for sometimes as many as half of the leaflets may
remain for a month after the others have fallen. These observations were
made throughout 1910 and the summer, autumn, and winter of 1912. At
the same time, observations were made on two plants which probably
received an abnormal supply of water. The first was a tree situated near
a south door of the laboratory, where its roots probably received a reserve
supply of water from beneath thelaboratory porch. This tree hashad no new
dead twigs or limbs for the last three years at least, and during those years
has retained its leaves from four to six weeks after the other trees were
bare. The second was a plant about 3 feet high, whose main trunk had
been cut off in the spring of 1909. Its root was thus unusually large in
proportion to its top, and it was otherwise under unnatural conditions, since
it was shaded by the laboratory during a large part of the day and the soil
about its roots was covered with a mulch of crushed stone. This plant
has lost no twigs or branches since the cutting took place and has leaves
throughout the year, except in mid-winter.

During the above period many trees were observed both on Tumamoe
Hill and on the foot-hills about Tucson for evidence of the place where dying
SHREVE PLATE 1

 

 

 

A. Parkinsonia microphylla, end branch of a tree.

B. Plants of Parkinsonia used in experiments VI-X. Counting from left to right, Nos. 1-3 were raised
in the green-house, Nos. 4-5 were grown under natural conditions having been transplanted to pots
a short time before the experiments. Nos. 1-4 are one year old. No. 5 is about eight years old.

C. Parkinsonia microphylla, adult tree.
 

 

  
INTRODUCTION. 7

begins. Chlorophyll is abundant in all parts of the bark, except at the
short base of the main trunk, so that the death of any part of the tree is
easily detected by a change in color of the bark from bright green to brown.
Certain dead twigs were marked, and in the following year the dead region
was found to have extended farther down the stem, but no case was observed
where dying had begun below the tip. After a limb is dead it is of course
impossible to tell the stages by which it died, but the number of dead twigs
and short dead branches existing on live branches makes it seem probable
that death begins at the tips and progresses down the stem gradually. The
death of an entire limb seems in no way to affect the health of the plant as
a whole.

As is the case with most of the Leguminose, the plant possesses leaf-'
movements. During darkness the leaflets are ‘“‘ closed’’— that is, they stand
with their dorsal surfaces in parallel planes about 0.1 cm. apart—and with
the coming of daylight the leaflets separate, making various angles with the
rachis, the “wide-open” position being when the leaflets lie in the same
plane on opposite sides of the rachis. During cool or moist seasons the
leaflets remain ‘‘open”’ or partly open during the day, but during the dry
seasons of spring and fall they close within half an hour after sunrise and
remain in this position all day, sometimes opening for about half an hour
near sunset. Leaflets from potted plants that have been well watered open
wider as a rule in the morning than do those from adult trees and are slower
in closing. If, however, the potted plants are not given water for several
days the movements are more like those of the leaflets of adult trees.

The size of leaflets varies, both in area and thickness, with the age of the
plant and with the soil and atmospheric conditions existing during the period
of their growth. On seedlings from one to eight years old the area of one
side of a leaflet averages 0.04 sq. cm.; on an adult tree the average is 0.02
sq. cm.; and on hot-house-grown seedlings a year old itis0.06sq.cm. The
leaflets which come from very small branches emanating from the main
trunk near the base are frequently about the same size as those on young
plants. The diameters are approximately in inverse ratio to the area.
Figure 1 shows the diameters and arrangement of tissue in leaves of dif-
ferent types. The different drawings are on the same scale and were made
with a camera lucida.

The following differences of structure may be concerned with the trans-
piration studies which follow. The section of the leaflet from an adult tree
(A, fig. 1) shows large epidermal cells with heavily thickened walls, stomata
about midway down the first row of cells, very few intercellular spaces, palisade
cells and stomata on both sides of the leaf. The section from a plant grown
all its life in the green-house (C, fig. 1) shows no thickening of the epidermal
cells, many large intercellular spaces, palisade cells on the dorsal side only, and
stomataonbothsides. Thesectionfromtheleaf grownin the green-housefor
a yearand then placed out of doors for six weeks (B, fig. 1) showsastructurein
several ways intermediate between the other two. The epidermal cells are
thickened nearly as much as in the section from the adult tree; palisade cells
8 TRANSPIRATION IN A DESERT PERENNIAL.

occur on one side only, stomata on both sides, and the intercellularspacesare
fewer and smaller than onthe plant kept in the green-house all its life, but are
larger and morefrequentthanontheonefromthetree. Thesectionfrom the
twig of thetree (D, fig. 1) shows epidermal cells with heavily thickened walls,
from three to four subepidermal cells with walls very heavily thickened, sto-
mata sunken into the first andsecond layers of subepidermal cells, and guard
cells of thestomata covered withaheavy layerof cuticle. The sectionfroma

 

Fra. 1.—Camera lucida drawings of leaf and stem sections of Parkin-
sonia microphylla.

Cross-section of leaflet from adult tree. __

Cross-section of leaflet from plant grown in green-house for a year and then
placed in the open for 6 weeks.

Cross-section of leaflet from plant kept in green-house all of its life.

Tangential section of epidermis of twig from adult tree.

Tangential section of twig from hot-house-grown plant.

Cross-section of stoma from rachis of adult tree.

. Surface view ot stoma from leaflet of adult tree.

. Stomata from leaflets showing various apertures.

RABESQ we

twig of a green-house-grown plant (Z, fig. 1) shows epidermal cells thickened A
but there arenosubepidermal cellsand the intercellular spaces are larger and
more frequent thanin thesectionfromthetree. Anexamination of many sec-
tions showed that the stomata of the rachis are sunken slightly (F, fig. 1)—
that is, that they appear alwaysnear the base of the epidermal cells, that the
stomata of the leaflet itself sometimes appear near the bottom of this la er,
but that the usual place is near the top of the layer, and that the stomata of
the branches are always sunken below the layer of epidermal cells.
TRANSPIRATION STUDIES. 9

In general it may be said that the evaporating surfaces, both external and
internal, are largest in the plant which has carried on its entire development
in the green-house, next in the plant which has been in the green-house for
one year after germination, then in the open for six weeks, and least in the
adult tree. Of the different parts of the tree examined, the leaflets lose
water by evaporation most easily, the rachises next, and the branches least
easily.

TRANSPIRATION STUDIES.

METHODS.

The best method yet devised for measuring transpiration is doubtless
the determination, by weighing, of losses sustained by sealed potted plants.
In the case of Parkinsonia this method was not practical, since the plants
raised in the green-house differ from those growing in the open, both in leaf-
structure and in the size of stems and leaves. The influence of the two
environments on the size of seedlings is shown in plate I B and on the size
and structure of the leaves in figure 1. It proved almost impossible to
transfer small seedlings from their natural position in the ground to pots,
there being only onesurvival outof some thirty which were transplanted. It
thus seemed necessary to use a method for the measurement of water-loss
in situ. Cannon’s method" is adequate for a rough estimate of comparative
water loss from different plants under similar conditions, and seems to have
several advantages over Stahl’st method, yet for the purposes of the present
study, which require accurate quantitative measurements of water loss
under natural conditions, a more accurate method had to be sought. The
older methods, based on the absorption of moisture by means of sulphuric
acid or calcium chloride, have many of the same objections as the polymeter
method, ?. e., the plant, is not under normal conditions of humidity, wind,
and sunshine; moreover, the gain in weight of the absorbing material may
not represent the actual amount of water given off by the plant, but is
equal to this amount plus or minus the loss or gain of moisture in the air of
the bell-jar during the experiment. If the bell-jar is a large one and the
part of the plant under the jar is losing a small amount of water, this error
may amount to as much as 100 per cent.

A method was finally worked out which contains some of the features of
both Cannon’s method and the absorption methods. By a reference to fig.
2 it will be seen that the plant or part of the plant to be measured passes
through a platform and is covered by a bell-jar, within which are an open
dish of calcium chloride, a maximum thermometer, and a dew-point appa-
ratus, the last being so arranged that the dew-point within the jar may be
taken without any disturbance of the conditions within the jar.

 

*Cannon, W. A., A new method of studying the transpiration of plants in place, Bull.
Torr. Club, vol. xxx11, p. 515. a .

{Stahl, E., Einige Versuche tiber Transpiration und Assimilation, Bot. Zeit., 111, p. 117,
1894.
10 TRANSPIRATION IN A DESERT PERENNIAL.

The details of the platform are shown in Boffig.2. The groove seen there
was filled with mercury and thus an air-tight joint was made possible. In
the earlier experiments this groove was not used, but the bell-jar was sealed
to the platform with plastocene. The mercury seal proved to be a great
improvement with respect to speed of operation and the certainty of
securing an air-tight joint. The surface of the platform was made non-
absorbent by some 15 coats of shellac. The part of the plant to be used
was led into the platform through a small hole in a rubber stopper which
fitted tightly into the circular hole. The stopper was flush with the bottom
of the groove, so that mercury could pass over the joint.

 

 

 

 

 

 

  

 

 

Win

Fic. 2.—A. Apparatus used for measuring transpiration in situ.
B. Details of the base used in A.
C and D. Forms of atmometers used in A.

 

 

 

 

 

The dew-point apparatus was made for the purpose and is a modification
of Allouard’s form. It consists of a metal cube 2 em.on a side, one face of
which is accurately planed, nickeled, and highly polished. Close to, but insu-
lated from this face, is a polished metal flange for comparison. Into the
metal cube is fastened a glass tube of about 1.5 cm. diameter, which passes
through a rubber stopper in the top of the jar, the tube being long enough so
that the metal cube may be placed at any desired height within the jar.
From the top of the jar project a 0.1 degree certified thermometer and the
tubes necessary for the entrance and exit of ether. The ether was con-
ducted through a rubber tube about 15 feet long before it was allowed to
escape into the air. In the experiments carried on in 1911 ether was
TRANSPIRATION STUDIES. 11

used to cool the metal surface, but in 1912 carbon dioxide* was led into
the tube from a high-pressure tank. By this means the dew-point was
obtained much more quickly than with ether and the danger of physiological
disturbances caused by waste ether was avoided. Frequent tests with
this dew-point apparatus showed that the temperature of appearance and
disappearance of moisture differed less than 0.1° C. when the temperatures
were above —4° and not more than 0.2 degree when the temperatures were
below —4°,

The calcium chloride was exposed in shallow weighing-botitles, the covers
of which were air-tight when thesalt was not in use. Merck’sC. P. calcium
chloride was used, but to guard against the absorption of an appreciable
amount of carbon dioxide from the air by traces of potassium hydroxide
which might be present, carbon dioxide gas was made from calcium carbo-
nate and sulphuric acid, and passed dry through the calcium chloride until
saturation resulted.

Finally the entire jar was shaded, except a small opening which alloweda
beam of light to fall on the whole plant. Constant illumination was main-
tained by changing the position of the opening every 10 minutes, so that no
shadow ever fell on the plant. By this method of shading it was found easy
to keep the temperature of the air within the bell-jar within one or two
degrees of that on the outside, provided the volume of the jar was at least
1,000 times that of the plant and the jar was opened and fresh air let in
every two hours.

The amount of water given off by the plant was found from the gain
in weight of the calcium chloride plus or minus a correction ascertained
in the following way. The dew-point was taken at the beginning and at the
end of the period and from the Smithsonian tables the weight of water in a
cubic meter of saturated air at the temperature of the two dew-points was
found. The difference between these two weights was then multiplied by
the volume of the jar, proper corrections being made for the space occupied
by the objects under the jar. Corrections for altitude were made in a few
cases where the error from neglecting the correction amounted to more
than 0.001 gm.

The following conditions are provided in the present method: (1f Bie,
water lost by the plant can be measured accurately to milligrams by means
of well-constructed weighing-bottles and an accurate dew-point apparatus;
(2) the duration of the experiment may be from 15 minutes to 2 hours;
(3) transpiration readings in sunlight may be obtained by means of a special
method of shading; (4) the air temperature and humidity within the jar
may be made to closely approximate the condition of the outside air by a
proper manipulation of the shading device and of the amount of calcium
chloride exposed; (5) the influence of air currents can not be measured.

In order to measure the evaporation rate of a less complex surface under
similar conditions and thus to secure data regarding the behavior of the
plant itself, a second bell-jar was set up, identical with the first one, except

 

* The use of carbon dioxide as a cooling agent was suggested by Dr. B. E. Livingston.
12 TRANSPIRATION IN A DESERT PERENNIAL.

that the plant was replaced by a small atmometer which lost about the
same amount of water as the plant. This atmometer (D, fig. 2) consisted
of a tube containing a wick which dipped below into a small reservoir of
water and ended above in sand, slightly piled. A cover was provided for
the evaporating surface for use when the atmometer was removed to be
weighed. This atmometer was standardized to an open pan of water in a
dark room and its loss reduced to loss per square centimeter of water surface.
The results of this standardization brought out the fact that the atmometer’s
rate was a fairly constant one under the same conditions; for the average of
three readings of 24 hours each it varied lessthan 1 per cent from the extreme
readings. The actual losses from the atmometer during the experiments
were always reduced to unit area and the loss per unit area from the plant
for the same period was divided by this number, the result being called the
relative transpiration.* It might seem on a priori grounds that the shape
of the curve obtained from these results would be parallel to a true curve,
but that the actual values might be either too high or too low, since the
conditions under the two bell-jars were seldom absolutely identical; yet
the values for relative transpiration obtained in 1912, when atmometer and
plant were under the same bell-jar, are in such close agreement with these
earlier ones that the results obtained by the use of two bell-jars are shown
to be as accurate as are those obtained when one jar was used.

While this last method has the advantage over the earlier one that plant
and atmometer are under identical conditions, it has the disadvantage that
a larger beam of light must be let into the jar, with the consequent greater
rise in temperature within the jar. It will be seen, from the tables of
September 1912, that the temperatures under the bell-jar rose every day
as much as 3° above the outside air temperatures. Asin the case of humidi-
ties, it is true here that the plant is not placed under unusual conditions,
unless by chance the hottest day of the year was selected for the experiment,
and this was not the case. Yet, when only parts of a plant are used, it seems
best that the conditions surrounding the branch under experimentation
should be as nearly as possible identical with those around the rest of the
tree. In the subsequent tables, temperatures and humidities are given in
order that any difference may appear which might affect conclusions. A
number of experiments were discarded where the meteorological conditions
within and without the bell-jar differed over 10 per cent; but no experi-
ments were discarded which might bring out negative evidence for the main
conclusion.

Great care was taken to have all joints tight during the experiment and to
keep the weighing-bottles and atmometer air-tight when not under the bell-
jar. Before each set of experiments trials were made in which the atmom-
eter was used as a plant and its losses determined by weight and compared
with the gain in weight of the calcium chloride plus or minus the correction
determined from the dew-points. Sensitive chemical balances were used,
but readings were taken only to 1 mg. and the error taken as plus or minus

 

*Livingston, B. E., Carn. Inst. Wash. Pub. 50.
TRANSPIRATION STUDIES. 13

0.5 mg. In the final results no important conclusions are drawn from
numbers obtained from differences in weighings smaller than 10 mg.

The curves are all drawn to a scale which shows only readings which are
surely significant and well out of the range of experimental error. The solid
horizontal lines show the actual time and duration of the intervals measured
and the broken lines connect the mid-points of these. This scheme is used
because the irregularity of the time required for taking the dew-points made
_.it impossible to take readings at stated intervals. The time was always
read to the nearest minute and the hourly rate calculated. It will be noted
that the experiments made in 1912 show a greater agreement in the time
of readings, an advantage gained by the use of the carbon dioxide for cooling
the dew-point apparatus.

The extremely small size of the leaves prevented the use of any of the usual
methods for determining their area, and so a direct method was used as
follows. From 10 to 20 leaflets of approximately the same size were taken
at a time, placed carefully with their long diameters in a straight line, and
their aggregate length read to0.1mm. These leaflets were then turned so
that their short diameters could be measured in the same way. All of the
leaflets used in an experiment were thus measured and the average long
and short diameters were found. The leaflets were then treated as ellipses,
which they are so far as the eye can tell. The area of an average leaflet
was calculated and was then multiplied by the total number of leaflets. The
rachises were placed end to end and their total length was read. Their
average diameter was found from many readings with a vernier caliper.
The rachises were treated as cylinders, the groove which exists along the
top beingignored. The stems were treated in the same way as the rachises,
readings of diameters in this case being taken at regular intervals of 1 cm.,
as closely as the presence of thorns and branches would permit. Live thorns
were treated as branches and all dead ends of branches were left out of
account. Small errors doubtless occur in the operation of this method,
but the consistency of the results goes to show that the errors may be
disregarded and that the areas determined are comparable.

For the sake of comparison, plants raised in the green-house from seeds
and then placed in the open for six weeks were sealed in their pots and their
water loss was determined by weighings. The evaporation rates in these
cases were determined by the Livingston type of atmometer.* Atmometers
which had been standardized under Dr. Livingston’s direction were used
and the proper corrections for reduction were made by using the coefficients
furnished by him. The rates were reduced to unit area of water-surface
in order that the relative rates might be compared with those obtained from
trees by the bell-jar method. This standardization was done in a dark
constant-temperature room, an open petri dish, with a reservoir to keep the
water level constant, being employed. Two of the cups were run with an
open dish in this manner and the other cups were reduced to the open-
water equivalents by the use of the coefficients referred to above.

 

*Livingston, B. E., Carn. Inst. Wash. Pub. 50.
14 TRANSPIRATION IN A DESERT PERENNIAL.

Unless the plants have some special physiological response to wind action
the relative transpiration rates of potted plants ought to be comparable to
the relative rates of the plants taken in situ in still air. A general observa-
tional record of wind velocity was kept and it was found that whileamarked
increase in wind velocity was always accompanied by an increase in the
actual transpiration rate, this increase did not appear in the relative trans-
piration, thus showing that the plant was affected in the same manner as
the atmometer. The few conclusions drawn in this paper from a compari-
son of the relative rates of plants in situ with potted plants are of course
open to the objection that there may exist an unknown physiological re-
sponse on the part of the plant to wind which did not appear.

EXPERIMENTATION.

All of the plants or branches used in the following experiments were in
normal condition and were situated in exposed positions, so that the sun
could fall upon them the entire day. Whenever over-night readings were
taken the jar was completely covered with a black cloth. It will be seen
that, as the experiments progress in chronological order, the agreement of
meteorological conditions of the jars with each other and with the outside
become better, due to the growing experience of the operator. A small
amount of calcium chloride was exposed for the night readings, the amount
being about tripled for the first reading in sunshine and then increased grad-
ually as the day advanced and decreased in proportion as the afternoon
progressed. In all cases it was necessary to spend one or two days in trials
before the amount could be properly adjusted for a particular plant. Also,
it frequently became necessary to take into account the changes of dew-
point in the outside air. With the temperature kept within a degree or two
of that of the outside air by means of the method of shading mentioned |
above, and with the dew-point held near that of the outside air, the humidity
varied only a small percentage from the atmospheric humidity. In no case
were the differences between bell-jar and air conditions greater than the
differences existing between the atmospheric conditions of any two days.
Thebestresults were obtained when periods of one to two hours were used;
in the long over-night periods results were never satisfactory. Of course
two-hour periods might have been used at night as easily as in the day, if
the purposes of the experiment had required it. It was thought advisable
to eliminate so variable a factor as the wind and so no attempt was made to
get readings in the wind except in the case of potted plants.

In the tables which follow, unless otherwise defined, T represents the
transpiration rate per hour per square centimeter of area; EF the evapora-
tion per hour per square centimeter; and 7'/E the relative rate. All losses
are given in fractions of agram. Unless stated otherwise all readings were
taken in bright sunshine. In table 1, the original readings and some of the
details of calculation are given, while for economy of space these details are
omitted in the succeeding tables.

EXPERIMENT I.

The subject of this experiment was a small 1910 leafless seedling, growing

on the north slope of Tumamoc Hill. The area was found to be 7.99 sq. em.
TRANSPIRATION STUDIES.

Taste 1.—Transpiration of a leafless seedling (A).

Experiment I.

15

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Gain in| L
weight Loss per | */088 Per
Dat Ti Dew- a Correc- eg ne Le Pot Ti pour hee T
Bes ime. | point. aac tion, | from |- from {4 te Ame: attenea atmom-| FE
chlo- plant. | plant. v Stars eter.
ride. E
Mar 5,.| 5000 “Sa \ 440
ar.0.. yop.m. a ropn.m.
Mar 7) 600 pcan |—10'§ |10-111 |-0.057 | 0.054 | 0.0041 | 0.00052 tei pn }o.0088 0.007 | 0.077
700 a.m 5.8 645 a.m.
Zoy am) §.8)) oss |— oz} .036| .os2 | .oogos j{ 8 43 am! ox | 019 | .213
835 a.m.| 7.0 8 30 a.m. s
33 2] 791} oor] 000} 01] .045 | 00503 {46 $2 8™-)) og | 025 | .162
10 $5 am.) 7-0 j} .058 |— .005 | .083,] .025 | .ooste |(44 9g 3m) .065 | .052 | .061
150 pmJj 2.9 |) 145 p.m. 7
360 p.m} 6.0 f -038 1+ .013 | .046 | .023 | 00288 fe Be Lael 050 .040 | 672
Dew-point. Temperature. Humidity.
Date. Time.
Piané. | ACO | Ate, Blank [OURO ate, | Blank, | AERO) ae,
1911. °C. °C. oc. | op | °F. | °F. | pct. | pict. | pct.
Mar. 6.. 5h 00" p.m. 6.4 6.4 6.4 | 62 62 63 51 51 51
Mar.7..| 6 00 a.m.| —10.5 | —8.0 7.2 | 43 43 43 27 < 34 80
; 00 a.m. 5.8 5.8 5.8 | 54 54 54 64 64 64
8 07 am. 3.0 3.3 6.7 | 72 72 71 30 30 38
8 35 am. 7.0 7.0 7.0 | 76 76 76 35 35 35
10 35 am. 7.0 TA 7.0 | 81 81 80 28 28 28
10 55 a.m. 7.0 7.0 7.0 | 80 80 80 28 28 28
1 00 p.m. 5.9 6.0 40 | 84 84 83 24 24 22
1 50 p.m. 2.9 2.9 2.9 | 84 84 84 18 18 18
3 50 p.m. 6.0 5.8 6.0 | 82 81 80 25 25 25
20 BO
Pa sng,
IP ye
aot © Pa Sty
e we ihe sei .
Cie LUA
054
00
06} -
05t ge ae
045 ee ¢ pa ee
.03F ae
02 op a
01 gee
.00
006
005 Pa
a ‘
004 =o x
-003 a“ ST oa Se im ag
002; 7 vo
Z
x
ook”
fie
5 6 7 8&8 9 0 HW @ 1 2 8 4
Fia. 3.—Graphs for transpiration of A, a small leafless seedling. Exp. I.

 

 

 

 

 

 
16 TRANSPIRATION IN A DESERT PERENNIAL.

EXPERIMENT II.

Subject, a small leafless plant growing near the subject of experiment I.
Area, 35.65 sq. cm. Age, approximately six to ten years.

TaBLE 2.—Transpiration of a leafless seedling (B). Experiment II.

 

 

  
    
   
    
   

 

 

 

 

 

 

 

 

 

 

Date. Time. T Date. Time. E z
Mant 5h 18 Mar. 7 5b 20m 0.034
ar. 7... a yess hnclyvcnavetacoived any Tax PM eAviccovivaninaes ;
Mar. 8...) 6 07 a.m. ‘f| 9-00022 | Mar. 8..| 6 10 am } p nobad
6 52 am. 065
753 am. -00073 0111
8 05 am... 136
11 40 am)... 00454 ees
12 00 102
2 10 00539 .0525
2 50 s 066
4 50 -00252 .0382
Be 20: DAMMiinceivasnsarevarecaen deers = 039
Mar. 9... 6 20 a.m.............. 00025 Mar. 9.. 00686
6 55 am.........eeeee -106
755 am... 00148 Ohgs
8 05. Atlee coarse wien «120
10 05 am......... 00 00412 sate
10525 aM as sons, 101
12 25 pm... Oosrs ae
122250) (peIM csisistonitivecennte 094
2: 260° PM vavwwininnge rasan 200485 0517
3 22 p.m.............. 064
5 20 pm............, 200188 A081G
Dew-point. Temperature. Relative humidity.
Date. Time.
Plant.| Atmom- | air, |Plant.| Atmom- | air |Ptant.| Atmom- | air,
1911. °C, “CO, EO: oF one, °F. | p. ct. p. ct, p. ct.
Mar. 7...| 5h18™p.m...... 2.5 2.5 2.5 67 67 67 ve % ise
Mar. 8...; 6 07 a.m...... —6.5 -—1.0 3.0 48 48 48 32 49 67
6 52 am...... 3.5 3.5 3.5 52 52 52 60 60 60
7 53 am...... s 5.5 4.3 60 166 60 44 41 48
8 05 am 25.5 4.5 62 270 62 44 37 44
11 40 14.0 7.0 84 84 82 46 40 28
12 00 6.5 6.5 82 386 82 25 23 25
2 10 —6.5 5.8 90 90 87 7 8 21
2 50 al Bed 5.1 5.1 84 84 84 22 22 22
4 50 —0.3 —0.5 5.1 78 78 76 19 7 29
5 20 4.0 4.0 4.0 78 78 78 da on
Mar. 9...) 6 20 | —3.5 —1.0 2.5 56 56 56 aes ris ae
6 55 2.2 2.2 2.2 56 56 56 47 47 47
7 55 7.8 3.5 3.5 7 7i* 70 40 30* 29
8 05 3.5 3.5 3.5 72 72 72 29 29 29
10 05 12.0 11.7 6.0 85 84 84 36 35 24
10 25 6.2 6.2 6.2 86 86 86 20 20 20
12 25 14.5 13.8 6.0 95 96 93 29 27 18
12 50 p. 1.8 1.8 1.8 94 94 94 12 12 12
2 50 p.m...... —2.2 —2.0 1.8 96 94 93 9 9 13
3 22 p.m...... 1.8 1.8 1.8 92 92 92 14 14 14
5 20 p.m...... 3.0 3.0 3.2 78 79 76 24 22 25

 

 

 

 

 

 

 

 

 

 

 

 

 

18h 10" a.m. 28h 35™ a.m. 312b 25" p.m.
TRANSPIRATION STUDIES.

 

 

 

 

 

5+
: atten,
ger Oras ee,
ee i
7 | oo,
ed |
_—_
L -
: Ss Ba
a ; .
. on 8
ae ——
=e |
7
.03 J |
nee |
ge |
ee |
E = ,
sal een x.
-—————
| Sa
005 F = /
Fe .
vg
oe
so ;
| s
" Ry
aaa Telahieal
at |
| XN
“ |
‘
e dl |
; | | x
Le | 1 1 1 1 w+

 

6 7 8 9 0 11 12 1 2 3 4 5

Fic. 4.—Graphs for transpiration of B, a small leafless seedling,
March 8. Exp. II.

 

 

 

 

 

 

eerie So tcee
10 T ae yee Ad PS oss SPFERGs Receee eee
Ben 7,
05+ .
se
055 sgssene oe
en ys
ei ~S
03 “ :
m 4
at
i
7
sage
O1F EE L--"
[ges
005+ eee
ase Sie
# “Me
003 f Re
Wf ms a
‘ a aan
st
| a a
7 9 rr 1 3 B

Fig. 5.—Graphs for transpiration of B, March 9. Exp. II.

17
18 TRANSPIRATION IN A DESERT PERENNIAL.

Experiments III ro V.

The subject of these experiments was an adult tree designated C, about
20 feet high, growing southwest of the laboratory in an exposed place.
Three separate small branches were used, branch c being without leaves,
while d and e had a normal number of healthy leaves. The areas were:
c, 35.47 sq. cm.; d, 18.13 sq. cm.; e, 8.20 sq. cm. The platform was used
as before, but was mounted on a framework arranged to support the jar, etc.
The leaves on the tree were always completely closed before the readings
were begun.

TaBLe 3.—Transpiration of a leafless branch (c) of an adult tree. Experiment IIT.

 

 

     

 

Date. Time. T Date. Time. E z

1911.

Mar. 11...) 54 20™p.m. Mar. 11...) 5515™p.m.............

Mar. 12.... 6 45 a.m... “i 0.00031 Mar. 12...) 6 55 a.m. } 0.006 0.049
1 ees) couae 0S a O15) 14
See Se }} 00875 oy te “Vo os8 | ast
9 55 am 9 50 am
11 00 am?.! cc}) 00808 11 10 a.m pA | ete
11 25 am... “t 11 35 am
12 35 p.m... -) 00338 12 45 p.m 049 068
a ty bees }) .o0380 a 050 | .075
oe sty) 00292 aa 047 062
28 Bam) 00380 i i 029 | 088
5 15 p.m... aes 5 10

Mar. 13... 7 25 am... a, -00019 |] Mar. 13...]. 7 30 -0071 | .026
ie oe: ey 00354 co 022 158
9 30 am... wets 9 35
1088 ome) oon 10 50 oe?) cab Sau
ap eel amnell 1 044 | 069
200 bam ccc) -90a82 1 $3 019 | .078
fy ee ee) oar a 044 | .063
3 45 p.m... . 3 50 a
4 45 p.m } -00330 4 30 .053 062

 

 

 

 

 

 

 

 

 

 

 
TRANSPIRATION STUDIES.

Taste 3—Continued.

19

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dew-point. Temperature. Relative humidity.
Date. Time.
Plant. | Atmom-| air, | Plant. | Atmom- | air, [Plant.| Atmom- | gir.
1911, &6. Oe ae oF. °F, °F. ee, Pott. | pack.
Mar. 11..| 5h 20™p.m...| —3.5 —3.5 —3.5 59 59 59 28 28 28
Mar. 12..) 6 45 am...| —7.5 —7.A4 —1.5 40 42 40 40 37 65
7 20 am... —2.0 —2.0 —2.0 42 42 42 57 57 57
7 55 a.m... 3.0 2.5 1.5 58 56 56 47 49 37
8 33 am...| —1.0 —-1.0 —1.0 78 77 78 18 17 18
9 30 am...) —1.5 —2.0 —1.5 80 81 80 15 14 15
9 55 am...) —1.5 -1.5 —1.5 80 80 80 15 15: 15
11 00 am...| —3.0 2.5 —3.0 85 85 83 12 12 14
11 25 am...| —3.0 —3.0 —3.0 84 84 84 12 12 12
12 35 p.m...| —5.5 —4.8 —6.0 84 85 84 10 ll 9
110 pm...) —7.0 —7.0 —7.0 85 85 85 9 9 9
210 pm...) —4.5 5.5 —7.0 89 88 87 9 9 9
2 30 pm...) —7.5 —7.5 —7.5 86 86 86 9 9 9
3 30 p.m...) —7.5 ~6.5 4.5 86 86 84 9 9 9
3°45 p.m...) —4.5 —4.5 —4.5 82 82 82 10 10 10
4 45 p.m...| —8.0 7.5 —3.0 80 80 78 9 9 15
5 15 p.m...) —3.0 —3.0 —3.0 72 72 72 18 18 18
Mar. 18..| 7 25 a.m...| —1.3 —3.0 2.8 60 60 58 32 28 45
8 05 am... 2.0 2.0 2.0 60 59 60 41 42 41
9 25 am... 7.0 6.0 1.0 70 68 70 40 40 27
9 30 am... 0.8 0.8 0.8 70 70 70 27 27 27
10 55 a.m...| —5.0 —4.5 0.6 79 80 79 13 12 20
11 15 am... 0.5 0.5 0.5 81 81 81 18 18 18
12 35 p.m...| —5.0 —4.8 —1.8 85 85 83 10 9 14
1 00 p.m...| —2.0 —2.0 —2.0 84 84 84 13 13 13
2 00 p.m...) —5.0 —5.2 —3.0 90 90 89 9 9 10
2 20 p.m...| —3.0 —3.0 —3.0 90 90 90 10 10 10
3 20 p.m...| —7.0 —5.5 2.5 85 87 85 9 9 12
3 45 p.m...) —0.5| —0.5 —0.5 79 79 79 18 18 18
4 45 p.m...| —3.5 —5.0 1.0 82 80 76 13 12 22
BR eet Wee :
5 ao Tses0,,
E Mag aed eee a
055 oc ~
05} Se eee
Se x
ie Se
.08F E it —
ye *
a %
Zz N
+ \
.O1F ae ‘
fi ge ‘pas
/ \,
005 i
/ \ %
, \ s
‘ ‘ SS
a eigeas = tS
a
.003F ae ee
+ x
a ‘
4 ‘
s ‘
oof T ,” \
¢ 1 1 4 z i 4 rs Ss
7 9 1 3 5

Fic. 6.—Graphs for transpiration of c, leafless branch of an

adult tree, March 12. Exp. III.
20

TRANSPIRATION IN A DESERT PERENNIAL.

 

 

 

 

 

 

155 aon
T me,
E me * ae.
ae etl tea
ee NEST .
‘i
ar erm
=> <= i =a
05; a rb Lime
’
u
Y
03 /
:
end
7”
Be oe?
Olt ea
tg
005+
Bere
gee” Sie =
a sSY eer ‘Ss
-003F Jf es ‘See
J
‘
,
,
,
oor =6T
/
7 9 u 1 3 5

Fia. 7.—Graphs for transpiration of c, March 13. Exp. III.

TasLe 4.—Transpiration of a branch in leaf (d) of an adult tree. Experiment IV.

 

 

 

 

 

 

 

 

 

 

Date. Time. z Time. E £
Mar.13.| 5517™p.m.......... Mar. 13..) 5" 15™p.m.............
Mar. 14] 6 19 am.......... } 9.00007 | Mar. 14] 6 17 am............. } 0.010 0.007
800 am. 202} 00574 78 amp 08 fate
8.25) Amis sacs \ B22 MeN it toes ate
9 29 am.......... f -00988 920) BAM sieies edicts « } 028 953
9 36 am.......... 0:82! Asin eens
10 55 am.......... } -00970 10 48 am............, } -040 ?4l
11 00 am.......... VA 04: aattics vaieeeweas
12 25 pm.......... } 00510 12 18 pm............ } -049 Abd
12 33 p.m.......... V2. B35) DiMisecina sa ceosediels
155 pm.......... } 00904 148 pmo } 052 ald
2 04 p.m.......... } 00446 3 a Li licalieve asians } 049 091
3 3 25 p.m..........0..
4 -00331 4 AD: prise sneer sernade } 022 [vee

 

 
TRANSPIRATION STUDIES.

Tasie 4—Continued.

21

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

: Dew-point. Temperature, Relative humidity.
Date. Time.
Plants, | AtMOM | aie: | Plants | AMMO | wae, | Plants | AEROM | Ate,
On KE. oC. OR; Poe, Or, p. ct. p. ct. p. ct.
Mar.13.| 5"17™ p.m. 2.0 2.0 2.0 72 72 72, 27 27 27
Mar.14.; 619 am.) —3.5 3.5 1.0 156 156 256 24 24 58
6 55 a.m. 0.5 0.5 0.5 59 59 57 38 38 38
800 am. 2.0 2.3 2.8 64 64 63 35 35 38
825 a.m. 3.0 3.0 3.0 65 65 65 36 36 36
929 am. 1.5 1.3 —0.5 72 73 71 25 24 23
936 am.) —0.5 —0.5 —0.5 73 73 73 21 21 21
1055 am.) —0.5 —0.3 —0.5 84 85 84 15 15 15
1100 am.| —0.5 —0.5 —0.5 84 84 84 15 15 15
1225 p.m.| —3.5 —3.0 1.3 86 86 86 1 ll 16
12 33. p.m. 1.5 1.5 1.5 86 86 86 16 16 16
155 pm. —3.5 —3.5 —0.1 88 89 89 10 10 13
204 p.m. 0.0 0.0 0.0 89 89 89 13 13 13
305 p.m.| —2.0 —-1.7 1.0 89 90 90 i ll 14
3 22 p.m. 1.0 1.0 T.0 90 90 90 14 14 14
423 p.m.) —2.5 —2.0 2.0 84 84 84 12 12 18
150 min. 248 min,
T
BE
L 35 eer
ee
L 80
Los.25 pee ee
04.20 gene f \
, ° es ees 2
Log .18 aye’ E
‘ et Sig a —
b.02.10/ we Be z
+ .O1-e”
Loo ~
T Pa
+009 Fi ‘ >
a ‘ Zi \
+.008 ; x pS
/ } i. ‘
+ 007 ’ 6 ‘
if iN ie \
t \
+.006 / eer \
aoe Noe \
+.005 ‘ yo, a
t 3
if *
r.004 q x
i . #
+003 i
‘
L.oo2
4
+.001
‘
+ . : i ; 5; ‘
6 7 8 9 10 ll 12 1 2 3 4 5

Fig. 8.—Graphs for transpiration of d,a branch in leaf from
an adult tree.

Exp. IV.
22 TRANSPIRATION IN A DESERT PERENNIAL.

Taste 5.—Transptration of a branch in leaf (e) of an adult tree. Experiment V.
Date, March 29, 1911.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

\ T
Time. T. Time. E. E

0.00382 0.030 0.126

-00618 037 166

00835 046 -181

00398 -050 079

- 00636 -051 124

00545 052 105

TERE HOO CeR OY Ritesh ne RENCE RRB ORR TE TED Stee Be da ld

IEEE ter nt PORES POSH OPERA NEES ORT Scat | cata

Dew-point. ‘Temperature. Relative humidity.
Time.
Atmom- : Atmom- . Atmom- .
Plant. eter: Air. | Plant. eter. Air. | Plant. eter: Air.
Oe: 2.6; OCs oR OF: oF, | pict. p. ct. p. ct.

—3.0 —3.0 —3.0 66 66 66 22 22 22
= A) —8.5 —7.0 71 72 a1 12 12 4
—7.0 —7.0 —7.0 72 72 2 4 13 4
0.5 0.2 —2.0 82 82 83 19 18 14
—2.0 —2.0 —2.0 83 83 83 14 14 4
0.0 0.5 —2.0 88 89 88 14 14 14
—2.0 —2.0 —2.0 88 838 88 11 11 u
0.0 0.3 —4.0 90 90 89 13 14 9
4.5 4.5 —4.5 89 89 89 9 9 9
—2.0 -1.6 4.5 91 91 90 1 sat 9
4.5 4.5 —4.5 90 90 90 9 9 9
—0.5 —1.6 4.5 91 91 90 12 12 9
—5.0 edad —5.0 89 89 9 9
—5.5 —4.5 89 88 9 10
4.5 4.5 88 88 10 10
—5.0 —4.0 89 sa 84 9 u

 

 

 
TRANSPIRATION STUDIES. 4 4%] 23

 

P.15

r.10

r.05

 

05 Sere
r.04
t.03 et
F.02

r OL

+008
007 mos

+006 i \ a T
L005 phe mage RT Ra

+004 es \

L 1003 ¥
L.002 pa

F-001

 

 

 

rc a 2 6 ne or Ue ee
Fia. 9.—Graphs for transpiration of e, a branch in leaf from an adult tree.

EXPERIMENT VI.

The subject of this experiment was a potted plant which had been raised
from seed in the green-house and then placed in the open for about 4 weeks
before the beginning of this experiment. At this time the plant was about
a year old. It is called No. 1 and appears in later experiments under the
same number. The area was found to be 52.95 sq. cm., but since the leaves
were not removed for measurement until April 24 a small amount of growth,
which took place in the meantime, makes the amounts per square centimeter
in this experiment slightly too small. The movement of the leaves differed
from that of the trees, in that closing did not begin until after readings had
been commenced. A record of the position of the leaves appears in this and
subsequent experiments involving potted plants, in the form of two small
lines placed below the corresponding readings on the curves. The angle of
separation of these lines represents the angle of openness of the leaves. The
relative humidity in the case of all potted plants was taken by a hygrograph
record and not by the dew-point, as in the case of the bell-jar experiments.
The atmometer used was No. 850 in the Livingston series and was found to
be equivalent to 85 sq. em. of free water surface. Plant and atmometer
24 TRANSPIRATION IN A DESERT PERENNIAL.
were placed in the open and brought into the laboratory for weighings. The
wind velocity was high all the morning, remaining so without apparent

change until 2 o’clock, when it increased to at least 25 miles an hour.

TaBLE 6.—Transpiration of potted plant No.1. Experiment VI. Date, April 12, 1911.

 

 

 

 

 

 

 

 

 

 

 

7 L Relative
Time. tT £ | E Temperature. humidity.
°F p. ct
Ch AMMA MM seus ece, Nl demmaas: | varus 72 26
9 48 a.m. | 0.00897 0.0361 0.248 78 22
10 47 a.m. -00945 0413 - 228 83.5 20
11 48 a.m. 00945 0433 .218 84.5 il
12 48 a.m. -00897 -0461 194 89 9
1 47 a.m. 00924 -0505 - 183 88.5 8
2 47 am. -00908 0508 .178 86 8
3 48 a.m. 00831 -0472 1768 80 9
25 Ez 2 be
hop oe.
# Weel, ieee ie Pi
5
-10
.05
r.00
P05 7 ee
O04 E Jee
gee
-03
-02
.O1
00
T ae TS See
r 008 se Rens camera
——
f.007
-006
r.OU5
r 004
.003
.002
001 et REN v " " u UV

 

 

 

$s 9 0 HW WL 8 4
Fic. 10.—Graph for transpiration of potted plant No. 1.
Exp. VI.
TRANSPIRATION

STUDIES. 25

Experiment VII.

Subject, plant No. 1; area, 52.95 sq. cm
to 143 sq. cm. of free water surface.

Atmometer No. 812, equivalent

Situation, in the open, exposed to sun

and wind, sun continuously bright all day. The wind movement was very
slight up to 3 p. m., when the velocity increased markedly and continued

high until the close of the experiment.

TaBLe 7.—Transpiration of potted plant No. 1.

Experiment VII. Date, April 23, 1911.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 T Temper- | Relative
Time. T | E E ature | humidity.
On Fs p. ct.
8b5Imam.| ...... | 00... | woes 3 23
10 05 a.m. | 0.0129 | 0.0300 0.430 79 a
11 18 a.m. 0192 0363 -526 86 19
12 10 p.m. 0149 0405 368 88 18
1 36 p.m. 0198 0440 7-450 89 18
2 22 p.m. 0197 0435 1452 90 17
3 23 p.m. 0198 0472 7419 88 17
4 24 p.m. 0139 .0570 1244 87 17
5 24 p.m. 0100 (0475 .210 86 17
TIE z
eo
Y
L019 n ! ;
a ‘ ’ y
L018 en ‘ '
t ‘ ‘ \
1 ‘\ - Es
017 ‘ A i \
: \ ‘ ;
4
016 | oe \
‘
Lol as .
a L
014 é : on
5 V
013 ane See i"
;
012 S
\
OL 55 * %
2 \
010 50 ==
ass 1
009 45) Es RECA esha, \
e : ty ‘
008 40 a ‘ i
. :
WUT 3) 5 1
. ’
, .30 \ !
006 an
eee i
005] .05 | .25 s = BN ‘
{ ment yet See weer
004} .04 | 20] zs ay \
1.003} .03 | -15 | ——*— \ '

: I
+.002] .02 | .10 ;
t.o01] .o1 | .05 _

Vv, A u i! ij iW Fi ut ‘ uw x. " it ii
9 0 WH w2 1 2 8 4 «5 6

Fig. 11.—Graph for transpiration of potted plant No. 1.

Exp. VII.
26 TRANSPIRATION IN A DESERT PERENNIAL.
;
Experiment VIII.
. Subject, plant No. 1; area, 52.95sq.cm. Atmometer No. 812, equivalent
to 143 sq. cm. of free water-surface. Situation, in the shade in a well-
lighted room of the laboratory.

TaBLE 8.—Transpiration of potted plant No. 1, in the shade. Experiment VIII.

 

‘ iE Temper-
Date. Time. T | E | E ature.

 

OF,
Apr. 23..) 5b 24Mp.m.] ...... 0 | ..2... | nee ee wie
Apr. 24..) 9 59 a.m.| 0.0022 et 0.241 77

 

 

 

 

 

 

 

 

T E TL
E .
.80 :
aw
75 »
70
65 F
<
t 60 !
3B =
r
50 . CE
45
t.008 = .40, i eX
; o \
L007 35 i ae \
: a > Z
t.006 30 : Z eae
: an
005 25 3 g
004.20 of
/
r.003 15 7
ao
r-002 10 E
=
}.001 —.01—, 95 —————+ ++» + + *
ie, San Od

 

a

8 9 1 lu 12 1 2 3 4

Fia. 12.—Graph for shade transpiration of potted plant No.1. Exp. VIII.

EXPERIMENT IX.

Subject, four potted plants, Nos. 1, 2, 3, and 4 (see plate 1B). Plants
Nos. 2 and 3 had the same history as No. 1, while No. 4 was the only survival
of some 30 which had been taken from their natural position in the soil and
placed in pots several weeks before. No. 4 was a seedling which had germi-
nated in the spring of 1910. It was in full leaf at the time of transplanting,
TRANSPIRATION STUDIES. 27

but lost its leaves immediately and gained a new set after two weeks. The
areas were as follows: No. 1, 68.31 sq. em.; No. 2, 75.70 sq. cm.; No. 3,
101.67 sq. cm.; No. 4, 13.11 sq.cm. No.1 had acquired a new set of leaves
since April 25, when they were taken off for measurement.

Tabie 9.—Transpiration of four potted plants. Experiment IX. Date, June 30, 1911.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

i | TT T2 Ts t% Rel.
Time. TM T2 | Ts | Ts | Eo | a, | Bo | Ew | Zw Temp. | hum.
i | °F, | p. ct.
4 17™a.m.\! 9 q9926 | 0.00125 | 0.00045 | 0.0001 | 0.0100 | 0.026 | 0.125 | 0.045 | 0.010 |{ 75 |e
8 17 a.m.| .00758 | .0074 | .00728 | .00495| .0363| .209| .204| .200| .136] 78 37
10 12 a.m.| ‘0174 0159 | [0130 | :00229| :0477| :367| 1333 | .273 | .048| 85 32
11 21 a.m.| ‘0193 0168 | [0130 | 00526] :0502| ‘384 | 1334] 1258] .105| 89 31
12 18 p.m. | 10295 0198 | :0138 | ‘00961! :0570| 1395| :347| 1242 | .168| 92 29
1 38 p.m.| ‘0212 0196 | 10152 | [00850] [0840 | :331| .306] .237| .132) 97 28
a)
# ~
+ 022 OOS
fa mi No. 1
+021 Hy
‘
+020 6 ee No. 2
muatins oh
L |
019 eo A
, /
+.018 iP 5
anc ae aE
r.017 ' —_
<: roe
L016 a
rd —»— No.3
015 if f
i] af
L014 ey +
‘7 .
L 013 t= Fg
fof
r.012 fog
it -
Ou py Se
7] it
L010 vee tals
th gf i N,
fo 4
+009 i i N No. 4
Mh aici
+008 =.
eee !
eer
t.007 it !
ty
t 006 a /
i! —
m /
005 (al :
fi i / ~\ Ba
r-004 hn j / N, /
1) y /
+ 003 ji / / Ns és
gg x
“i 7 3
+. 002 a so
s tf
—— Ss
+001 / ! /
SS ,
7 8 8 © Ut ©

Fia. 18.—Graphs for actual transpiration of four potted
plants. Exp. 1X.
28 TRANSPIRATION IN A DESERT PERENNIAL.

The atmometers used were No. 245, white, and a brown* one of the same
type, which was not numbered in the series, but is called No. 10 for conven-
ience. The white atmometer was accidentally destroyed before restand-
ardization was made and therefore the readings for it are not comparable
in actual amount to the brown cup nor to any other readings in the other
experiments. The equivalent for the brown cup was 178 sq. cm. of free

 

 

ae so
r .06 ee E
ee
r 05 —_
r 04 reise
—
03 Pe
a
02 x
4
4
1 +
5 v v " " u " uw Nod
2 v v " " n a u- No. 2
ae v Vv “" a u " No 3
v vou " " tt " u No. 4

 

 

 

 

Fia. 14.—Graphs for relative transpiration of four potted plants,
brown atmometer being used for evaporation rate. Exp. IX.

water surface. The situation was in the open with exposure tosun and wind.
A heavy wind threw sand on the pots and thus spoiled the readings after
1538"p.m. The atmometer readings for 24 47™ p.m. show that the maxi-
mum evaporation for the day was between 12 noon and 1530™p.m. Air
movement was confined to a very gentle breeze during the period covering
the readings.

 

*Livingston, B. E., A radio-atmometer for measuring light intensities. Plant World,
XIv, pp. 96-99, 1911.
TRANSPIRATION STUDIES. 29

EXPERIMENT X.
Subject, plants No. 1 and 2; areas, not obtained. Atmometers, No. 496
and brown cup No. 10. Situation, in the open, with exposure to sun and
wind. On July 27 the leaflets were closed during the entire time of the

TaBLE 10.—Transpiration of potted plants under different conditions of soil moisture.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Experiment X.
, T1 v1 T2 T2 +80 =| Temper- | Relative
Time. T1 T2 | Ewe | Eto Em Ew Eos Ew Buss ature. | humidity.
July. 27.* oF, p. ct.
Oh Sama@smis || sasien. lh Caen’ | aes [i atic: Pm kee cae anaes | aeee A | leone spied 82 57
10 12 am. | 2.51] 1.26) 3.40] 4.10 | 0.738 | 0.612 | 0.370 | 0.307 1.20 86 47
11 09 a.m. | 3.34] 2.48) 3.82] 4.62 4 . 723 649 537 121 89 44
12 11 p.m. | 3.34] 2.48] 4.64] 5.12 719 652 534 484 1.10 91 43
1 04 p.m.|} 3.90) 2.68 | 4.89) 5.21 797 748 548 514 1.06 92 45
2 16 p.m. | 3.36] 2.24] 4.30] 4.65 781 . 722 521 481 1.08 92 45
3.16 pm. | 3.22] 2.14] 4.11] 4.61 783 698 521 464 1.12 92 44
Aug. 5.f
B24! gems | eee see tae Pie eee ae eel ot nestor cam ees Ny sea $e 89 36
9 30 a.m. 09 OTE saectiase’ Marhssthact]: saves hadpsndll opeaceiarg] ouks oeeatec'l| saeeeeeee eae 93 31
10 13 am. 07 .09 | 4.90 | 6.22) .0143 | .0112 | .0183 | .0144] .... 96 32
1117 am, -05 -06 | 6.48 | 7.88] .0077) .0063 | .0093 |; .0076, .... 98 30
12 06 p.m 07 LOB) | crssssnte’ | stevazouse I iereszuneate | saeesagaseee | eas sade ll ie. sees eeu 101 22
1 18 p.m. 10 .04| 8.85 | 10.75} .0096} .0078 | .0056 | .0041/ .... 103 22
2 08 p.m. 08 BOB) csiue. |) nape | eacatsyod. || ee agietee | am aqua ll acne aries 103 22
3 09 p.m. 07 -04 | 9.50] 10.65) .0079} .0070 | .0063) .0056/ .... 106 21
5 84 pm. | .... | oc. | 7.79] 9.16 | oe | cece bee e ee | cee eee ee one es
* Soil moisture of No. 1=14.8 p. ct. t Soil moisture of No. 1=3.5 p ct.
*Soil moisture of No. 2=15.1 p. ct. {Soil moisture of No. 2=3.4 p. ct.
A
7 rns
jb SBS E
5 Pie Sec
ae —~=_ EE
No. 10," os
, ,
No. 4964#—- A
7 : Be ~“ — T
No. 1,” ij
7 rt! July 27
aN io 4
! meee AT
fa ——
No. 2;
oes
10 ll 12 1 2 3 1 al 12 1 2

Fig. 15.—Graphsffor transpiration of two potted plants, Nos, 1 and
2, under-different ‘conditions of soil moisture. Exp. X.
30 TRANSPIRATION IN A DESERT PERENNIAL.

experiment, having closed 2 hours before the first reading. In this experi-
ment, E represents the actual loss per hour from the atmometers multiplied
by their proper coefficients. Thus, only the shape of the curves may be
compared with the other experiments, and not the amplitudes. The sun
was uniformly bright until 2 30™ p. m., after which partial cloudiness began
and continued for the rest of the day.

Immediately after the 3 o’clock reading the percentage of moisture of
the soil in the pots was determined. Small glass vials were filled with
samples of the soil by forcing them into the pots, two samples being taken
from each pot, one slightly below the surface and the other about two-thirds
of the way to the bottom. The vials were quickly stoppered and weighed,
and later were dried to constant weight at about 110° C.

The two plants were then unsealed and left without water until August 5,
when the hourly transpiration rate was again determined. During the
interval no visible change in area had occurred, so that the relative transpi-
ration rates for July 27 and August 5 are comparable, although the areas
were not obtained. On August 5 the leaves on both plants were slightly
curled and remained nearly closed continuously. After the close of the
readings for August 5 the percentage of soil moisture was again determined.
Both plants were given water at 6 p. m., and by 9 p. m. all the leaves of
No. 1 had resumed their normal appearance and within three days the plant
had begun to show growth. The leaves of No. 2 did not assume their
normal appearance, but dropped off the next day; however, by August 9
new leaf-buds were visible on No. 2. Both plants continued to grow
normally after this.

Exrrerments XI to XIII.

The subject of these experiments was an adult tree situated south of the
laboratory. Three separate branches (f, area 28.72 sq. cm.; g, area 30.02 sq.
em., and h, area 31.82 sq. cm.) were used. The entire tree was in full leaf
at the beginning of the experiment, but at the close some leaflets had begun
to fall and several neighboring trees had lost most of their leaflets. As
mentioned above, the methods used in these experiments differ from those
used in the bell-jar experiments of 1911 in the following points: (1) the
evaporating surface of the atmometer was parchment paper; (2) the atmom-
eter was placed under the same bell-jar with the plants; (8) carbon dioxide
suddenly released from high pressure was used to cool the dew-point
apparatus.
 

TRANSPIRATION STUDIES.

TaBLe 11.—Transpiration of a branch in leaf (f) of an adult tree.

Date, September 14, 1912.

31

Experiment XI.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dew-point Temperature. | Relative humidity.
Time. T E z
Bell-jar.| Air. |Bell-jar.) Air. | Bell-jar. Air.
ne 4c “Cs oF, OLR, p. ct. p. ct
m™ a.m. 0 14.0 es 20 os ye
8 20 a 0.00223 | 0.0140 | 0.169 { 13.8 | 13.0 87 85 36 a7
p2rz] oer | os] om (us| ge] | 8] x |e
eB czy oo | om] om KBs] RS) BR] E |) k
BRsz} om | om] oo Ce] a8] 8] a] B | e
{Boz} om | oe] om ( 32/ at] | BiB |e
243 Bam] 0028 | oso | om (G9) $4 | ats | a | ie |
iio Bam'}) 00200 | ors | oro {$2 | $9] a | in | ot | 10
415 p.m. 1.5 1.5 101 101 10 10
6 00 Hea -00103 009 “110 { 2.0 3.0 95 93 13 15
+20 aaa,
L.15 * :
10 % gpa -E
Beene one au
r.05
+. 00
+.05 id ear
L.04 <= >
ca \
a
+.03 sere \
fF *
t-02 ee \ E
ra
L Ol Kit
L.00
r.006 7
£ x
005 / % gates).
' \ =e Ra
+ 004 el ee uw Se
f Nat S
L003 / sts
+00 = oF
t 001 ees
W WW iT uw " we u" At Vv 4!
q 8 9 10 ll 12 1 2 3 4 5 6

Fiq. 16.—Graphs for transpiration of a branch in leaf (/)

from an adult tree. Exp. XI.
32

TRANSPIRATION IN A DESERT PERENNIAL.

TaBLe 12.—Transpiration of a branch in leaf (g) of an adult tree.
Date, September 16, 1912.

Experiment XII.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dew-point. Temperature. | Relative humidity.
Time. T E B
Bell-jar.| Air. |Bell-jar.| Air. | Bell-jar. Air.
sas og, | ec. | or, | oF. | pt. | pet
Tis am] 0050 | oom ous SF] Se] we | wa | | i
=
7 30 a.m. 2.5 2.5 79 79 22 22
8 36 ee 00492 -0298 164 { 23 0.7 83 82 17 17
8 45 a.m. 0.5 0.5 83 83 17 17
9 47 om} 00789 0470 168 { 0.0 | —1.0 93 91 12 12
too am:y| 0081 | 0573 | os S| ER] Oe] | OL
12 18 pany] 00085 | 0682 | too (“8-5 | $8 | | BM | Og 7
12 26 p.m. 4.6 | -4.6 98 98 7 7
1 28 Ha -00566 -0690 082 lene —5.0 | 102 100 7 7()
135 pm. —5.0 | -5.0 | 101 101 7 7
2 40 or 00527 -0679 076 { —4.7 | —415 | 104 102° 70); -7Q)
282 emi) cous | cow | om ($$ | 8] ae | mw | zo) re
Pere) en] com oo He | Bk |
5 15 pm. =16 |sts 92 92 10 10
6 35 a -00100 - 0066 015 [ao 2.0 80 80 15 20
sa eteee 7. e
L15 Toad
10 ° en
° oo ree T
03 he
00 ak
07 Sy
ema cs
06 a SS
oe N,
05 Zz S
4 eo
04 , :
s \
8 \
7 \
a \
a, \E
OL \
00
Av
t
007 a
, ‘ TS,
006 / \ POSE
\ Sed
ae Pa * ——
005 ew x 1 Ses
a \ t =
004 Moe x
a *
003’ a+ 3
Jd eset
002 7’ “es
whe “7
001 a
v v ” 7 u u u n W aw tt i
7 B 9 wW ll Ww 1 2 3 #4 «5 6

Fic. 17.—Graphs for transpiration of a branch in leaf (g)

from an adult tree.

Exp. XII.
TRANSPIRATION STUDIES.

‘ Taste 13.—Transpiration of a branch in leaf (h) of an adult tree

Date, September 16, 1912.

33

. Experiment XIIT.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

, Dew-point. Temperature. | Relative humidity.
Time. T E Zz
Bell-jar.| Air. | Bell-jar.| Air. Bell-jar. Air.
284 | 28 °F. | °F. | pict. | pet
6 32™ a.m. . -3. —3.0 abe hes ae
7 42 am,{| 9-00521 | 0.0245 | 0212 / 9's | —9'0 80 78 15 i6
7 85 a.m.\ -2.0 | -2.0 78 78 16 15
345 am, ‘00770 w ; 3 =19 86 83 12 id
8 55 a.m.) -1.0 | -1.0 83 83 4 1
10 00 a.m.j|  °00692 0et0 109 aa ~3.0 95 93 10 9
10 10 a.m. 2 -3.0 | ~3.0 93 93 9 9
10 10 en] 00402 0578 089 { 239 Seo ae a : 4
11 25 a.m. , 4.0 | ~4.0 | 93 95 8 8
11 35 a.m.) opens 0608 oe SE ee) ae 98 7 7
12 35 p.m.) -40 | -4.0 | 98 98 7 7
T 33 Bem}, 00508 O61: top NOS See | ae kag 9 702)
1 50 p.m.) ‘ 6.5 | —6.5 | 100 100 70@)|-7Q)
2 53 pm,j| 00485 -0581 083 | oa —40 | 103 101 9 7
3 05 p.m. ~4.0 | —4.0 | 101 101 7Q)) 7
4 05 Les SEE e0asG 079 43 =3:0 98 95 7 8
413 p.m.) 3.0 | ~3.0 95 95 8 8
5 20 paam./ -00097 O10 080 ons 10 83 S4 lt 16
foe
is
L 15 es ii
L 10 4 ptt e
Rud * oe
L 05
+00
+.06 STE xe
= aes
ra Se
+.05 > Me
e 7
r. 04 of =
x
a \
r.03 we \
a = Se is
M LE
pales
Lon
L 09
& mS
}.007 gh) Tages
if 1 =
+.006 / \ fe
i a / > x
boos | Sar Ss
. ee SK
+004 se Se
ee
L008 i
\
L002 x T
4.
L.001 reer
ior W " iT) tt ty I u Vv
6 7 8 9 10 dl 12 1 2 3 4

Fic. 18.—-Graphs for transpiration of (4) a branch in leaf
Exp. XIII.

from an adult tree.
34 TRANSPIRATION IN A DESERT PERENNIAL.

OBSERVATIONS ON TRANSPIRATION EXPERIMENTS.

1. The 18 relative transpiration curves taken in the sun all show a maxi-
mum earlier in the day than the time of maximum evaporation.

2. All of therelative transpiration curves, except those from experiments
I, II, VI, and a part of TX, show an abrupt drop after the maximum,
followed by a rise which appears sometimes an hour earlier than the time
of maximum evaporation and sometimes coincident with it, but never later.

1a. An early maximum in actual transpiration corresponding to that
of the relative transpiration appears in all of the plants growing in the open,
except those in experiments I and II. In the case of potted plants this
maximum behaves somewhat irregularly. In experiment VI it is not pro-
nounced, in VII it is lower than a second maximum, in IX it fails to appear
in the case of three hot-house-grown plants and appears as a secondary
maximum in the case of the transplanted seedling.

2a. All curves of actual transpiration of plants growing in the open,
with the exception of I and II, show a drop and rise in the morning. As
in the case of the relative curves, the potted plants differ among themselves.
Experiment VI shows the drop and rise to a small extent; IX shows a
flattening of the slope in the morning followed by an increase in the angle
of slope in the three hot-house plants and a drop followed by a rise for the
transplanted seedling; X shows straight lines followed by a rise at the time
of the drop in the relative transpiration.

3. It will be seen from table 14 that leafless seedlings and leafless branches
of adult trees give the same average for maximum relative transpiration
for the day, and that this average is lower than the average maximum for
branches in leaf, and this is in turn much lower than the average maximum
for potted plants. The one seedling which was transplanted from the open
shows a maximum somewhat under the maximum average of branches in
leaf, but is higher than two of the individual maxima of which the average
is made up.

4. The differences in anatomical features shown in the sections in figure 1
indicate that the same relation exists between the water-losing power
in leaves as compared to stems and in green-house plants as compared to
those grown in the open, as is shown in the preceding paragraph.

5. Experiment X shows that a change of soil moisture in one potted plant
from 15.1 per cent to 3.5 per cent, 7. ¢., a lowering of 76.8 per cent, was accom-
panied by a lowering of 98.4 per cent of the original amount of relative
transpiration; in a second plant a change of the soil moisture from 14.5 to
3.4 per cent, t. ¢., a lowering of 76.6 per cent, was accompanied by a lowering
of 97.2 per cent of the original relative transpiration. In only one case
were valid readings of soil moisture, at a depth of 30 cm., taken at times
corresponding to transpiration readings from trees, and this shows that a
change in soil moisture from 14.0 per cent on March 27 to 32.0 per cent
on August 22, 7. e., an increase of 128 per cent, was accompanied by a
change in relative transpiration from 0.181 on March 27 to 0.302 on August
22, 7. e., an increase of 72.3 per cent.
TRANSPIRATION STUDIES. 35

DISCUSSION OF TRANSPIRATION EXPERIMENTS.

Livingston* found a similar early maximum for relative transpiration in
the case of potted plants of. four species, but:in general he did not find an
early maximum in the actual transpiration, nor does he mention the rise
succeeding the drop. It is possible that his readings were taken at too
long intervals to bring out the phenomena. In the above experiments,
Nos. I and II are mentioned as exceptions, but in these cases readings were
taken at too great intervals for the drop and rise to appear if it existed. It
may be noted that their afternoon curves for relative transpiration approxi-
mate straight lines. Although the drop and rise do not appear in plants
Nos. 1 and 2 used in experiment IX, there is a corresponding decrease in
the angle of the slopes of both the actual and the relative transpiration-
curves which is followed by an abrupt angular increase. Plant No. 3 of
this experiment shows the drop in relative transpiration, but no rise up to
the time the experiment had to be discontinued, while No. 4 shows both
drop and rise. In the case of experiment VI the closing of the leaves took
place at such a time as to interfere with conclusions regarding the drop and
rise. The closing of the leaves undoubtedly cuts down transpiration from
the dorsal surfaces, since the air in the narrow space between the leaves
would quickly rise in humidity. The second hour during which the leaves
were closed showed a slight rise in actual transpiration over the first hour,
but this made a very small change in the angle of the relative transpiration
curve and might easily be due to an increase in transpiration from the
ventral surfaces resulting from an increased vapor pressure within the leaf
which would be caused by the lessening of evaporation from the dorsal
surface. Thus it seems necessary to omit experiment VI altogether from
the discussion of the occurrence of the drop and rise mentioned. In all the
other experiments the closure of leaves took place too early in the day
to influence the drop and rise. It will be noted that in the cases of trees,
where the drop and rise is most pronounced, the leaves were closed by 5 a. m.

There is, then, in all of the above experiments, no clear negative evidence
for the existence of a drop and rise; and from the experiments the generali-
zation may be made that in trees, leafless and in leaf, a distinct drop and
subsequent rise occur in both the actual and relative transpiration, in the
morning before the time of maximum evaporation for the day; and that
potted plants show a tendency towards the same phenomena, but in some
cases the drop appears only as a straight-line “jog” in the relative trans-

_piration curve.

An inspection of the values summarized in table 14 shows the following.
The relative transpiration maxima which occur immediately preceding the
drop in the relative transpiration curves vary so much that it can not be
said that any relation exists between the amount of relative transpiration
and the occurrence of the drop. However, the values for the actual trans-
piration at this period do show a tendency towards a constant value for
the different forms used, so that it may be said that approximately 0.0044

 

*Livingston, B. E., Carn. Inst. Wash. Pub. 50, p. 63.
36 TRANSPIRATION IN A DESERT PERENNIAL.

gram per square centimeter represents the average maximum for leafless
forms, 0.0079 gram for adult trees in leaf, and 0.0164 gram for green-house-
raised plants. Experiment VI was omitted from the series because of the
error in area which has already been mentioned; so also was VIII, because
it represents readings in the shade and does not show the drop.

TaBLE 14.—Summary of some of the data from Experiments I to XIII.

 

Maximum preced- | Minimum during | Maximum succeed-

 

 

    

 

 

 

 

 

 

4 T cere Uy acehuin
ing drop in = rop in = ing drop in or day.
Subject. E £ zE
T T T T
Ez T E z T E z T E E T
Leafless seedling:
Ex. I. 10.0040 (0.019 |0.061 (0.0056 (0.052 0.072 |0.0028 (0.040 10.213 [0.0056
Ex. II.. 0045 | .033 |... 136 | .0052
Ex. II.. 0041 | .034 -120 | .0048
Average...... 0... cece eee A563} 20042 itis yeoalee sanaliaasinuclags de oleic’ ha abeegralcva eel selene .156 | .0051
Leafless branch of tree:
i TS cectatnapins ecanigndicvtae Sis 151 | .0057 | .038 | .068 | .0034 | .049 | .075 | .0038 | .050 | .151 | .0060
Px: DED sacha en at cetncun aeons 158 | .0035 | .038 | .C69 | .0081 | .044 | .078 | .0038 | .049 | .158 | .0043
Average... 6... eee eee eee .155 | .0046 |...... -069 | .0033 |...... -077 | .0038 |...... 155 | .0052
Branch of tree in leaf:
FAX. TVs seesiag ote Soesneerdis te oan 353 | .0098 | .028 | .104 | .0051 | .049 | .174 | .0090 | .052 | .353 | .0098
Ex. Wis tice ets cries .| .181 | .0083 | .046 | .079 | .0040 | .050 | .124 | .0064 | .051 | .181 | .0083
WER OD giao se istsiaye ws ..{ .205 | .0061 | .029 | .081 | .0084 | .042 | .109 | .0050 | .055 | .205 | .0061
TK OE sess: ais Scssaichisias fia Saison s .168 | .0079 | .047 | .055 | .0031 |; .057 | .100 | .0065 | .065 | .168 | .0079
Wx, DODTE  nsannab oe ei gaeutes .231 | .0077 | .033 | .069 | .0040 | .058 | .102 | .0062 | .061 | .231 | .0077
Average............0.000- .227 | .0079 |...... .078 | .0036 |...... .122 | .0066 |...... 227 | 0079

 

 

Potted plant ae 1, green-house-
raed, BE om Saath Gy i 526 | .0192 | .036 | .868 | .0149 | .040 | .452 | .0198 | .044 | .526 | .0198

Potted inhi No i
426 | .0174 | .047 | .445 | .0193 | .050 | .459 | .0225 | .049 | .459 | .0225

   
  

raised, Ex. IX.
Potted plant No. 2

 

 

 

raised, Ex. IX................ .387 | .0159 | .041 | .387 | .0168 | .050 | .404 | .0198 | .049 | .404 | .0198
Potted lant ue 3, green-house-
icine satan aeonneseiecess caceeail .317 | .0130 | .041 | none | .0130 | .050 | none | .0152 | .049 | .3817 | 0152
AVOTABC gcse cacg sins 82 geeky 414 | .0164 |......).0.0.. OLGO) | assesses tab cellent -428 | .0192
Potted plant No. 4, transplanted
from open, Ex. IX............ -158 | .0049 | .031 | .056 | .0023 | .047 | .195 | .0096 | .049 | .195 | .0096

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The maxima for experiment IX have been reduced to white-atmometer maxima by multiplying them by
1.162, a correction factor which was found by averaging the results obtained by dividing the brown-atmometer
readings by the corresponding white-atmometer readings on July 27 and on August 5. (See experiment X.)

Considering only those experiments on plants growing under natural con-
ditions which show a definite drop and rise in both the actual and relative
transpiration, it appears that the maximum of actual transpiration reached
after the dropis in five cases lower than the one before the drop, and in two
cases the later maximum is about the same as the early one, while in no case
is the second one higher than the first. It therefore appears that, for a
certain form under similar conditions, there is a maximum water-loss beyond
which the plant does not go and that this is frequently reached without a
previous decrease in the relative rate. In the case of green-house-raised
plants, where, as has been pointed out, the drop is replaced by a lessening of
the increase of relative rate and is followed by an abrupt increase in relative
rate, it appears that while there is a tendency toward a constant value for
the actual transpiration immediately preceding diminution in the increase of
the relative rate, yet it is not so marked as in the case of plants in situ. In
TRANSPIRATION STUDIES. 37

three out of four cases the later maximum is higher than the first. In these
cases, though, the relative transpiration rate again decreases before the time
of maximum transpiration rate. In all of the four cases mentioned the soil
moisture in the pots was probably higher than that in the ground, and since
experiment X throws some light on the behavior of maxima in both relative
and actual rates under different conditions of soil moisture, it is not possible
from the potted plants to draw conclusions strictly comparable with those
drawn from the plants in situ.

It seemed probable that this drop and rise have some definite internal
cause, and with the idea of obtaining some light on the cause, measurements
were taken of the following factors: (1) stomatal openings; (2) water con-
tent of leaves, stems, and twigs; (3) temperature of leaves.
38 TRANSPIRATION IN A DESERT PERENNIAL.

STUDIES INVOLVING FACTORS CORRELATED WITH TRANS-
PIRATION BEHAVIOR.

DAILY COURSE OF STOMATAL MOVEMENT.
METHODS.

For the investigation of stomatal behavior in Parkinsonia the absolute
alcohol method used by Lloyd* was tried and found to be satisfactory in the
case of leaves of potted plants and of very young plants growing in the open;
but it could not be used on the leaves or twigs of adult trees, since in the case
of the leaves much of the mesophyll adhered to the peeled epidermis and
in the case of the twigs the epidermis came off without the guard cells,
which are sunken in deep pits. An effort was made to find some method by
which the leaf as a whole could be used. Picric acid was dried at about 40°
C., cooled, and put into cedar oil until a saturated solution with picric acid
in suspension was made. Whole leaves and parts of leaves were put into
this mixture and left there until they were cleared sufficiently to be seen by
reflected electric light through a microscope. Picric acid was used because
of its known properties as a “fixative.” Since an aqueous solution could
not be used without causing a disturbance of the water content of the cells,
cedar oil was selected as a solvent, on account of its ability to penetrate and
“clear” fresh plant tissues. The theory of the action of this mixture on the
tissues is pure conjecture, but since it was the theory that suggested the use
of the materials it is given here for what it may be worth. The picric acid
is carried by the cedar oil into the tissues of the leaf, and as soon as it meets
the water in the cell walls it goes into aqueous solution and then acts upon
the protoplasmic lining within, making it impermeable to water and thus
leaving the form of the guard cells undisturbed. —

The only test for this method is of course the checking of results secured
with those obtained by some other method. Since the leaves of potted
Parkinsonia plants lend themselves to Lloyd’s absolute alcohol method,
they were used to test the efficiency of the picric acid method, readings being
taken by the two methods simultaneously. An extra check was attempted
by the use of the direct light method used also by Lloyd (not yet published),
but the leaves did not lend themselves to this method.

EXPERIMENT FOR TESTING THE Picric Acip Mrruop.

Two species of Tradescantia, Cissus laciniata, and a hot-house-grown
Parkinsonia microphylla were used for the test. Lloyd’s absolute alcohol
method worked satisfactorily on all of the plants, but neither the light
method nor the picric acid method could be used on either T'radescantia.
The picric acid method worked satisfactorily on both the Cissus and the
Parkinsonia. The numbers given in the tables represent averages of 20
readings each, which were obtained as follows: The entire preparation was
examined, the probable average size estimated, and 18 individuals near this
size were measured; then one near each extreme was measured and included.

 

*Lloyd, I., Physiology of stomata, Carn. Inst. Wash. Pub. 82.
STOMATAL MOVEMENT. 39

In most instances the majority of the stomata were about the average size.
A test of the method of selection was made by taking a leaf at random and
measuring all the stomata included in it. The average was found to be
practically the same as the one obtained by the first method. Intheopinion
of the observer the widths given represent very little error, but. where the
openings were small the lengths could not always be determined accurately.
Every measurement was made to include equal numbers of stomata on the
two sides of the leaves. The necessity for the inclusion of the stomata of
both sides of the leaves in measurements of this kind has been pointed out
by Livingston and Estabrook.*

Table 15 contains the results reduced to microns, including the length (1)
of the openings between the guard cells, the width (w) of the opening, and
the square root of their products (Wlw).t

A comparison of the curves shows that the method under discussion gives
approximately the same results as Lloyd’s absolute alcohol method. In
one respect this method seems to have an advantage over the absolute
alcohol method, namely, that the guard cells are not subjected to the danger
of loss of water from evaporation during the interval of transfer from the
leaf to the alcohol, a factor which might be serious in the dry atmosphere of
Arizona.

TaBLE 15.—A comparison of stomatal measurements taken by the absolute alcohol method
and the picric acid method. Cissus and Parkinsonia, November 17, 1912.

 

 

 

   

  
 
  
  

 

 

 

 

 

 

 

 

 

 

 

 

Absolute alcohol. Picric acid in cedar oil. Light.
l w Viw l w Viw l w Viw
Cissus.
Bh00F SI ccs od cahaed ne 71 1.4 3.1 9.1 1.4 3.5
os stan Dell 3.9 5.9 9.9 3.3 5.8
9.9 3.2 5.6 9.9 2.4 5.0
8.3 2.3 4.3 9.5 1.7 4.0
Ei -| 7.6 1.1 2.9 10.6 1.1 3.2
9.200 - PANG ities ascaaces ae 5 7.6 9 2.6 9.1 1.4 3.5
Parkinsonia.
BY OOM BM seca isce se srtersicreyecens sia 9.1 1.5 3.7 9.1 1.5 3.7 10.6 2.3 4.9
YO: 330) FUTON spats, btcxescioyscesnsivs. 84s 9.1 2.7 4.9 9.1 2.8 5.0 10.6 3.0 5.6
12 30 am | 7.6 1. 2.9 7.6 8 2.5 ove a Las
2 90: BM aewietsests aceacencas 7.6 8 2.4 6.1 9 1.5
5) 90: AeMec ond se agancees -| 8.3 2.0 4.0 9.1 2.4 4.6
After 5 hoursin dark room....| 7.6 7 2.6 8.3 1.5 3.5
After 24 hours in dark room...| Shut. 0 Shut. | Shut. 0 Shut.
EXPERIMENTATION.

EXPERIMENT XIV.

During the progress of experiment V (see page 22) leaf samples for sto-
matal measurements were taken as near the middle of each transpiration
period as the manipulation of the experiment would permit and treated with
picric acid in cedar oil, as described above. The values of 7'/E are repeated
from page 23 and are plotted in fig. 20 with the values for the square roots
of the products of the stomatal diameters.

 

*Livingston, B. E., and Estabrook, A. H., Observations on the degree of stomatal
movement in certain plants, Bull. Torr. Club, xxxrx, 15-22, 1912.

{Browne and Escomb, Static diffusion of gases, Phil. Trans. Roy. Soc. Lond., B,
vol. 192, pp. 270-292, 1900.
40 TRANSPIRATION IN A DESERT PERENNIAL.

 

   
 

 

 

 

Parkinsonia
“a y

eee 7 Picrie
+ 4.0 Alcohol

VIxw
+ 3.2
| 2.4 _» Picrie

“_ Aicohol
E16 w
+ .8
Cissus
+ 5.6
4.8
F 4.0
3.2
+ 2.4
+ 1.6
+ .8
L z 1 £ 1 L 1: seit r

 

4
8 9 10 ll 12 1 Z 3 4 5 6 7 8 9

Fic. 19.—Comparison of picric-acid method for stomatal measurement with the absolute
alcohol method.

 

 

st, EX: XVI

t2.4

r 1.6

 

 

 

 

 

.203.2 Ex. XIV

 

 

 

L a 1 i 1 1 1 1 1 1 1 1
eae 7 8 9 10 dW 12 #1 2 3 4

Tia. 20.—Graphs for stomatal openings and relative trans-
piration. Exps. XIV, XVI, XVII.

 
STOMATAL MOVEMENT. 41

TaBLe 16.—Relative transpiration and stomatal openings. Experiment XIV.
Date, March 29, 1911.

 

 

Time. | I w | Viw zt |
‘ shade 8.8 14 3.5
40 a.m. eon. 8.8 116 a7 if Oat
1 05 am... ....ccce. 4.4 6 1.6 079
VQ: LO: peta sats #2 whose 6.0 8 2.2 124
3 00 p.m............ 8.8 1.5 BRO oh pecker

 

 

 

 

EXPERIMENT XV.

Leaves and tangential surface sections of young twigs from tree A were
taken simultaneously with leaves from plant No. 1, subjected to the picric
acid treatment, and stomatal measurements were made. As a control,
stomatal measurements were also made on No. 1 by Lloyd’s method,
through the 1 o’clock reading. The potted plant was placed in the open,
about 50 feet distant from the tree. It will be seen that the agreement of
the alcohol method with the picric acid method here is not as good as in the
test experiments; however, the lack of agreement is one of actual size only,
for the two curves have practically the same shape. The guard cells of the
stomata of the tree were always smaller than those of the potted plant. The
stomata of the twigs very evidently are not movable to any extent. A few
days after this experiment measurements of the stomata of twigs were tried
and no evidence of any motion of the stomata was gained fromsome 20trials.

Tasie 17.—Stomatal measurements from leaves and twigs of an adult tree and from leaves
of a potted plant. Experiment XV. Date, August 11, 1911.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

No. 1 leaves. he
A leaves, picric acid. | .1 twigs, picric acid.
Time. Picric acid. : Absolute aleohol.

1 w Viw l w Viw l w Vilw l w Viw
4b 30™ a.m. 4.2] 0.6 1.4 4,2 0.6 1.6 5.6 1.0 Be le areas tc ose
6 00 am.j 11.6] 4.6 7.2 8.8 sah 6.0 6.4 1.3 Pa aa [eee 0 0
9 00 am 10.8] 3.8 6.4 8.8 2.5 4.7 6.4 3.4 4.7 |14.8(2)| 1.4(2) 0
11 00 a.m. 8.8) 2.4 4.5 8.8 1.5 3.6 7.6 1.1 2.9 (?) (2 (?)
100 pm. | 12.0} 2.1 5.0 7.6 1.6 3.4 7.6 9 2.7 (2) 2 (?)
2 00 pm. | 10.8] 3.5 6.1 a a ee 6.4 1.5 3.1 |14.8(4)) 1.4(4) 8
4 00 p.m.} 10.8) 4.4 6.9 soe 7.2 2.5 4.2 2 (?) (2)
10 00 p.m. 6.4] 1.0 2.7 er | 6.4 6 1.9 |312.0 3.8

1All the rest shut. 2All shut. 3A verage of 6; all the rest: shut.

 

 

 

 

5 7 9 m1 2 4 0
Fic. 21.—Stomatal measurements from leaves of potted plant and from adult tree by
the picric-acid method, with absolute-alecohol method check on potted plant. Exp. XV.

1 4

 
42 TRANSPIRATION IN A DESERT PERENNIAL.

ExrrrIMent XVI.

The subject of this experiment was an adult tree, called B, growing about
20 feet from tree A. Transpiration rate was determined by the calcium
chloride method described on page 10, and the evaporation was determined
by the use of atmometer of type 2 (C, fig. 2) under a separate bell-jar. The
area of the branch used was not determined, so that the T here represents
actual losses and not losses per unit area. Figure 20 gives the values for
Vlw plotted with the values for 7/E.

TaBLe 18.—Relative transpiration and stomatal openings from an adult tree.
Experiment XVI. Date, August 23, 1911.

 

 

 

 

 

Time | l | w | vio E z

780M 9M ones 8.3 a | 28 | vse | ose.
snade i - -

8 30 a.m. ion ee 8.0 23 | 43 } 0.032 0.235
Wo am... | 8.0 24; 4.4 | .040| 302
12 30 pm..........., ; 8.0 8 | 2'5 050 | {205
140 pm... | 8.0 12 | 311 052 | 1215
400 pam! | 8.0 14 | 3:3 | loa] 108

 

 

 

Experiment XVII.

Method, Lloyd’s for measurement of stomata.

Subjects, plants Nos. 1 and 2,and atmometer No. 10, brown. Situation,
in the open, exposed to sun and wind. Conditions, soil-moisture conditions
were made to correspond as nearly as possible to those of July 27 and August
5. No. 1 had been without water 5 days, while No. 2 had received the usual
amount. The leaves of No. 1 had the same curled appearance as on August
5, while No. 2 appeared in all respects normal, as on July 27. At the close
of the experiment, No. 1 responded to water as on August 5. The percent-
age of soil moisture was determined as before and appears in the tables. In
this experiment only the widths of the openings of the stomata are given,
since the curve of widths has been found to correspond in shape to the curve
of Viw. All measurements were taken in the bright sunlight unless other-
wise stated. At 6" 30™ a.m. and 125 30™ p.m. measurements were also
made in the shade and appear on the curvesas isolated dots abovethe corre-
sponding hours. To the left of the curve appear again, reduced one-half,
the relative transpiration rates for plants Nos. 1 and 2 under similar con-
ditions of soil moisture. So far as can be told from the evaporation readings
for the 3 days, the evaporation conditions were similar.

TaBLe 19.—Comparison of stomatal openings of potted plants under different
conditions of soil moisture. Experiment XVII. Date, August 20, 1911.

 

 

 

 

 

 

Time. No. 1, w.* |No. 2, w.f | E No. 10. |
shade 1.4 oe ‘
Gh 30" a.m. oe aera 7 8 i
9 00 a.m.,sun....... 4 2.8 5.23
10 00 a.m.,sun....... 0 1.2 6.37
11 00 a.m., sun....... 4 1.0 7.09
12 30 p.m. ae Hf ag } 8.21
12 00 pm.......eee 4 1.0 | 9.05 |

 

* Soil-moisture of No. 1=3.6 p. ct.
tSoil-moisture of No. 2=14.2 p. ct.
1Cloudiness prevented further readings.
STOMATAL MOVEMENT. 43

DISCUSSION OF STOMATAL BEHAVIOR.

In all of the seven experiments given above, the stomata of Parkinsonia
microphylla closed down and subsequently opened during daylight. Three }
of the closures took place on adult trees and four on potted plants. In all/
cases the closure began before the time of maximum evaporation for the day
had been reached. In the two cases (experiments XIV and XVI) where
transpiration and stomatal measurements were taken simultaneously from ,
different parts of the same tree, the curves of transpiration run parallel with »
the curves of the linear dimensions of the stomatal openings during the fore- .
noon, but in the afternoon depart and run in opposite directions. These
two experiments present some evidence that there is a connection between
stomatal opening and transpiration rate and that the connection is not
operative in the afternoon. The curves follow each other so closely during
the morning hours that it seems impossible to neglect their evidence, even
though the afternoon readings show evidence of the opposite sort. The
fact that the time of minimum transpiration corresponds with the time of |
minimum stomatal opening in both experiments, and that this time is not the’
same in the two experiments can not be ignored. It is well to note here that
between the dates of the two experiments the summer rains had come and
the soil moisture at a depth of 30 cm. had been raised from 14 to 32.1
per cent, and consequently the deeper layers of soil must have had their
moisture content raised proportionally. The trees had lost their leaves and
gained new ones between the two experiments. While there is no con-
vineing evidence of the direction of the cause and effect, a point might be
made against the theory that the closure of stomata is due to light effect
alone, for the difference in time of closure in the two experiments could
hardly have been brought about by the difference of position of the sun,
since the sun was about at the same distance from the summer solstice at
the two times.

A reference to pages 19-29 shows that while the time of the morning mini-
mum relative transpiration is fairly constant for a given tree on successive
days, it is by no means constant in the case of potted plants. Thestomatal
openings may be compared with the relative transpiration when the readings
are taken simultaneously from the same tree, but a reference to experiment
IX will show the impossibility of making such hourly comparisons in the
case of two potted plants unless the plants used can be shown to have parallel
hourly curves of transpiration. Several attempts were made to get stoma-
tal readings from one potted plant and transpiration from another which
had been found to give a similar relative transpiration curve, but various
interruptions of weather and accidents to the plants prevented good
readings. The curves given above show that there is some connection
between the relative transpiration and the size of the stomatal opening, but
there is no evidence of the relation of cause and effect nor even of priority
of time.
44 TRANSPIRATION IN A DESERT PERENNIAL.

Experiment X, which was an attempt to investigate this relation in
another way, brings out the fact that the relative transpiration of a plant of
potted Parkinsonia microphylla in a soil of 3 per cent moisture is only one-
sixtieth to one-hundredth the amount the same plant gives when its soil
moisture is 14 per cent, and that this change takes place without loss of
leaves. Now, experiment XVII shows that when the same plants, which
experiment X shows behave similarly under similar conditions of soil-
moisture, are run together under identical atmospheric conditions but under
different conditions of soil-moisture, the stomatal diameters in the plant
having a soil of 3 per cent moisture are about one-seventh of those from the
plant having a soil of 14 per cent moisture. Evidently a lowering of the
soil moisture means a lessening of the relative transpiration and also a
shutting up of the stomata, but it will be noted that the-transpiration rates
are not proportional to the linear dimensions of the stomatal openings.

Lloyd’s calculations for Fouquteria splendens* show that the closure of
stomata is not the cause of changes in relative transpiration rate. This is
perhaps true of other plants, and with this in view the following hypothesis
was framed as the starting-point for the work which follows. The morning
drop is caused by a deficiency in water in the transpiring tissues, due in turn
to the supply from the lower tissues not being equal to the demand of the
evaporating power of the air. This deficiency of water in the leaves causes
a closure of stomata simply because water is drawn from the guard cells in
the same manner as from the other cells. The diminished size of the open-
ings would cause a rise of humidity within the intercellular spaces and thus a
checking of the evaporation rate within the leaf, even though the stomata
did not close down enough to check the theoretical amount of vapor diffused
through the openings. Thus the closure may act to further check transpi-
ration, and meantime the ratio of outgo to intake has lessened and all the
cells, including the guard cells, gain water and the latter open mechanically,
after which transpiration goes on more rapidly, but does not reach the former
high rate unless the ratio of outgo to intake reaches unity. However, in the
case of young plants without leaves the early maximum and drop occur;
and in the case of the leafless branch of an adult tree the drop is followed by
a subsequent rise. It will be seen from table 17 that the stomata of twigs
remain nearly closed all of the time, and this leads to the conclusion that the
lessening of the relative transpiration rate before the maximum evaporation
rate for the day has been reached may take place without a change in sto-
matal opening.

In experiment I the readings were not taken at frequent enough intervals
to discover a rise after the drop, if it occurred. In experiment II a flattening
of the curve occurs after the drop, but no distinct rise; while in experiment
IV the rise after the drop is less in amount than in cases where plants in
leaf were used; this may mean that the closure and subsequent reopening of

 

*Lloyd, F. E., The physiology of stomata, Carn. Inst. Wash. Pub. 82, pp. 136-137, 1908.
WATER CONTENT OF PLANT PARTS. 45

the stomata aided in the rise but are not necessary to it. So, then, a defi-
ciency of water in the evaporating tissues would be the first cause of the drop
in transpiration rate, while the evaporation rate is still increasing. If now
the supply of water from below is unchanged, the smaller evaporation rate
would allow a balance to be obtained when we should expect the relative
rate to become a straight line for a time at least. It is hard to see how the
gain could be sufficient to send the relative rate up again unless some other
factor entered, either to check the rate of outgo or to increase the rate of
intake from the lower parts. If Dixon’s hypothesis* of the ascent of sap be
accepted, it might be supposed that the deficiency of water in the terminal
tissues causes a “pull” on the water columns, which enter the tensile state,
and thus the intake is increased. As soon as the supply begins to catch up
with the demand the tensile pull is lessened and the relative rate begins to
go down again.

If the explanation is the latter one, based on Dixon’s hypothesis, then
there might be a relation between the moisture content of different parts of
the tree which would throw light on the matter. Consequently a series of
moisture content determinations was carried out as, follows.

DAILY COURSE OF WATER CONTENT OF LEAVES, TWIGS, AND STEMS.
EXPERIMENTATION.

ExpermMEeNT XVIII.

Three adult trees, designated I, II, III, were selected in open sunny
places, and at two-hour intervals small limbs were sawed off and samples for
the determination of water-content were taken as follows: Ij, IJ,, and III;
were end twigs about 3 to 5 cm. long, with diameters from 0.1 to 0.2 cm.;
I,, Iz, and ITI; were taken about a meter from the end twigs and had diam-
eters about 1.2 to 1.6 cm.; Is, Iz, IIs, were taken 2 meters from the endtwig
and were from 3.5 to 3.9 cm. in diameter. The work of sawing and cutting
was done very quickly, with the aid of an assistant, and the pieces were
weighed immediately after the cuts were made. The samples were allowed
to dry in the sun for about a week and then dried to constant weight in an
oven at 95° to 100° C. Accidents which happened to the end twigs of II
left too few good readings for the results to be plotted. For the sake of a
comparison with the water-content of a tree which had lost no branches,
samples were taken from a fourth tree at 2" 30" p.m. The two readings
marked III, and IV, were taken about 4 meters from the tips, where the bark
is brown and not green as in the other samples. In the sawing great care
was taken to get branches widely separated on the tree, in order that the
wounds might cause as little disturbance as possible. The evaporation rate
was measured by exposing atmometer No. 11-1 in an open sunny place.

 

*Dixon and Joly, On the ascent of sap, Proc. Roy. Soc. Lond., vol. 57 B.
46 TRANSPIRATION IN A DESERT PERENNIAL.

TasLe 20.—Water content of stems and branches of adult trees. Experiment XVIII.
Date, August 5, 1911.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time. I | Te TI3 |} Ih Ie | IDs | UN, | Io | ITs | IY, | IVi | TV2 | TVs} [Vs | Eu-i
| : ae a
t
4) 30m a.m. | 87 68 58 |... | 73 62 97 63 64 50
8 30 a.m. | 85 66 68 87 | 68 61 93 60 61 a
10 30 am.| 77 | 58 |. 61 |... ] 67 67 97 63 61 oe war Psd cess TOF
12 30 p.m. | 73 63 66 |... |] 70 70 78 72 60 i «. fee | .. | 046
2 30 p.m. | 77 64 63 93] .. 70 93 59 62 97 81 | 61] 60 | .061
5 00 p.m. | 85 66 62 |... | 7 73 of 61 63 dy ee ea 055
9 30 pm.| .. 66 |. 59 | 100) 68 | 64 90 62 60 .

 

 

Ex. III

 

 

 

 

 

Fic. 22.—Graphs of water content measurements taken simultaneously from two adult
trees at three different distances from the ends. Graph for relative transpiration of a
leafless branch repeated at top of figure. Exp. XVIII. ,

EXPERIMENT XIX.

Subject, the tree from which branches f, g, and h were taken. (See experi-
ments XI to XIII.) End twigs about 3 to 5 cm. long were cut off, the
” leaves quickly severed, and the leaves and twigs placed in separate air-tight
shallow weighing-bottles. The bottles with their contents were weighed on
good chemical balances to 0.001 gm., and the contents were then transferred
to glass beakers and protected from dust, etc., by filter-paper covers. The
beakers and their contents were then dried to constant weight in an electric
oven at 72° to 75° C. By the use of the above precautions it was possible
to obtain the water-content, of the small amount of material which it was
necessary to use, accurately to 0.2 per cent. Calculations were made as
before for percentage of dry weight of the material used. At noon and at
2 p.m. samples were taken from another tree about 30 yards distant: In
table 21 these appear under the heading “Series II.”
WATER CONTENT OF PLANT PARTS. AT

Since the manner of shading used in the transpiration method described
above requires attention at least as often as every 10 minutes, it was not
practicable to obtain both transpiration and water content readings on the
same day, and in order to obtain the two sets of readings in comparable
form the water content experiment was preceded and followed by transpi-
ration readings, transpiration of branch f (see p. 31) being taken on Sep-
tember 14, water content on September 15, and transpiration of branch g
on September 16. No samples were taken from the limb from which came
the branches used for transpiration.

In order to obtain an approximation of the water content at the time
corresponding to the transpiration readings, which it will be remembered
were plotted to the middle of the time period, lines were dropped from the
transpiration readings until they intersected the curves of water content

Taste 21.—Water content of leaves and their twigs. Experiment XIX.

 

 

 

 

 

 

 

 

 

 

 

 

 

Series I. Series II.
Date. Time.
Leaves. | Twigs. | Leaves. | Twigs.
1912. p.ct. p. ct. p.ct. p. ct.
Sept. 14...) 900" p.m. 109.1 O50 1 sees sny mand
Sept. 15...) 7 40 a.m. 102.4 TEA sees ei
8 45 a.m. 97.3 (Bint | -secease ale
9 45 a.m. 98.2 SE Me in tases Loe
10 45 a.m. 98.2 T3.0 | aden ts
12 00 m. 101.1 74.4 103.0 74.4
2 00 p.m. 102.7 78.2 102.0 72.2
4 00 p.m. 105.1 806) seas eye
5 30 p.m. 103.3 G:F eaten
Sept. 16...| 4 30 am. 109.4 HBee “| eae
r.20 qe %
15,
, ae He 2 T
10 Legere se: af B
aan Sete caecc Pode p E
05. l ice
+00 ee is See
Leaves : a
100 PN a shige
PS NES AMS apetep ee = en tae
+95 ae 22
+90 Water content
r 85 |
‘ a a
19) Se uproot S Ne | com ed
Twigs bee on ate a
r70 mere) Ty ee
65

 

 

 

 

 

 

 

 

 

 

 

 

1. a 1 i 4 1 1 1 1 i. L 1 >a
Tt « os 8 i a © 1 2 6 4 3
Fig. 23.—Graph for moisture content of twigs and their leaves for September 15, 1912,
plotted with relative transpiration for September 14 and 16, Exp. XIX.
48 TRANSPIRATION IN A DESERT PERENNIAL.

and a new curve was made by connecting the points of intersection. Figure
23 gives these resulting curves one space below their actual position in order
to avoid numerous intersections with the original curves. This method of
obtaining curves comparable in time is based on the assumption that both
the relative transpiration and the water content change at a constant rate
between the successive readings.

DISCUSSION.

The curves resulting from the plotting of water content determinations
of the two trees, I and II, are fairly consistent in general shape. In the
case of the end twigs there is a minimum water content about noon followed
by a subsequent rise. The decrease begins in one case about 8" 30™ a. m.
and in the other at 10" 30™ a. m.; in the former case recovery is slower than
in the latter. In the case of branches a meter from the ends it may be said
that in general the slopes of the curves are in opposite directions to the
slopes of the twig curves. The branches 2 meters from the ends behave
differently in the two trees; in Isthe curves are, in general, parallel to the I,
curve, while curve III; is nearly flat or only slightly lower in the middle of
the day than at the two ends of the day.

The curve of relative transpiration from experiment III (see p. 20) is
plotted at the top of fig. 22. Although-experiment III was performed in
March and experiment XVIII in August, the conditions of soil moisture and
evaporating power of the air at the two dates make it seem fair to compare
the two sets of readings. The soil moisture at a depth of 30 cm., as given by
weekly determinations made by Dr. Forrest Shreve, was 15 per cent on
March 12 and 15.7 per cent on August 6. The summer rains which had
intervened allowed for recovery from the extreme conditions of drought
obtaining during the arid fore-summer. It may be, of course, that trans-
piration conditions were different in the two cases, but the probability is that
they were much the same.

The following theory for the behavior shown is suggested. The relative
‘transpiration rate increases until about 9» 30™ a. m., when the demand for
' water made upon the plant by the evaporating power of the air exceeds the
supply of water furnished by the transfer from the lower portions of the plant,
and there results a slight drying out of the walls of the cells which form the
true transpiring surface, both internal and external. This operates in two
directions: the one, a lessening of the relative transpiration rate because the
evaporating surface of the intercellular spaces has receded into the pores of
the cell walls; the second, an assumption of the tensile state of the water in
the vessels and cell walls, which results in a “pull” of water from the lower
portions of the same stem and, as an immediate result of this, a transfer
of water from lower to higher portions faster than the supply still farther
down can stand, and therefore an increase in the size of the air bubbles in
the vessels caused by the vacuum formed and hence a lower water content
WATER CONTENT OF PLANT PARTS. 49

of the branches 1 meter down. Then 2 meters down the stem the effects
might either lag behind those above or, being influenced by the same extra
pull, might draw enough water from the portions still lower to keep up with
the water content of the higher portions. Indeed, it would be impossible
to predict the condition of any portion below the end or those very near the
end. To return to the relative transpiration curve at 10° 30™ a.m., it will
be seen that the rate is now lessened as a result of the drying out of the
tissues. This decreased transpiration gives the water supply a chance to
catch up with the demand and a straight line of relative transpiration might
be expected for a short time at least; but here a marked increase in the
water content of the twigs is observed, accompanied by a decrease 1 meter
below. This increase is accompanied also by an increase in the relative
transpiration above, a natural result of the water films coming nearer the
surfaces of the pores.

Experiment XIX differs from experiment XVIII in that the tree was in
leaf and that the transpiration rates are more surely comparable with the
water content readings. An inspection of the curves shows the following
facts. The relative transpiration increases until about 9" 30™ a. m., being
accompanied by a decrease in the water content of the leaves and anincrease
in that of the twigs. Until 11° 30™ a. m. the water content curves of leaves
and twigs slant in opposite directions, after which time they run parallel.

Bearing in mind the theory mentioned in the preceding paragraph, the
following points are evident: The increase in relative transpiration up to
9 30" a. m. brings demand greater than supply, causing a decrease in the
water content of the leaves; this in turn throws the water in the tissues into
a tensile state, causing a rise of water content in the twigs by the water
.| brought up from below. From 930" a. m. to 10530™ a. m. the transpiration
‘rate is decreased, caused by the lowered amount of water present, but at

the same time the water content of the leaves is slightly increased by a
“pull” which lowers the water content of the twigs. By 105 30™ a. m. the
transpiration and relative transpiration have been able to increase because
of the rising water content of the leaves, but this water is gained at the
expense of the twigs and it is not until after 12 noon that the lower portions
can supply water fast enough for the water content of twigs and leaves to
increase together. During the afternoon the relative rate fluctuates slightly
from a straight line. From 4 p.m. to 5 p.m. the two transpiration curves
go in opposite directions, so no conclusions from their comparison with the
water content can be made.

In cases of this kind, where the tree is in leaf, the drying out is probably
accompanied by a closure and subsequent opening of the stomata, as was
mentioned in the section on stomatal behavior. The fall and rise in relative
transpiration may occur more frequently than the readings at hourly inter-
vals show. In fact, it is possible that here is an explanation for the well-
known small fluctuations in relative transpiration observed when readings
are taken at very short intervals. On page 6 is a brief description of the
50 TRANSPIRATION IN A DESERT PERENNIAL.

dying of twigs, branches, and finally limbs, which takes place during
times of drought. This would happen when the tensile “pull,” due to a
deficit of water in the upper tissues, became great enough to cause a break-
age of all or nearly all of the water columns. The twig would then quickly
die for want of water, even though the lower portions remained alive.

On page 36 mention was made of the fact that there seems to be a relation
between the amount of the maximum of actual transpiration immediately
preceding the drop and the occurrence of the drop. This fact seems to
accord with the theory given above, the maximum amount of actual trans-
piration for any tissue being a fairly constant factor dependent for each
tissue upon its structure and water content, on the one hand, and upon the
rate at which it receives water from lower tissues on the other.

DAILY COURSE OF LEAF TEMPERATURE.
METHOD.*

The method to be described is one commonly used by physicists in the
determination of specific heat, heat of evaporation, etc., the underlying
| principle being that when two substances at different temperatures are
- placed in contact and external loss or gain of heat is eliminated, the amount
of heat gained by the cooler body is equal to the amount lost by the
’ warmer one. Or, expressed more concretely:

(A) (Sa) (Ta— Tc) = B(Sb) (Te—Tb)+C(Te—Tb) (1)

where

A

weight of substance at the higher temperature.

B = weight of substance at the lower temperature.
Sa = specific heat of substance A.

Sb = specific heat of substance B.

Ta = initial temperature (centigrade) of A.

Tb = initial temperature (centigrade) of B.

Tc = final temperature (centigrade) of the mixture.

C = number of calories required to raise calorimeter 1° C.

In the problem under consideration Ta, the unknown required, can be calcu-
lated since all the other factors can be found.

The finding of a substance with which to bring the leaf in contact offered
some difficulties. An ideal substance would have to answer the following
conditions: (1) a liquid in which the leaf may be completely immersed,
which will come into intimate contact with the surfaces of the leaf, and will
penetrate to the interior; (2) a material of low specific heat and low density,
so that small differences of temperature in leaves may register large changes
in a small amount of liquid; (3) a non-volatile material, in order to avoid

 

*A preliminary announcement of this method was made in the Johns Hopkins Univ.
Cir., Feb. 1912,
LEAF TEMPERATURE. 51

errors from loss of weight by evaporation while the experiment is in progress;
(4) a substance which when mixed with water shows no temperature
changes (the high water content of most leaves makes this important); (5) a
substance which is miscible with water; (6) a substance with which sub-
stances in the leaf produce no chemical changes accompanied by heat; (7) a
substance obtainable in the market at a reasonable price; (8) a good con-
ductor of heat, in order that the final temperature may be reached quickly.

This ideal substance has not yet been found, but there are several mate-
rials which satisfy most of the important conditions. Water, the substance
most commonly used by physicists in work of this kind, is ruled out by the
first condition, as it collects in drops on the surfaces of hairy leaves, leaving
bubbles of air on the leaf which will act as non-conductors of heat. The
second condition also helps to rule out water. The third condition might
be overcome by using a large enough quantity to reduce to a minimum the
percentage of error from evaporation were it not for the fact that the specific
heat is so high that a large amount of water requires a larger amount of
leaves than it is practicable to use in the case of small-leaved plants. Alco-
hol answers all the conditions with the exception of the third. It is so
volatile that troublesome precautions would have to be taken to avoid a
very appreciable error. Common glycerine causes a rise of temperature
when mixed with water and therefore can not be used.

Turpentine, the substance used in the following experiments, was found:
(1) to penetrate the leaves immediately, so that they appeared “cleared”
under the microscope; (2) to have a satisfactory combination of specific
heat and density for the use of small amounts; (3) not to be more volatile
than the accuracy of the other factors in the experiment as a whole required;
(4) to show no temperature change when mixed with either large or small
amounts of water; (6) to cause the release of no measurable amount of
heat when the leaves of three species of plants were immersed in it; (7) to be
easily obtainable in the market at a reasonable price; but samples from dif-
ferent distillations show variable specific heats; (8) to have a high enough
heat conductivity for equilibrium temperature to be reached in 2 or 3 min-
utes. Turpentine is thus seen to answer fully all of the conditions except
the fifth and seventh. In regard to-the fifth condition it was found that
although turpentine does not mix with water, yet.the absence of small
bubbles under the microscope, when the leaves used had been immersed
in turpentine, led to the assumption that no air-spaces of sufficient size to
influence the results existed. As for the seventh condition, the disadvantage
arising from the irregularity in the specific heat of turpentine can be over-
come by a little extra labor, for the specific heat can be determined accu-
rately to the second decimal place with the apparatus used in the rest of the
experiment or with an ordinary double calorimeter. Samples taken at
various times from the same purchase show an agreement in specific heat,
52 TRANSPIRATION IN A DESERT PERENNIAL.

and so if sufficient quantity be obtained at the beginning of the experiment
to last for a set of readings the specific heat need be determined but once.

Loss or gain of heat from the surrounding air by the vessels may be pre-
vented by two methods: (1) By surrounding the vessel with a non-conducting
_ material; (2) by cooling the liquid to a temperature the same number of
_ degrees belowroom temperature that the final temperature will reach above
room temperature, thus eliminating the error on the theory that the heat
lost to the air is equal to the heat gained from the air in the same length of

 

 

 

 

 

Fic. 24.—Apparatus for determination of leaf-temperature.

time. The latter requires a previous knowledge of the temperatures and
amounts, and this is wasteful of leaf material. The former method is
difficult to carry out in its ideal form, but by keeping the temperatures near
air temperature, and the use of a predetermined “curve of cooling,” very
accurate results may be obtained with well insulated vessels.

The apparatus used was made for the purpose and is merely an adaptation
of the ordinary calorimeter with a jacket. From fig. 24 it will be seen that
the apparatus consists of a calorimeter suspended nearly to the bottom of a
LEAF TEMPERATURE. 53

silvered Dewar vacuum beaker. The calorimeter cup is made of very thin
copper, nickel-plated, and polished to a bright surface on the outside. A
wooden cover, with holes for thermometer and stirrer, fits snugly in the top,
while around the outside is a wooden rim which fits closely to the sides of the
beaker, giving no chance for entrance and exit of air. This wooden rim is
suspended from the top of the Dewar beaker by means of metal wires.
Nowhere does the calorimeter cup touch the beaker or the metal wires.
Cotton is used for a cover at the top, as an extra precaution. A certified
one-tenth degree thermometer was used in the experiments.

That the apparatus is well protected from exchange of heat with the sur-
rounding air, when temperatures within 5 degrees of the outside air are used,
may be seen from the fact that when the calorimeter cup was filled with
turpentine at 5 degrees below air temperature, then put in its position in
the beaker and left in the sunshine in August for 15 minutes, a rise of only
0.2 degree occurred. Further, the regular rate of warming or cooling, as
indicated by all the experiments, showed that a curve of cooling could be
depended upon for use in the small ranges of temperature which obtained
in the experiments.

In order to find the temperature of a leaf by immersing it in turpentine,
the following quantities must either be known already or must be found:
(1) the specific heat of the turpentine used; (2) the amount of heat absorbed
by the calorimeter; (3) the specific heat of the leaves.

(1) The specific heat of the turpentine was determined according to the
customary method followed by physicists of using a double calorimeter of
capacity of over 500 c.c. Three determinations were made which differed
in the third decimal place only, results being 0.409, 0.410, 0.411.

(2) The amount of heat absorbed by the calorimeter system was de-
termined as follows. The calorimeter cup with thermometer and stirrer
in place was filled with a weighed amount of turpentine to a marked
level, this marked level being used subsequently as a guide for the level
of the liquid after the leaves were put in. The vessel with the turpen-
tine was cooled to about 12°C., then weighed and put in place in the Dewar
beaker, where it was allowed to come to partial equilibrium. When the
rate of warming had slowed down to about one-tenth degree a minute a
weighed amount of turpentine at air temperature was quickly added, the
mixture filling the vessel about three-fourths full. The exact temperature
of each liquid was taken immediately before the mixing. The cover was
instantly replaced and the mixture stirred gently and continuously. The
time of the transfer occupied 2 to 5 seconds. The time and temperatures
were then read at intervals of half-minutes until equilibrium was reached
or until the rate of change equaled the rate of change which had been
previously shown to exist for the temperature obtaining.

(3) In order to determine the specific heat of the identical leaves used each
time and to get them in the same condition in which they were used for the
54 TRANSPIRATION IN A DESERT PERENNIAL.

temperature determination, 7. e., in the turpentine, their specific heat was
determined last; meanwhile readings for their initial temperature were taken
as follows.

Turpentine at air-temperature was placed in two calorimeters and the
whole allowed to come to equilibrium on a shaded stand near the tree to be
used. Leaves were quickly severed from their twigs by means of wooden-
tipped forceps and then placed on white glazed paper, from which they were
transferred with all possible speed to one of the calorimeter cups, the other
being kept for a control. The contents of both calorimeters was kept in
constant slow motion by use of the stirrers. Temperatures were read every
half minute before and after the introduction of the leaves.

A determination of the specific heat of the leaves was made by heating
turpentine to about 30° C., then placing it, in the same careful way as above,
into the turpentine and leaves just used in the temperature readings. Tem-
peratures of the contents of both liquids were taken accurately just before
and after the mixing. The specific heat of the leaves was calculated from
the equation,

[A (Sa) +L(Se) +C][Ta— Tc] = B(Sb) (Te— Tb) (2)
where

A=weight of turpentine containing leaves.
B=weight of turpentine added to A, and leaves.
Sa, Sb=specific heat of turpentine.
L=weight of leaves.
Se=specific heat of leaves.
Ta=initial temperature of A and L.
Tb =initial temperature of B.
Tc=temperature of mixture.
C=heat equivalent of the calorimeter.

After the value of Se had been found it was substituted in the equation
[A(Sa)-+C] [Ta—Tc]=L(Se) (Tc—Tb) (3)

where
A = weight of turpentine prepared to receive leaves from the plant.
L=weight of leaves.
Ta= initial temperature of turpentine.
Tb =initial temperature of leaves.
Tc=temperature of mixture.
Se and C=same as in previous cases.

Since Tb is now the only unknown quantity in equation 8, the original
temperature of the leaves can be easily calculated.
LEAF TEMPERATURE.

Following is an example of the calculation for one determination.

TABLE 22.—Temperature readings for the determination of leaf-temperature.

 

 

 

 

 

 

 

 

 

 

 

READINGS FOR LEAP-TEMPERATURE, EQUATION 3.
Calorimeter C. Calorimeter 7. | oie
ir
: temperature.
Time. Temperature. Time. ‘Temperature.
|
{
Cs oe:
10> 59" a.m. 18.58 106 50.5™a.m. 18.32
lL 1) a.m, 18.58 MW 10.5 am. 18.32
Open-d for
1 min.
11h 12™ a.m. 17.58 11 12.5 a.m. 18.32
11 30 a.m. 18.58 11 30.5 a.m. 18.32
12 22 p.m. 18.70 12 22.5 p.m. 18.46
12 23 p.m. 18.70 12 23.5 p.m. 18.46 obese
12 24 p.m. 18.70 12 24.5 p.m. 18.46 it
12 25 p.m. 18.70 12 25.5 p.m. 18.46 19.0
Leaves put in.
12h 26m p.m. | 18.90 12 27. p.m. 18.46
12 26.5p.m. 19.10 12 28.5 p.m. 18.46
12 28 p.m. 19.16 12 29.5 p.m. 18.46
12 29 p.m. 19.19 12 30.5 p.m. 18.46
12 30 p.m. 19.20 12 31.5 p.m. 18.46
12 31 p.m. 19.20 12 32.5 p.m. 18.46
12 32 p.m. 19.20 12 33.5 p.m. 18.46 i
12 33 p.m. 19.20 12 34.5 p.m. 18.46 !
12 34 p.m. 19.20 12 35.5 p.m. 18.46
12 35 p.m. 19.20 12 36.5 p.m. 18.46
12 37 p.m. 19.20 12 37.5 p.m. 18.46 wiki
12 40 p.m. 19.20 12 40.5 p.m. 18.46 seat
12 50 p.m. 19.18 12 50.5 p.m. 18.47 19.0
READINGS FOR SPECIFIC HEAT OF LEAVES, EQUATION 2.
2-6. 2.
1h 18™ p.m. 15.13 1 18.5™ p.m. 15.10 sR
1 19 p.m. 15.13 1 19.5 p.m. 15.10 sacs
1 20 p.m. 15.13 1 20.5 p.m. 15.10 sae
1 22 p.m. 15.18 1 22.5 p.m. 15.10 17.7
Turpentine B
put in.
1b 24” p.m. 21.60 1 24.5 p.m. 15.10 bss
1 25 p.m. 21.60 1 25.5 p.m. 15.10 shin
1 26 p.m. 21.60 1 26.5 p.m. 15.10 17.7
1 40 p.m. 21.55 1 40.5 p.m. 15.15 spt
1 57 p.m. 21.35 1 57.5 p.m 15.20 18.8

 

 

Readings for leaf-temperature determination (equation 3).

Weight of calorimeter C, stirrer, thermometer, etc
Weight of C, ete., plus turpentine A

.. Weight A

Weight C plus A plus leaves
.. Weight of leaves
Temperature Ta

Temperature T'c....

Temperature of air

Weight C, plus A, plus leaves, plus turpentine B

.. Weight B

Readings for specific heat of leaves (equation 2).

Temperature Ta.........
Temperature 7'c....

Temperature Tb............
Temperature of air...

141.74

158.48 gm.
14.51
15.30°
21.60°
28 .84°
17.7°

55
56 TRANSPIRATION IN A DESERT PERENNIAL.

Proper substitution in equation 2 gives:

[(20.66) (.41) + (2.23) (X) +6.80] [6.3] = (14.51) (7.24)
.". specific heat of leaves, X =.64.

Proper substitution in equation 3 gives:

[(20.66) (.41) +6.80] [.50] = (2.23) (.64) (X) .". X=5.3.

ee
Therefore the temperature of the leaves was

19.2°-++5.3° =24.5°, or 5.5° above air-temperature.

EXPERIMENTATION.
EXPERIMENT XX,

A series of leaf-temperature determinations was made from trees D and E.
The samples were taken every 2 hours, a period of 2 to 3 minutes elapsing
between the cuttings. The general appearance of the trees indicated that
tree H was nearer the stage of dropping its leaves than was D.

TaBLE 23.—Temperatures for leaves from two trees with the corresponding air-temperatures

 

 

 

Experiment XX.
Temperature. Difference from air.
Date. Time.
D EB Air. D E
1912. °¢, °¢, °C,

Sept. 16... 9500™p.m.| 26.7 27.6 27 -1.3 | +40.6
11,59 pm.| 22.9 24.8 s 25 —2.1 | 0.2
Sept.17...) 5 00Ta.m.| 19.6 16.0 | 20° 19° -0.4 | -3.0
8 OOfam.| 22:8 24.3 | 25.5 248 | -2.7 | —0.5
10 00ja.m.| 32.9 35.8 33.5 —0.6 | 42:3
12 00 m. 45.9 44.6 37.5 48.4 | 47.1
200 p.m.| 38.0 43.7 pen -1.0 | +417
400 pm.| 35.1 35.9 | 39.5 390 | -44 | -3.1
6 00 p.m.| 29.1 27.9 32.5 —314 | 4/6

 

 

 

 

 

 

 

 

 

 

 

 

9 12 : e s 9. 06 4 a i 2 ss 4 es
Fic. 25.—Graph for leaf-temperature from two adult trees, plotted with air-tempera-
tures. Exp. XX.
LEAF TEMPERATURE. 57

DISCUSSION.

From an inspection of the leaf temperature curves in figure 25 it is seen
that in spite of small hourly differences the two trees show much the same
behavior as compared with the air temperature. In general the tempera- \
ture curves for the leaves are below the air temperature curves at night —
and in early morning until about 10 o’clock, when the lines cross the air
temperature lines and then remain above until some time between 12 and
1 o’clock, when’ they again cross and go below air temperature. When
compared with the water content curves, no actual hourly relationship
appears, there being merely the general relationship that the lowered water
content during the day is accompanied by a rise in the leaf temperature.
Since both humidity and temperature enter into evaporation control and
since the amount of heat received from the sun and air is accumulative,
too many factors must be considered to make conclusive deductions. The
unknown factor is the balance between the heat received and that used in
evaporation. The increase of transpiration for the morning does not keep
pace with the increasing amount of heat energy received, and hence it is
to be expected that less of the heat received by the leaves would be used
by the water in evaporation and therefore more would be available for
raising the temperature of the tissues. The rise in leaf temperature shows,
at least, that transpiration and relative transpiration are not lessened during
the middle of the day because the sun’s energy is being used in other ways,
i. é., in photosynthesis, for the heating of the tissues shows that there is
heat energy to spare.

It will be noted that the leaf temperature begins rising above the air
temperature about the time the closure of stomata commences, and begins
sinking with the opening of the stomata. While the above temperature
curves show no conclusive evidence of a connection with the dip and rise in
relative transpiration in the morning, they present no negative evidence for
the application of the theory of drying, since the ratio of the energy received
to the amount of evaporation can not be determined. It is interesting to
note that the lowered evaporation rate during the middle of the day is not
great enough to keep the leaf temperature down to air temperature, and
that, while there is some evidence of the desiccation theory, the unknown
amount of accumulated heat energy makes this evidence inconclusive.

DAILY COURSE OF TRANSPIRATION UNDER CONDITIONS OF HIGH
AND LOW EVAPORATION.

If the occurrence of the dip is caused by a failure of the ratio of water
supply to demand, to equal unity, then on a priori grounds a plant showing
the dip under conditions of high evaporation either ought not to show it
at all under conditions of low evaporation or to a much less extent. This
was tested to some extent in experiment VIII, where a plant which had
previously shown a dip was run in a room of the laboratory. Although
the plant showed no dip under these circumstances, the absence of sunlight
58 TRANSPIRATION IN A DESERT PERENNIAL.

makes the experiment inconclusive in this respect. Indeed, if the cause of
the dip is connected with the rate of production of metabolic water, the
presence or absence of sunlight would be a disturbing factor. Consequently
another experiment was planned in which the same plant would run under
natural conditions of low humidity and sunlight at one time, and at another
time in the sunlight, but under conditions of high humidity.

METHOD.

Although potted plants have been seen to show the dip much less pro-
nouncedly than trees, nevertheless the impossibility of getting the entire
tree under controlled conditions made the use of potted plants.seem neces-
sary; so in September 1912 another attempt was made to obtain trans-
planted seedlings. A dozen or so plants, varying in age from two to fifteen
years, were very carefully removed from the soil and transferred to pots.
These were placed in the green-house, where they remained until March 1,
when the two surviving ones were transferred to the roof of the laboratory
and there left until the time of the following experiment.

Aluminum shells of the type devised by Ganong* were used to seal the
pots. The tops of the pots were first sealed with plastocene, over which
was fastened a rubber sheet, according to Ganong’s instructions. Since the
plants lose only a small amount of water per hour, the aluminum shells
with their rubber tops made the danger of error from dust particles much
less. Before each weighing the shells and rubber were dusted off with a
camels-hair brush. The balances used were sensitive to milligrams, but
readings were taken only to the nearest 10 mg.

EXPERIMENTATION.
EXPERIMENT XXI.

The subjects of this experiment were two potted plants, Nos. 6 and 7,
whose previous history is given in a former paragraph. The plants were
sealed on the night of April 1. Plant No. 7 was given water immediately
before being sealed, and No. 6 had received no water for two days.

On April 2 the two plants with two atmometers were placed in an exposed
position near the laboratory and the hourly rate of transpiration was meas-
ured. Each plant with its atmometer was carried into the laboratory for
the weighings, care being taken each time to return plant and atmometer
to their original positions in the open. During the entire morning the sky
was partly cloudy and the sun was intermittently obscured. The wind
velocity was extremely high all day. The results appear in table 24, where
the numbers given are the actual losses from the plants, since the area was
not obtained. An examination of these results shows that No. 6 had an
early drop in both actual and relative transpiration, which was followed by

*Bot. Gaz., 41, 212, 1906.
TRANSPIRATION UNDER CONTROLLED CONDITIONS. 59

a lessening in the rate of decrease but not by an actualincrease. The occur-
rence of the maxima of actual and of relative transpiration was 4 and 6
hours, respectively, before the time of maximum evaporation for the day.
No. 7 behaved differently in that its maximum of actual transpiration coin-
cided with the maximum for evaporation and no tendency toward a break
in the acceleration appeared. The maximum for relative transpiration
occurred four hours earlier than the transpiration maximum, and while a

TaBLE 24.—Transpiration under three different evaporation conditions. Experiment XXI.

 

 

 

 

 

 

Plant No. 6. | Plant No. 7.
Date. Time. E a. er. te Teper: Humidity. Remarks.
ae Ps ae
| oF, p.ct.
Aprill...) 708 p.m. | .... |... J eee set ase Bean bye Cloudy. Wind high,
leaflets open.
April 2...) 6 30 a.m. | 1.99 | 0.07 | 0.035 | 0.05 | 0.025 | 64.5 60
9 038 am. | 2.28] .24| .105| .24 "103 | 66 58 Sunlight intermittent.
* Leaflets, 35°. N>
change in conditions.
10 05 a.m. | 3.37 47 | .189| .49 | .145 67 57
11 05 a.m. / 4.52 | .387 .086| .55) .122 68 55
12 05 p.m. | 4.58| .37) .081 .58 | .127 72 50 Do.
2 20 p.m. | 5.44 31 .057 | .60 110 72.5 50
3 55 p.m. | 4.97 | .28] .056] .29|] .058 aes 48 Do.
*7 15 p.m. | 4.28} .20] .047| .24) .056 ite ae 62 Dark at close.
Apriless. |) 1G) -4B sate) acsseee || sneer os sare flees. | rene : a
8 10 am. | 2.11} .18} .085 | .18] .085 53 50
9 05 am. | 2.21) .89| .176| .32|) .145 61 48 Leaflets about 20° apart
s after 7 a.m.
10 05 a.m. | 2.48 40 161] .41 165 70 46 Sun bright and air almost
still all day.
11 05 a.m. | 3.19 35) .110| .55 | .172 73.5 42
12 05 p.m. | 3.80 44) .116) .61 161 79 40
1 30 p.m. | 4.53 44) .097|! .66| .146 88 35
*2 35 p.m. | 4.58 44) .096| .63| .138 88 35
4 15 p.m. | 4.52 39) .086| .55 | .122 36
spiah alt 7:15 p.m. | 3.02 38] .126/ .29| .096 77 38 5 bricht all 4
rill... Sun__ brig’ a ay.
Py § 36 Bet a) aa ea | ae | ao Sane - Moist chamber pro-
a.m. | 1. ‘ f cidaye [eens nat ae tects plant and atmom-
9 06 am. |1.15| .01 $009.) 5e.2dece Il so ssees 55 70 eter from full force of a
10 03 a.m. | 1.26) .08{| .063] ....]..... 55 80 strong wind
11 04 am. | 1.49] .12] 081] ....) 22... 56 80 Leaflets 160° apart until
7 4 p.m., after which 90°
, apart.
Ti BO Sees F18N P|) 092 | sees | sees 58 85
12 58 p.m. |} 1.40) .14] .100] ....{ ..... 58 80
2 08 p.m. {| 1.40| .17| .121/....)..... 65 75
4 07 p.m. {1.05} .10] .095]....]..... 65 50
: 7 30 pm. !3.98/) .19| .048] ....] ..... 70 50
April ll...) 7 45 am. jo... | ose | eee ee ee eas ‘ts . ;
8 55 a.m. | 4.96] ....] ..... -50 | .101 71 35 Sun bright and wind ve-
: locity very high all day.
9 49 am. | 4.10] ....]..... .63 | 154 72.5 32
10 57 a.m. | 5.48) 2... | ....- 75 | 138 74 30 Leaflets 10° to 15° apart
during period of experi-
ment.
| 11 53 a.m. | 5.68] ....) ...-. 82) 144 80 27
' 12 52 p.m. | 5.91 82} .139 83 24
2 00 p.m. | 6.04 90} .149 83 22
4 00 p.m. | 5.86 87 | .148 81 22
7 27 p.m. | 3.58 51 | £142 23

 

 

 

 

 

 

 

 

 

 

drop and rise occur in these rates it will be seen from a comparison with
the transpiration and evaporation rates that they are caused by a decrease
in the evaporation rate which is not followed by the plant, and hence that
this dip and rise are in no sense the kind under investigation in this paper.

The intermittent cloudiness of April 2 made it advisable to repeat the
experiment on a clear day, and consequently this was done on April 4.
60 TRANSPIRATION IN A DESERT PERENNIAL.

The seals of the pots were not broken in the meantime. This day proved
to be continuously clear, with practically no air movement. The results
appear in table 24. No. 6 showed a drop and rise in both actual and relative
transpiration, being of much less magnitude in the former case than in the
latter. No. 7 behaved very much as on April 2, the maximum for actual
transpiration coinciding with that of evaporation, and the maximum for
relative transpiration occurring earlier. .

 

ee

 

 

 

 

7 aS wb i wb Tt @ #@ 4 8 6
Fic. 26.—Graphs for transpiration of plant No. 6, under
two different conditions of evaporation. Exp. XXTI.

Under conditions of high evaporation thus far, No. 6 has shown a morning
drop and rise and No. 7 has not. The next plan was to put No. 7 under
conditions of still higher evaporation and No. 6 under conditions of lowered
evaporation. On April 11 the natural conditions provided greater evapo-
ration than was obtained on either of the previous days, as the sun was
bright and the wind velocity extremely high during the entire day. In
order to secure the desired conditions for No. 6, a wooden box large enough
to hold plant, atmometer, a Lambrecht’s polymeter, and a thermometer
was lined with wet towels; an opening was left in the side and top of the box
for the entrance of sunlight and air. The towels were wet frequently and
TRANSPIRATION UNDER CONTROLLED CONDITIONS. 61

the box was turned as the day advanced, so that no shadow ever fell on
plant or atmometer. The rapid evaporation caused an unavoidable lower-
ing of temperature within the box. The polymeter had to be so placed that
the humidity readings are probably a little too low.

 

 

 

 

 

 

 

o a“ Base for T & E Apr. 11
—_

Base for T & E Apr. 4

7 8 9 10 ol 12 1 2 3 4 5 6

Fic. 27.—Graphs for transpiration of plant No. 7, under
two conditions of evaporation rate. Exp. XXII.

These results also appear in table 24. They show that the evaporation
conditions for No. 6 were greatly reduced and that the actual transpiration
was greatly cut down. The maxima for both relative and actual transpira-
tion are coincident with the evaporation maximum. Thus, without doubt,
the drop and rise do not occur under the conditions of lessened evaporation,
but dooccur in this same plant under more strenuous evaporation conditions.
In the case of No. 7, the evaporation conditions were more severe than
on April 4, but the difference is by no means so marked as was the case with
No. 6. The actual transpiration amounts are higher than before, showing
that the plant was capable of giving off more water than on April 4, but the
relative transpiration is on the whole lower. Furthermore, a flattening of
the curve of actual transpiration occurs between 11 and 1 o’clock, and the
relative curve shows a corresponding dip and rise. Evidently the limit of
62 TRANSPIRATION IN A DESERT PERENNIAL.

maximum water loss for this plant, under the existing conditions of soil
moisture and water content of tissues, is being reached, and it is probable
that the more severe conditions of midsummer would cause a more pro-
nounced drop. It will be noted that the maximum transpiration amount of
No. 7 on April 11 seems to bear somewhat the same relation to its limit as
does that of No. 6 on the same date, although the evaporation conditions
were very different. The facts that No. 7 received water just preceding the
sealing and that No. 6 had been without water for 48 hours make these
results agree in a general way with the results of experiment X.

DISCUSSION OF LITERATURE.

Lloyd* has taken simultaneous readings of transpiration, evaporation,
water content of leaves, and stomatal movement, but, while his read-
ings doubtless answer satisfactorily the question which he had in mind,
they are of no avail for discussion in this paper-because of a haziness in the
sky which he records as existing between 8 a. m. and 10 a, m.

Livingston and Brown,} find in general that green plants, in the desert
of Arizona, “exhibit a marked fall in foliar moisture content: by day and
a corresponding rise by night,’’ and they give as the probable cause of this,
“incipient drying brought about whenever the ratio of water loss to water
supply in the leaves is rendered less than unity.’”’ Unfortunately the above
paper had not appeared when the greater part of the present work was carried
out, and so it could not be taken into account in the planning of the experi-
ments. Livingston and Brown have evidence which leads them tosuggest that
small-leaved xerophytesshow a “higher water content by day than by night.”’
The present work shows that this is not true in the case of Parkinsonia, for
in addition to the hourly curve of leaf moisture given, three different tests,
made on trees on different days, show the lowest daily water-content at mid-
day. On the whole it may be said that the present paper offers additional
evidence for Dr. Livingston’s theory of ‘incipient drying” of leaves and
shows that the same phenomenon takes place also in stems.

 

* Lloyd, F. E., The relation of transpiration and stomatal movements to the water
content. of the leaves of Fouquieria splendens. Plant World, vol. xv, p. 1, 1912.

7 Livingston, B. E., and Brown, W. H., Relation of the daily march of transpiration
to variations in the water content of foliage leaves. Bot. Gaz., vol. Lim, p. 311, 1912.
SUMMARY. 63

GENERAL SUMMARY.

(1) The relative transpiration rates of the plants used differ according to
the previous environmental history of the plant; so that conclusions regard-
ing the actual transpiration rates of plants in sttu can not be drawn from the
measurement of water losses from potted plants. Different branches of a
single tree differ in relative transpiration rate no more than do the relative
transpiration rates of the same branch on different days, and, furthermore,
relative rates of different branches agree as well as do the rates of different
potted plants taken on the same day or the rates of the same potted plant
on different days. Therefore the transpiration behavior of an adult tree
may be known better from the measurement of small branches than from
the measurement of potted plants.

(2) The maxima for relative transpiration of potted plants of Parkinsonia
microphylla were found to vary directly with the soil moisture, and slight
evidence was obtained for the same variation in the case of plants in situ.

(3) The maxima of relative transpiration varied with the structure of the
tissues in the order to be expected from their anatomical structures.

(4) The actual transpiration of adult trees and of young seedlings growing
in the open shows a maximum, which occurs 2 to 3 hours earlier than the
maximum of evaporation for the day. This maximum is followed by an
abrupt drop and a subsequent rise, the rise being much more pronounced
in the case of branchesin leaf. This rise is in general great enough to appear
as a rise in the relative transpiration. In the case of green-house-grown
potted plants of the same species the early maximum appears in the relative
transpiration, but not always in the actual transpiration, and a drop appears
in various forms all the way from a distinct drop in the actual transpiration
to only a slight flattening in the slope of the relative transpiration curve.
The early maximum does not appear even in the relative rate when readings
are taken in the shade.

(5) The curve of stomatal behavior follows the relative transpiration
curve in such a manner that the existence of an interrelation is evident.
When potted plants having a soil moisture of 14 per cent and 3 per cent are
compared in respect to stomatal behavior and transpiration, a relation
between the amounts of transpiration and the size of stomatal openings is
seen to exist, but the amounts are not even approximately proportional to
the linear dimensions of the stomatal openings. No conclusions regarding
the action of cause and effect can be drawn from the measurements taken.

(6) Water content determinations of leafless twigs and of branches a
meter distant from the twigs show an inverse relation, while the curve for the
twigs follows the relative transpiration curve. Curves from further deter-
minations of water content of twigs and their leaves show a relation to trans-
piration and relative transpiration curves, from which is offered the theory
that the drop in relative transpiration and in actual transpiration is due to
a slight drying out of the tissues. This theory is further strengthened by
64 TRANSPIRATION IN A DESERT PERENNIAL.

experiment XXI, in which it appears that a plant which shows the dip and
rise under conditions of high evaporation does not show them under condi-
tions of lower evaporation. The water content of twigs and leaves suggests
also a theory for the cause of the rise succeeding une ae which isbased on
Dixon’s theory for ascent of sap in trees.

(7) Parkinsonia trees in sunlight show hourly ci hges in the relative
transpiration rate, the amount of opening of stomata, in water content of
leaves and twigs, and in leaf temperature, and these have evident inter-
relations which are held to be governed by the ratio of the demand to the
available supply of water.

Since, as is well recognized, the transpiration-absorption water-balance is
probably the most vital factor governing the occurrence and distribution of
plants in desert and semi-desert regions, the facts brought out in this paper
are obviously connected with the success of Parkinsonia as a desert peren-
nial. The story of the responses of the adult tree to the coming on of
drought conditions is as follows. First, the leaflets begin closing earlier each
day until finally they remain open only a few minutes at dawn and at twi-
light. Second, the transpiration amount islessened with the drying out of the
soil. Third, the leaflets drop off and later the rachises. Fourth, the twigs and
small branches begin to die until finally, when extreme drought conditions
prevail, whole limbs are lost without injury to the vitality of the plant, and
thus the tree passes through the drought period in spite of the large amount
of evaporating surface still exposed at the time of the falling of the leaves.
In addition to the seasonal responses, the tree has a daily response which
consists in a closure of leaflets, followed several hours later by a lessening
of actual transpiration rate, while the evaporating power of the air is still‘
increasing. This decrease is accompanied by a closure of stomata, a low-
ered water content of leaves and twigs, and a slight rise in leaf temperature.
The drop is followed by a rise, but in general the maximum transpira-
tion is not again reached for that day. That seedlings do not respond so
readily to seasonal changes is to be expected from the size and structure
of their leaves, since these differ little from those of green-house-raised
plants. Seedlings are frequently found in drought seasons with dead leaves
attached, showing that the leaves were killed outright without falling.
Perhaps the more mesophytic type of leaf can not endure the “incipient
drying” to so great an extent as the more xerophytic type found on the
adult trees. It is hoped that the studies now in progress will throw more
light on the variations of transpiration and root absorption with | soil
moisture.

td