_ _ 
 
 PHOTOROPISMS "'I?H--tt03fdeHR<MATTtrXT(mTnnr"TTn^r5' 'AWVOLTOX. 
 
 e. 
 
 . S tr <t*.f*-.. 
 
 +<- /o 
 ANNIE LtAY KURD. 
 
 
 
 Subraitted 3*. partial fulfillment of the requirements 
 for the degree of Doctor of Philosophy. 
 
 University of California 
 
 April 26, 1918. 
 
 /- 
 
 / 
 
OHZBHTATIOBS ABB PHOTOTROPISH8 IB FUCU8 ABB TOLTOZ 
 WITH HDBOCHHOJI&21C LIGHT OF XQUAL IH7HB8ZTZB8. 
 
 ABBIB 
 
 Submitted in partial fulfillment of tb requirements 
 for the degree of Doctor of Philosophy. 
 
 University of California. 
 
 April 26, 1916. 
 
/. 
 
 PHOTOTROPIST'lS WITT T'ONOCTOOMATIC LIG"T IN FUCUS Alii) VOL V OS. 
 
 The -nower of light stimuli to produce orientations an a 
 /$r"opism3 is a phenomenon which has been widely demonstrated in 
 both the plant ana animal kingdoms. ^ot only canfi unilateral 
 direct movements and r rowth out in some srecies o f r'-jnts, name-* 
 ly ^quisetum, Fucus, 90t- Puccinia_,and related forms, it can 
 establish the direction of the first cleavage plane of the ger- 
 minating snore. Since in such cases the cell on the shaded side 
 of the s^ore becomes the rhizoidal cell. the polarity of the 
 
 plant is determined irrespective of gravit.,- . 
 
 In any attempt to discover t e mechanics of such tropistic 
 reactions,the first problem is to find what wave lengths of 
 light are responsible, and to what extent they are a function 
 of the quality of the stimulus/apart from its quantity or inten- 
 sity. This, then, is the purpose 2$*J^ e c 7 E 3ent ' investigation. 
 
 ^f^tL fl^A-jeJLxJl- T% ^fc^t. *>--L#&&i4^tM%*^' ,5^^ SL&brvJL^-'i*) <x*d b ~ 
 
 ^&.,,&f>&fi reviewing trie literature ***H&i[Diological experiments 
 
 ' >^U- *s~.0.i&-. t^CS^rdf 
 
 with monochromatic light one is struck by fehe abaanoo of quauti 
 
 ave records of -either the quality w tne interisity of the ill- 
 umination. -It ia tfr-woll known f;^ct that "Tae ordinary li^ht 
 filters used to obtain rnonochtomatic lig":t transmit not only 
 
 tho^e vive lengths which predo ; iiu . t.t? i i ive t .e color to the 
 
 screen, but rlso othearts of the spectrum .thariresence of 
 can be detected only by a spectroscopic analysis. Vor example, 
 certain results are frequently ascribed to blue light with no 
 record of just what range of the soectrum was used nor what 
 "ave lengths other than the predominating ones were acting. 
 
 'mother source of inaccuracy has been the neglect or over- 
 sight of the great variation in the intensity or quantity of ra- 
 diant energy transmitted by tjie color screens. Biological 
 
.XO^IOV CFiIA BUO'JT MI VOIJ OITAMOHHOOMCT' TTTIW eM 
 
 ; enoiJ'B.Jngi'io sojjboarr oJ iJnrni^B Jrfgil lo i9. r oa orfT 
 ni bs^JBi^anomab \;l9biw nssd earC rfoirfw nonsmonsprq a ei 
 
 " I 
 
 iB'igJ'Blinu nnso ylno Jo; ; .ei oJb^nxx iBmin;- i-ru? d'n^Icr er*3 rf^ocf 
 
 ,eJrislT " o gsios-re SPITOS ni iut rf.twoT: bnB ecfnsmsvom 
 ^i .emto'i bsJelsi briB BinioouT bn." .euou'? .nr 
 lo enslq saavsalo Jeii'J 9r^^ 1o noi^osixb s 
 9i>ie bsbarfa arf^ no IIso arf^ ese^o rloue ni sonic! .9ioae 
 
 1o ^JiiBlog srfJ Ilso iBbiosirfi gnd 1 89Hioo9d gao^e er'.i "io 
 
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 rfoue lo ajini-i'Dy J i9voosifc oJ Jgnig^.^B Y flfi 
 
 / fcl er" ? enoi 
 
 , 
 
experimenters have fot he most part failed to take into 
 
 i 
 
 sideration "he fact that the quantity as well as the quality 
 
 of the light stimulus varies with the different colors and 
 that the former variable must be eliminated before results 
 can be attributed to differences in wave length alonei Quite 
 
 recently (/y/Y )such work has been aone end published with the 
 
 die 
 
 statement thst^ results! are Qualitative -eniy becau-e there is 
 no way of comparing lights of different colors as to amounts & 
 
 ,_ <tC*tx*-^e- /* 
 
 of radiant energj . kowev-er there have been several methods de~ 
 
 A 
 vised by means of which the relative intensity of monochro- 
 
 matic lights van be measured. 
 
 T he first exact work of this nature was done by itniep 
 and Minder C^f). They usea e blue and a red color screen and 
 a green solution with sunlight as the source of light. 
 
 XX>t&4 
 
 The wave lengths to which each/we^e transparent "/ere known;; 
 and the energy behind eacHi was determined ny means of a therme- 
 pile and a, d'Arsonval galvanometer. The interference of the 
 long heat rays w.-is prevented by inserting a water layer in 
 a parallel sided container between tne thermopile and the 
 source pf light. 
 
 Day (/?/( }, obtained light of known wave length by mean 
 
 of a spectfcum from ."ernt Glower^s formed by e carbon 
 bisulfide prisu and cut down by/a diaphragm witn narrow ver- 
 
 tical slits whicn could be adjusted so as to permit any de- 
 
 sired region of tne spectrum to be used. In t-iis adjustment p 
 spectroscope w;-s used to determine the exact range of wave- 
 lengths passing through the plit.in each of the four illumin- 
 attions used, --- red, yellow, gfeen, and blue. He measured 
 intensity of each with a Boys r: diomicromet, er, nd balanced" 
 them by varying the number of glowers employed in the lamps. 
 
 "hus there was one glower for tne red light light, two for the 
 yellow, and three fot the green ajid biue. 
 
('?" J 
 Laurens in an investigation of the reactions of amphibians 
 
 used these sane metnods and the same ^ppnratus for the quanti 
 tave analysis oi - the monochromatic light he u-ed^ ard for bnlanc- 
 ing then with respect to their relative intensity. 
 
 Gross! Ifi2) also used these snrne methods in determining 
 the reactions of Arthropods to raonocnromatic light. 
 
 An instrument has been devised by I'.acDougal and Gpoehr. ( ) 
 which ner-sures the total radiant energy of any light in terras of 1 
 its dissociation effect on a photosensitive substance. This is 
 measured by a galvanometer, "he advantages in the use of this 
 "photoelectric cell" are said to be its extreme sensitiveness t% 
 the wave lengths of the blue end of the spectrum, arid the fact thst 
 
 its action in ligi-t is H raore nesrly that of the organism than that 
 
 v 
 
 of any othor light measuring instruments available. 
 
 There have been therefore three different methods worked ot 
 out for biological experiraentsf or the quantitoive analysis ofi 
 light stimuli; viz., those of Kniep and Hinder, Day, and of 
 
 ^ racUoupiJ and Sooehr. The interesting apparatus of Patte 
 
 add of I.oeb and Northrut) wherebya quantitave measurement of the re- 
 action of organisms subjected to two beams of light of different 
 intensity, is obtained. The measurement is in terms of the angular 
 deflections from an initial path of locomotion. The same methods 
 might be ar^olied to work with colored lights. A quantitative measur- 
 ment of the greater effectiveness of one spectral region over another 
 of equal intensity might be measured by the angular deviation of the 
 rath of a motile organism from a line perpendicular to a line connect- 
 inp the two sources. 
 
All of these methods with the exception of those of i'nien and 
 inder involve special a^^aratus often not easily available. It was 
 aecessaty for fH e -rurroses of this investigation to find a simpler 
 
 of accomplishing the sa-ne results, '"his report therefore is 
 concerned "/ith t'vo rro ultras; first, a means of making th r: intensity of 
 monochromatic light outlined with a act of light filters equal; 
 second, a comparative study of the tronisma obtained with differ- 
 ra nt ''ive lengths when the intensity variable in eliminated. The nar- 
 
 ^henomena chosen for this study are t^ e rower of monochro- 
 matic lights to (I) establish the rolurity of ^ucus sror el incs and 
 :,he origin and consequent direction of the rhizoids; (2) to nro- 
 iuce the negative rhototr -^ism of t 1 n rhizoid; (3) to direct the move- 
 icnt?? of 1r olvox. 
 
 , Ar>raratus and r ethods for Exposure to Monochro- 
 matic Light of Equal Intensity. 
 
 As biologocal science oec ones more exact with the tend- 
 eouce the expression of natural -phenomena to mathematical form- 
 it is obviously essential to define stimuli of all sorts ouant- 
 Ltatively. Indefinaite or incomplete records of light stimuli can 
 10 longer bo attributed to the lack of means of measuring them be- 
 :aune access to a spectroscore ano thermopile make it possible to 
 inalyae any light qualitatively ana quantitatively. 
 

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 u ^o susu yCq pauTiae^op Btm ^c;o puxtfsq XSjeuo 9t{q. 
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 q.t3fT jo aojnos &i[^ s ^^Sftunt tiq.T^ *uoTq.nxos uaaa, 
 
 
 PUB uaajoe joioo pej i ;u eniq .; ,vasn Jwifci ( ) aaput;. pun 
 
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 B-p"8joir^ e.-nebsq. ^iuo 8ATq.(.^TiBnb 
 
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 8q.tri") suoit; i^!?uat OAV.M ut BaouejajjTP o;. pa^riq-pja^f; sq u .0 
 s^insaj aaojaq pa^-jufUTTe eq ^sn 1 8-[qxj>JA .letiijoj at{^ ^em 
 pu saoioo q-uaaajjfp ai^ i{^TM safxuA snimuf^e m^TT 3^ J 
 
-v> u 3'. 
 
 There are two methods for obtaining monochromatic light for 
 biological experiment/S ' . ---the projection of a snectrum upon 
 the yijH/y/i^X organisms or <s of filtered li r -'ht passed through 
 a colo screen. The former i .3 t"ieo etically the tHMrtr for exact ir 
 work but technical difficulties such as the limited dispersion 
 and low intensity make it impractical for 7iany investigations. 
 Light filters of glass are the :r.ost convenient "leans of se- 
 curin,- approximate! oc r ; I LC li't when unilateral ill- 
 
 umination is desired. Ordinary color screens transmit too wide 
 a range of wave lengths for exact T .vork and at present there t 
 are very f w iv';ose lir'it is of sufficient homogeneity .The uest 
 ia the Wratten filter screen, made in London, <"hich consists o 
 of a 1 ' -al-'tine film between two p/lass platesVacDougal and 
 Sr>oehr(l9l7) have described some colored glass screens designed 
 by them for biological work, but the range of wave lengths to 
 which they ar-e transparent is considerably greater than for 
 the Wratten filter. 
 
 In the experiments to be described, seven Wratten light 
 
 filters were used , each of which was fitted as a window in the 
 
 fy 
 
 end of a dak b .x. i-lach transmitted only a narrqw range of 
 
 -ave lengths but all together they embraced the whole of the 
 visible spectrum. The wave lengths to which each screen was 
 transparent ^ev* determined by testing tie lipht transmitted by^ 
 each with a direct wtsion spectroscope with a wave length scale 
 attached. Thus the quality of the light stimulus acting in 
 each box is accurately known. 
 

 iirq. PU use.. ?oj so .lift. PUB ' 
 
 I PSJ w J J <k T suo eM SJSXT 
 
 o joqu- u &Tf: S)UT^J A o-ft 
 
n he source of light oest adapted i'or use with filters for 
 which all the wave lengths of the visible spectrum nre required 
 
 ^-w-vox-^ 
 
 is the electric ?<rc. The advantages of fts use .- ; re, that all 
 
 filters aan be u^ed in each exposure, insuring identical condition? 
 of temperature, constancy of illumination, etc. The disadvantages 
 
 are several. In the first place, the intensity is constantly chang- 
 ing as the carbonslburn and the arc gets longer. r /orse, the lessen- 
 ing of the intensity nay not be the sane for all the wave lengths. 
 In the second place, fluctuations in the current cause large vari- 
 ations in the intensity. In tjje third place, unless an ifafefefa&J- 
 automatically adjusted arc is available, it is necessary to adjust 
 
 the carbons by hand every five to fifteen minutes^, anfl when an 
 eight hour illumination is desired, tt$A entails considerable inconven- 
 ience. 
 
 The dark boxes were 10x13 en. find 8 era. high, in one end ofe. 
 which a hole was cut so that one of the light filters, 6 x 6 cm. 
 might be fitted into it. The boxes were made light tight with 
 
 tightly fitting covers, and were painted black inside to guard 
 
 for uhe cultures 
 
 against reflections within the box. The dishes used were made of 
 
 r\ 
 
 microscope slides cemented together with ainc eement so as to make 
 shallow oblong dishes 7.5x2.5 cm. and 1 cm. deep. It was deemed 
 necessary to use such flat sided dishes in order to prevent posrible 
 complications from reflected and refracted light in the 
 
curving sicleB of * round dieMeo. In order to axrose more - - 
 than one dish **=***& behind each screen B o that none would be 
 
 shaded by* another, a rack was made to fit inside the box with ^ 
 
 cleats projecting inward from the, ends so that three dishes c/culd - 
 
 he elipped into it one above the other.The light .entering through 
 the screen at the end of the box , fell equally on the one exposed 
 sid e of each of the three dishes. The rack containing the dishes 
 could be easily lifted out and carried to the microscope for exam^C 
 ati on without dicing the ,^^ ^^^-^^ 
 
 The spectrosccpic analysis of the light passing the screens 
 determine, definitely the quality of light entering each box. It is 
 at once evident that the quantity or intensity of light behind 
 filte **. plac ed at #*W* equal distances from the source, ^ 
 vari3 3 ,both because the intensity of light transmitted by the differ* 
 ent screens is dif^erent,and because the different colors are not 
 radiated by the arc with equal intensity .This being the case , dif- 
 erences inrf results obtained behind the screens .could not be attri- 
 buted to differences in the ^^^^^^^^^ __ 
 energy of *& colored lights ift^the thermopile and sensitive gal 
 
 vSnometer., The thermopile is very sensitive to tne energy of 
 
 /\ 
 
 any ether vibtations whether they be the longer infra-red or so- 
 called heat rays, or the shorter, actinic rays^of the spectrum. 
 
 The method worked out for ^eliminating the intensity variable 
 in the use of the filters employed for thtsr investigations, consisted 
 in finding the distance * from the light source at which each box 
 with its colored window should be placed in order that the intensity^ 
 
 as indicated by the deflection of the galvanometer when tho opeft- 
 
 the filter 
 Qnd O f- the thermopile was exposed to the light behind & , was 
 
 in each case. 
 
 It seems necessary, on account of the questions which have 
 been raisedjduring .he course of this work, to stsfe here that the 
 thermopile is equally sensitive to the energy of r the red and^he vio- 
 let ens of .he spectrum, and is, therefore, an accurate measure 
 
of the total amount of light acting behind each color screen. 
 
 . ie true ueeauue lEhe difference between hent and light is only a 
 
 -r- ^^ 
 
 ter of wave length. -i^. a truo thtct (the thermopile measures jj 7 in 
 
 terms of the electric current produced by a difference in temperat- 
 ure of the exposed and unexposed junctions; but it does so by vir- 
 tue of the fact that the energy of whatever vibrations fall upon 
 it be thtfy long and therefore heating in their physiological ef- 
 fect or short and therefore only perceived ad light, is converted 
 into heat energy upon being absorbed by the exposed junction of the 
 thermopile. In other words, the ligh- of the blue end of the spec 
 1rum produces an electromotive force much less than that of the 
 infra- red but no less measurable. 
 
 The instrumetfnta ur td in the enejjy calibration of these 
 screens were Si ariffin^T 1 + " table thermopile with junctions 
 of bismuth and Hwrt^SSv and a moderately sensitive galvanometer 
 (d'Arsonval) .^BsdaP electric arc similar to the one later used in * 
 the experiments themselves nas the source of light* The thermopile -** 
 with the open end screened by on,e of ;the lighjt f J.^exp, was / 
 
 exposed to the light until the galvanometer indicator reached 
 a maximum deflection which took, ordinarily^sbout thirty second^. 
 The number of divisions through which the spot of light re- 
 
 ^^j-a^a JU^a-frJL^-ca-fQ *x*/ ~X-i^e, *>-^<*-&e. 
 
 fleeted from the galvanometer mirror.was noted. This was repea't" 
 ed six times and the average deflection recorded. The other 
 filte^rs were then used in turn to screen the thermopile t 
 and thermopile and screen' moved to such ^ distance 'rrom the 
 arc that the displacement^ of the galvanometer &3&& indi- ^ 
 
 cator opt*'* approximately equal. This -rdi3tan.c'was ^.al.so j^^^y 
 for the ui'icnjroGne.d thermopile^ which rerres en red 
 
 the removal of the control from the source. For the experiment 
 the quantity of light used can be varied for the whole set ^ 
 of screens by multiplying or dividing these distances by 
 the same numbervandthe intensity infall the boxes will remain 
 equal. The actual amount o lisht in candlepowers can be 
 
measured by means of a photometer. Then from the law of in- 
 
 * 
 
 verse squares, viz., that the intensity of li<*ht per unit 
 surface varies inversely as the aquare of t^ ft. distance from -B 
 the source , the intensity at any distance from the arc can 
 be computed. 
 
 r 
 
 The calibration oT~nTe\screens was repeated seven times 
 or until satisfactory checks of the distances were obtained. 
 
 some thermopiles of less rapid action than the one used 
 here, it ^/ in impossible to get results oy waiting for 
 the galvanometer indicator to come to a steady fftate.In such 
 a case the deflections produced by exposure to the ligh^'""' 
 for equal intervals of time can be compared. A series of 
 measurements fom five second exposures agreed very well 
 with those obtained by the other mejjthod, 
 
 TABLE SITC'VINr, 
 
 LIGHT FILTERS^) 
 
 ?ROM AN 
 
 TKAlOaTT2DARB EQUAL. 
 
 Filter No. Wave- lengths Color 
 
 70 6600-^-7000 A.U. Red 
 
 71 6200-6800 A.U. Red 
 
 Distance from light 
 320 cm. 
 275 cm. 
 
 72 
 
 5900-6200 
 
 Orange 23( 
 
 73 
 
 5600-5900 " 
 
 Yellow 25( 
 
 74 
 
 5200-5609 " 
 
 Green 28( 
 
 75 
 
 4700-5200 " 
 
 Blue 25( 
 
 76 
 
 4000-4700 " 
 
 Violet 25( 
 
 
 
 \ 
 
 Control 
 
 
 ,'JTe. 34( 
 
 ;e the same" effect it migTTE oe tne resort or a general inten- 
 iy gradiant; if only the blue ligh<; is effective, the problem 
 one of a chemical effect; if only the red it might be assumed 
 
in. TROPIRTIC REACTIONS TO MONOCHROMATIC LIGHT IN FUCUS 
 
 SPORELINGS. 
 
 The power of external factors to determine the polarity of 
 a germinating spore is, without doubt, the power to orient the spin- 
 dle of the first dividing nucleus, if that polarity is established 
 by the direction of tne first cleavage plane. The work on such 
 
 orientations is very, limitedjaml has often resulted in negative resuWs 
 
 / &fy<~MtcJL/$j. ^/S^-iL^f/^^. 
 
 ^kjjito<-JT~-\ ^2-c*u) woril^U**^ o fr gfl S' 9 ' eggs 
 
 ,'/\ -j^r |r - - f* 
 
 -omoryo QJ subjecting *aasQ.o pressure. The spindle parallel to the 
 flattened sides of the egg. This is consistent with Hertwig's theory 
 that the spindle. should form pareifcel to the longer aocis ofl a 
 iding cell. It is conceivable that the power of light to orient <*- 
 tfe* spindle might result from its power to cause more rapid growth 
 
 <-O-^L*^O-v. -v--v^^-^--T -*1*u^-l<"Vl,^ V 
 
 along one axis, with tho rtfeult thayche elongated celljin turn * 
 orients the spindle No such effect of light has been demonstrated 
 
 with animal eg,^s? but in certain pi an ts . vi z . , Equi se turn , Fucus .Pi c- 
 
 o^v^f( C/i<-ocxxw<xOc * 
 
 fystoseira,, it has been found that one-sided 
 'A 
 
 illumination with daylight causes the first cleavage plane to be 
 formed perpendicular to the direction of the incident light and the 
 cell on the darker side of tne spore to become the rhizoidal cell. 
 Equal illumination on all sides retards or prevents germination. 
 Gravity add contact cannot establish the polarity of these spores. 
 
 All these experiments were conducted witr natural light as the 
 source of illumination. The first purpose of the present investi- 
 gation ?/as to determine tne ower of monochromatic light to es- 
 tablish the the polarity of germinating spores of Fucus evanescens. 
 
 It was hoped that the results o4 such experiments might give a clue 
 
 Y> W 
 
 to the mechanics of aZuA orientations. If all wave lengths should pre- 
 
 s\ 
 
 duce the same effect it might be the result of a general inten- 
 sity gradient; if only the blue ligho is effective, the problem 
 is one of a chemical effect; if only the red it might DC assumed th*"t~ 
 

the orientation is due to a metabolism gradiant. The second pur- 
 pose qC&^a study of the photro*ropism of the young rhizoids in 
 monochromatic light. It has been shown (^T^jft that they are neg- 
 atively heliotropicjbut the apparatus designed for the polarity 
 experiments made it very easy to answer^, several questions concerning 
 
 tnyfr phenomenon wore definitely. These questions are:(j) What wave- 
 lengchs are responsible for the turning away from a source of white 
 
 lightt (2) What is the role of intensity of the light or is it a 
 matter of quality alone or both? (3) Do all lights which have any 
 efiect at all produce the same negr tive tropism profluced by white ^ 
 light? 
 
The f irat work establishing the nov: km I fact that one- - 
 
 sided illumination will cause the first division plane of a germinating 
 
 J 
 
 spore to be perpendicular to the direction of the incident light 
 s done by Stahl(/f? $"*) on Equi fee turn. He found th?<t the first wall 
 
 is formed perpendicular to & light rays striking the spores on one 
 side only, and that if ? 11 sides ore illuminated by rotating " 
 
 spore? on a clinostat , the formation of ine vrall is retarded or 
 prevented. The cell on tne shaded side of tne s -ore become? the rhi - 
 zoidalfcell. in darkness the formation of the first v/all follov/s 
 no rule and the rhizoids extend 4n every di ection. Stahl refers to 
 
 enrlier v/ork on liar s i 1 ia and n ara. whicn indicates /I that gravity 
 
 a 
 is ton. controlling factor in the otientation of the first division 
 
 A 
 
 plane 
 
 
 , 
 spore regardless of the light direction. SK ^Je conclude^ that no$T 
 
 A 
 only light but a difference in the concentration of oxygen on the 
 
 two Fides of the spores could determine their pol; rity. He says 
 that as a result of their respiration tne water in the center of 
 the groups of scores is lesn rich in oxygenjand as a consequence 
 the rhizoids^p. are formed on th?>t side. Inlsupport of this theory 
 is the fact th ':. although light can determine the polnrity of all 
 
 
 Rosenvinge(1889) showed that in Fucus spiralia there is no 
 
 relation between gravity and the first division plane nor did con- 
 
 . 
 tacf with a solid body have any effect. He got tne same orientation 
 
 - 
 to light in Ascophylium and ./ucrus' that Stahl did with Bfruisetum. 
 
 but with puzzling exceptions. There the spores were in groups the 
 
 ^k_ /T_xjv-^W - *^ 
 
 cell/ toward the -4e&r, interior of the G r up became; and in the lov/er 
 part of hanging drops the rhizoids appeaWon the upper side of the 
 
/f 
 
 tne specie^- led excet> Vucua serratus ;viz. .Agcojohyllum nodosum. 
 Fucus vesciculosus, J<\ soirniis, n/.d Pexvetia comiii cul r it.p , their 
 sensibility to light differs and the oxygen factor or internal caue~ 
 
 es t&tjS&Bfe?/ produce frequent exceptions in all but Pelvetia. 
 The rhizoids of the latter species are alwa/y sf oraed on the darker 
 
 side of the spore, and this is the one species in which tne egg 
 is surrounded by an oogonial wall which might prevent any of he 
 
 effects of varying oxygen concentrntion^which can net more potent- 
 ly thsn light on the spores of the other species. Rosenvinge quotes 
 
 Kny as finding that neither light, gravity, ijor contract c?t( influ- 
 ence the point of origin of the pollen tube from pollen grains, 
 
 but that in tne neighborhood of other grains tne tubelwill be sent 
 out from t,-.'.e side away from them, on which side the supply of 
 
 oitygen or nutritive elements would be greater. 
 
 -iS^SHSV, farmer and Will iaias ( iS'fv ) state/ that if Fucus spores 
 
 / 
 
 are illuminated on all sides they tend to remain spherical in%tead 
 of producing B rhizoid bu t<:e elongation of one of the two cells. 
 Again(l898) they experimented with one-sided illumination with the 
 usual result that most of .he rhizoids originated on trie shaded side 
 of the spore and the others *fere turned that Iway. The fact that some 
 graw out at an angle to tne incident light 4s attributed to "the 
 character of the egg itself". 
 
 inkler(#//1900) found the some orienting effect of light on 
 tne spores of Cy s t o s e i r a __b ar b a ta but failed to find any dffect of 
 
 a difference in the oxygen content of the -vater. He too 
 
 A 
 
 that gravity and contact are not factors in the establishment of 
 polarity of the sporelings. r.e found that the direction is determin- 
 ed before the firs', division takes place. Since t is polarity is 
 established during the firstjfour hours of illumination and connot 
 changed afterwards by any change in the direction of the incident 
 light, he concludes that light can orient the spore only during 
 fertilization. 
 
- 
 
Randolph and I : ^rce(l905) performed *m one-sided illumination 
 experiments on Sicbyota. JJictyooteris. Lanrencia, and Gystoseira, 
 and poinl^out the certainty of the j^/diium-jy action of other factor 
 
 because rhizoids are formed in .he dark and in all-sided illumin- 
 i 
 
 ation. They say that although Y/inkler (1900) suggest^ tne possibility 
 of stopping germination toy changing the direction of lign-; every 
 three hours, i ; could not be done with Sictyopteris. They emphasized^ 
 theroossibility of influences preceding the illumination affecting 
 tr:e polarity. 
 
 The work of Fronrne'Rev. 1914) on the urediniospores of Puccinia 
 
 rhamnif shauid oa men-. ioned horo/. He *&* that in darkness the 
 
 ^ U 
 
 germ tube grew from any side^oT the spore, but that in inilateral 
 
 e tubes almost always issued from the darker side of the a* 
 spore. 
 
of. 
 
 the first cleavage 
 icus scores. germinated in u**Tlateral have failed so far 
 
 ^L^' _^^ A 
 
 All attempts to solve thi groblera as to wh^tr"wave lengths of 
 
 ;ht are responsible lor the orientation 
 
 \ 
 plane o 
 
 ^^ ^ 
 
 and apparently -aTnvalsucceed^fith the pparatus described 
 
 in the first port of th^>^pape>>*41owever it seems worth while 
 to report t-e metlpyrfs used and why theyhmte failed. T 7ork v/ill be 
 continued on^fenis investigation at the earliest o*pXjrtunity, PS it 
 is mereiar a matter of obtaining the right conditions of "gmjwth 
 
 bejtffnd the light filters, together with a sufficiently strong 
 
 illumination. 
 
 The fruiting plants of Fucus eyanescens were collected at 
 Sausilito at low tide of one day and kept over night in damp news 1 *' 
 
 papers. The next mornibg they were dried slightly by exposing them 
 to the air for about half an hour or less. The fruiting tips were 
 then cut off a'^ submerged in *ta- v/ater in the culture dishes. After 
 fifteen minutes many eggsjand sperms have settled to the bottom of 
 the dish or can be scraped 6ff into the water. The piece of plant is 
 
 then removedVnd the dish is placed in the rack which fits into 
 a dark box behind a filter screen. Each box with its cultures 
 
 is placed at the proper distance from the light so that each is il 
 luminated with equal intensity. These distances for each 
 
 the raethod by which they -'ere obtfii- ed^ 
 
 by five as the case might be 
 
 distance given tnei? however was divided by four or 
 
 ; / *\ 
 
 in order to increase the intensity of the illumination equally 
 
 for all. The illumination with the electric arc was continued 
 
 V ^ 
 
 for eight in an otherwise darkened room, the carbons being ad- 
 
 justed every five minutes. This time was judged more than sufficient 
 
 M*4 
 
 to produce **jseffect since it was found in Cystoseira ( 
 
that the polarity of the egg is so firmly established by four hours 
 
 exposure to daylight that it cannot be changed. 
 
 / The f<ct that Ku cuy^evan es c ens is a monoecious specita 
 makes it impossible to tell the exact time of fertilization, 
 but it occurs soon after the eggs escape from the oogonial 
 sac into the water. The sperms at this time can ba seen 
 escaping fro-n the antheridia and swimming rapio.i./ around the 
 eggs, then scattering as, presumably, one of than succeeds in 
 entering. The first oross-wp.li can "03 seen very plainly 
 twenty- four hours after the cultures are started. The 
 mucilage accompanying the eggs caused them to aether e so 
 firmly to the distil that it is not necessary to use f sol^d 
 media to ke p the sporelings from being displaced when the 
 
 cultures are moved to the microscope sjage for examination. 
 
 However U-Hha eggs germinated behind the color screens^ 
 
 and illuminated for the first eight hours after fertilization. 
 
 - 
 
 showed 4r orientation with respect to the direction of the- light. 
 They grew 'corually as if in darkness with the direction of the clear - 
 age plane following no rule and the rhizoids extending in every dir- 
 ection. Evidently the intensity of the light was too low to have any 
 effect, or the time or duration of the stimulation was not right. 
 
 Attempts to increase the intensity by bringing the cultures closer 
 
 that is. within about seventy-five centimeters 
 
 to the wrcTfre suited invar iably in the death of the spores Before any 
 
 A placed (5"cm. from the naked arc 
 
 development occured. A cooling device^ consisting of a layer of water 
 
 A 
 
 (p cm. thick between two glass plates, reduced the temperature 
 from 29 to v*s*^y-+*^=^fa^^\\\\\'r^,^f^iFrjrtp^/ but al so A r educed 
 che intensity of "#Te light that no orientation was obtained. Attempt* 
 to use direct sunlight as the source of light also caused the rapid 
 death of the eggs, presumably on account of ',he high temperature 
 accompanying it. 
 
 Future work on this puoblem auafr therefore involve the use 
 
 of stronger sources of illumination ajdn cooling devices to 
 
 "-a an ^ 
 
/r 
 
 keep :;he temperature below the death point. 
 
 interesting results were obtained in an experiment to dis- 
 
 #6^4+ 
 cover the weakest stimulus whicu would produce the charact4ristic 
 
 A 
 
 orientations of natural illumination. Cultures were placed at in- 
 tervals of 15 cm. froia an east window a^n exposed 8 hours on a 
 cloudy day> Upon examination a few days later every culture was-te 
 
 found to show strikingly the strong orienting effect of unilateral 
 in 
 
 daylight. Even the one fartherest away, 350 cm. from the window^ were 
 practically all oriented 
 
 c^~4j,* "l^more'dfr lets^/ 
 r ._ivery Culture js nowing this orientaion has.f requent ex- 
 
 ceptions to the rule. Every worker on this problem has reported 
 such exfceptiens and they toave been ex*~plained by the assumption 
 of the existence of an inherent polarity which as a rule i over- 
 come by the stronger light stimulus. The fact that in absolute -fr 
 darkness, germination and normal growth are as rapid or more so 
 than in light, also points 60 an inherent polarity. But the tend- 
 ancy varies enormously in individual spores. Therefore it is easy 
 to understand that slight variations in the quantity and quality of 
 illumination might easily produce'-b*^ changes in the ] sensitiveness 
 of the spore toward light, which ;eans failure of experiments with 
 monochromatic light until the right combination of other external 
 factors in produced. 
 
 It was^oon discovered in the course of this investigation 
 that although the WJLtf intensity of the electric are. used was too 
 low to orient the cleavage plane of the egg and too low to cause 
 the cell away from the ligh , to become the rhizoidal cell, it was 
 strong enough to produce a conspicuous neeative heliotropism of the 
 rhizoids of these same spores if the illumination was resumed after 
 the rhizoids fead develop d- OKly seven hour exposures were used to 
 
obtain this effect. On th^day after s-ich illumination examin- 
 
 ation showed that the rhizoids of th_; cultures behind t 
 
 sharply 
 blue and violet filters were all turned away from the light, 
 
 tff/ltr 
 
 behind -3d*- t. 1 '.^ filters continued in the direction in which the 
 
 jtAAJSs *SQ -4^~~tt 
 
 had started, .anqpoaring no different thair-&aa control in dark- 
 
 * 
 
 ness. Therefore the wave IS-ngths responsible for the neg- 
 
 ative phototroplsm ffi////jiin white lighyare those 
 of the blue end of the spectrum. It should be remembered that -Hi 
 there is no question of a difference in intensity entering here 
 because each screen was placed at such a distance from the arc 
 that the quantity of light in each box qas the same. These re- 
 sults are summarized in the following table 
 
 .. KELIOTROPI S M 
 
 Filter^ COLOR TAV^ L^CGTH? DISTANCE FROM 
 , LIGHT CULTUPES NO. I + J 
 
 70 red 6600-7JOQ A.U. T& <~ . 
 
 71 orange 62^0-6800 ' bff - 
 orange 5900-6200 -rt - 
 
 yellow 5600-5900 fe>2. - 
 
 green 5200-5600 70 
 
 blue 4800-5200 (* % " 
 
 violet 4000-4700 * " + -f 
 
 white tfo<Jo -7000 -/- 
 
 ^L. 
 
 T Ke s e 
 
 A Dlmilar experiment was triedVrth sunligTit; as" the source 
 
 of illumination. The young plants were exposed behind the fil- 
 ters all day in a south window. The same results were obtained 
 as when the arc was used. Then the experiment w :s repeatedwith 
 diffused light. The boxes were placed in an east window fir eight 
 
 hours_ --- 10 A.M. to 6 P.M. --- on March 28. Again the rhizoids 
 
 /i^txz^-d-vt/e-*- 
 in the blue and violet light showed the frrMffiisrii, but in addition 
 
 a considerable but much smaller portion ware affected in the same 
 
 jP J // fJui. c+Ts*s*h<^^> f <*s<-*-<^ -* 
 
 behind the green filter. &******[< , ->J"Jr<7L /' / 
 L ^JLtZ^^eu^^*^ +*&* **^J^* 
 
 waj 
 
 These experiments 'ndicate that the light of wave length 
 
 * 
 
 4ooo-520CWImgstrom yUnitaVf^ responsible for the phenomenon, 
 
 but that some rhizoids, more sensitive, will respond to those of 
 
 5200-5600. It seems very possible in view of the results on 
 
ir olvox reported in the third part of this parer that with a^greater ^ 
 intensity, the rays of the red end of the spectrum might caWse the sane 
 negative phototropism. *&? 
 
 Only the growing tips of the Jifrhizofds are sensitive to light^, 
 m his results in a sharp angular turn if the direction of illumination 
 is changed through 90 or 180 degrees, or if the plants be brought 
 from darkness into unilateral light. As pointed out by Loeb and others 
 tropismJla uncftubljunliy due to the di ference in the speed of the 
 
 chemical reactions going in the two dides of the growing tip. 
 
 T he first protuberance of the germinating spore is not affected 
 by light striking it from th'i side; and if it is so illuminated 
 during the early stage of elongation of this cell, the first bend 
 occurs at the cross wall separating it from the next rhizoidal cell. In 
 
 s~* 
 
 other words, the firs t rhizoidal /^elongation continues in the orig- 
 inal direction established by the first cleavage plane. and the wall 
 separating it from the next cell of the growing ehizoid appears as the 
 axis of the tropism. 
 
 In every culture of Pucus evanescens whether germinated in 
 darkness or in strong unilateral light a most striking orientation of 
 the first cross-wall with reference to adjacent spores appears, ^her- 
 e-teer a group of spores are lying within about 0.2 mm. of each other, 
 the first cleavage plane is perpendicular to the direction of the cen- 
 
 t^er of the group. THe cell toward the interior invariably becomes 
 
 C ) 
 
 the rhizcidal cell. This phenomenon was reported by Fosenvinge in 
 
 --" 
 
 other species of Fucus and in Ascophyllum. 
 
 ^ 
 
 A study of this phenomenon ^pfs madeM'to determine the strength , 
 
 compared to *^'**^' 
 
 of the stimulus producing this effect, **- that of light. in 
 
 A 
 
 A 
 
orientation lu lh ) lUnaaliou of itc rayo.lt was at once very 
 
 evident that for most spores the formal? provaiirs when the spores are 
 within a short distance of eachf other --- .2 mm. or often more --- 
 and beyond this distance, the chemical^) stimulus becomes too weak 
 and only the light is able to determine the polarity of the plant. 
 Only the comparatively isolated spores therefore ever show the orient- 
 ation to light ; i-rrj )i I'JL I'H-iml with the^ource^ of illumination uned 
 
 here. 
 
 The phenomenon is V3ry conspicuous ia groups o"' 2, 3, or 4 
 
 eggs as well as in masses of fifty or a hundred.. In these 1 ,rge ,-roups 
 it is made evident by the invariable rtile that no ;%fl/^/rhizoid ever 
 
 extends outwards from a group. Then two spores are within the distance 
 
 which 
 through the stimulus is effective, the first cleavage planes of the two 
 
 are often parallel and the rhizoids grow towards each other and often 
 meet tip to tip. The groups of five or six often make symmetrical 
 star-like designs when the rhizoids have grown and p/oject beyond the 
 group. 
 
 ""he spores are more rarely affected in thas way when the distano^ 
 between them is over*>.3 mm^but the phenomenon is sometimes observed 
 in spores as much as O.5 mm. apart. Tithin a distance ofo.2 mir.. 
 there are practically no exceptions. 
 
 ^he relative sensitiveness of a sj ore towards light and 
 towards this cherr.ical( ? ) stimulus varies greatly for different 
 spores. "'hen cultutes were placed in the window to get as strong 
 a light stimulus as possible in order to determine at what distance 
 from each other the eggs had to be not to show a greater sensitive- 
 ness towards/the chemical stimulus than towards the light, it was found 
 that^this distance followed no rule, the scores showing the greatest in- 
 dividual differences. Of two spores lying within 0.3 mm. of each other 
 one might be ^entirely oriented by the adjacent sporephile the otherj 
 apparently like it, Would show only the action of the light stimulus. 
 
In many canes two such spores wouljl see- to show a rss-iltant effect 
 of the two stimuli so that both -YOU Id be half turned towards each other 
 with fe*VhlzOidal ceil showing a^tcTtake -a direction away from the - 
 
 oK- iv*~-* 
 
 light at resultant angle. 
 
 T osenvinge ascribes this group orientation to a difference 
 
 d>n the concentration of oxygen or of nutritive substances on the two 
 
 forms on th > side 
 sides of the spore. He thinks the rhizoid^i'/ 4,/V/ 1 / toward 
 
 of a group or towards another egg because the water on that side is 
 less rich" than on the outer side of the spores as a result o,' their 
 
 /\ **u^A. 
 
 metabolism, '"inkier (^ ) working with Cystoaeira barbata^that a dif- 
 ference in oxygen concentration ha? no such effect. Apparently the phe- 
 nomenon does not occur naturally in)thisjspecies since Wwr figure 
 given shows nothing but the effect of light. I have nevor seen a culture, 
 of Fucus evanescenjlth spOres germinating so near each other, which 
 s! owed only light orientation and ::ot the group orientation. aAl- 
 raost invariably when the spores- of this species germinate in such 
 close proximity, lipht appears to have no power to establish the po- 
 larity of the plant. 
 
 The possibility that the group orientation is due to a pol- 
 arity established by the position of the egg in the oogoniura is 
 
 tut*** 
 suggested by finding many groups of lying just as they escaped fror- 
 
 the oogonial sac and conspicuously oriented with respe?t to each 
 other. The fact that groups of ten or of two are as regularly 
 oriented, would refute thT suggestion; but in order to prove that 
 the phenomenon is the resuljr of a stimulus acting after the eggs 
 leave the oogonium, a group of them were transferred to a watch crys- 
 tal and mixed with the point of a needle until their relative posi-fc- 
 
 "/ions were entirely changed. But when they germinated the character- 
 istic orientation with respect to each other was found to be with- 
 out an exception. 
 
m he only apparent explanation of the group orientation is '.hat 
 of a diffusion gradiant of some substance emanati^ng from a growing 
 spore, or of some substance being used up by it. A continuation 
 of the inve/stigati ^n of this problem will b3 an attempt to dis- 
 cover a substance or substances which can so effect the dividing 
 nucleus of the egg cell that its unequal distribution on *M sides 
 of the cell will orient the qxis of the spindle, The effect of bub- 
 bling carbon dioxide or_ oxygen through one end of a culture will 
 be tried as being the most probable factor^ involved. 
 
 A striking phenomenon which seems to be further evidence of 
 the power of a chemical stimulus to orient the spores was found in 
 three different cultures. ?.mall pieces of a foreign substance, 
 apparently sand, caused the orientation of the spores adjacent to 
 astey'ith the result that the rhizoids all extended inward towards 
 t: e substance. This material was present in too small amounts for 
 chemical analysis. A search for some difficultly soluble substance, 
 or an insoluble substance which might be sligBiJfly soluble in the 
 weak carbonic acid produced by the growing spores, which, when added 
 to the cultures , might orient the eggs adjacent to it, has failed 
 to brin* any positive results. They do show ^however, that the phenom- 
 enon is not due to a contact stimulus. "Ehe^//^ substances tried 
 W3repcheelite/ Ca^o^Oj; 'Magnetite/ F Qj J, Ba ite/Ba^So), Casser-ite 
 
 n oAnornblend, tfubellite, beach sand, granite, and silve~r filings. 
 The substance or condition originating in the activity ofacfjacenf 
 
 spores which has so powerful an effect in orientating the first 
 plane and in determining which cell shall become the 
 
 A 
 
 zoidal cell has no power to cause any chemotropism of the rhizoids 
 
 after they are started. No rhizoid has been found to have its direct- 
 Ti on modified by the presence of other spores adjacent to it. In 
 the absence of any light s$imulus)the rhizoids continue in the direc - 
 tion that they take priginally from the spore. 
 
-i-Ct^Yrt/ma/W 
 
 TO summarize briefl" '. .is work on light and chemical stimu 
 li as they affect the polarity of ^ucus e .d the direction of 
 growth of the rhizoida: 
 
 (1) Green, blue, 8$rt violet "-ight (4000-5609 A.n.) of an inten- 
 sity great enough to produce negative phototropisms of the growing 
 rhizoids is without effect on the direction of the first cleavage f 
 plane of the egg. 
 
 3 
 
 ? N 
 > J 
 
 chemical stimulus which orients the direction of the 
 
 first cleavage plane and determines which cell shall become ths 
 
 rhizoidal cell 
 
 alli 
 
 diet 
 
 vhemi 
 
 ' ~-' hrig no power to ^s&r,. c cf 
 
 rhizoids . 
 
 ()Th laxative photctropism or the rhizoicr : . *i .^o- 
 
 .. ~ c ' _ . '. .' , . "^ " .a_. ^ 13 
 
 since, with equal intensity of illumin; ." ;ht 
 
 : peel . Lthoti ^ 
 
 j - 
 
244. 
 
 V. -- Pho tot rop isms ci Volvox in Mono chro 'na tic 
 Light of Equal Intensity. 
 
 Oltraanns ( /?<fR ) , Holmes ( J<p3 ) and Mast have reported in detail 
 the reactions of Volvox to li^t stimuli. No one, however, has studi- 
 ed its response to monocnroraatic illumination. The purpcs of the 
 present study is a comparison of its phototropisrne in different spectral 
 re -ions for which the intensity is made equal. 
 
 The recent article by Mast (l?'7) suns up in a table the litera- 
 ture on the reactions of plants and ini^als to colored light so cc - 
 pletely and so concisely that there is no necessity for a repetition 
 here. ite summarizes briefly results jiven in the table as follows: 
 
 "For seedlings < f gr 5 n plants, plumules and radicles, the 
 region in the spectrum of maximum stimulating effect ia in the blue 
 or violet. For the fungi it is somewhat nearer the red. For Bac- 
 terium pho tour? tri cum it is in the infra-red and the orange. For 
 Oscillaria and Piraiaeoium bursaria is it questionable, activity and 
 aggregation being probably determined by cuemioal changes in the solu- 
 tion associated with the colors. For Chlp.mydomonas it is in the 
 green; for all r ther unicellular forms tested it is in the blue, as 
 it is also for the co^l^nterates and vermes and for a few of the 
 molluscs an.-" 1 Arthropods. >ut for most of the molluscs and arthropods 
 it apcears to be in the ,^re ^n or yellow." 
 
 T -)t tb ? -:if<st effective wave lengths -ir* 3 not the erii.ie for even 
 related forms in the lowr organisms iB furt)ir borne cut by lias Us 
 ( l^l"[) results. u e found that the maximum efficiency is near 483 
 for 3uglena, Tra^relomonas, Phacus, Gonium, Arenicola and Lumbric.s; 
 

25-- 
 
 near 524 /y for Pandorina, Eudorina and Spondylonio ruin; and near 
 503u./^- f or Chlamydoinonas and olcwfly larvae. The wor? of Schaelferf^ ) 
 on amaebae 3 i iteresting as his results indicate that the prwr cf 
 a beam of red light to cause the organisms to move towards it is as 
 great as a beam cf white light, and hae mere attraction than the blu- 
 Most investigators of phc to tropisms find either that the red is less 
 effective than the blue or that it has nc effect. A few find that 
 in equal brii'Jitness, tha effect is nearly the same for all colors, 
 e Volvox colonies upon which the following experiments w~r 
 made wre collected by Dr. N. L. Gardner in a small la>e in Golden 
 Gate Park on April 2, 1918. They we*e so abundant that the water 
 was quite : Tr?n vr ith them. 
 
 On April 5 they were exposed to direct nunlifiht behind the 
 seven Vfrat '.en litfit filters used in the work on iucus. The same 
 rectangular, flat-aided dishes made of microscope slides cut and ce- 
 mented together were used. The disfcss, filled with a Vclvox -us- 
 pension were planed in the dark boxes in one end of e r ioh of wliioh a 
 color sere ?n waa fitted. The series of eight boxes were tnen ex- 
 posed to direct sunli.-jit. A: intervals the covers were raised to de- 
 termine roughly the ^r^ntage of org'inisns reipondinst as shown by 
 the completeness of thei c aggregation. Ths results of Uiis series 
 are surnra-'xrized below, the plus ^i ,hs i :! opting an obvious positive 
 hello tro pi am with Uie org nip-in coll e -ted against the ^lass on the 
 side toward the sun, a 2<=>ro indicnti".; r no ^vidence of any eftect of 
 the light. 
 
--26 
 
 Table No. 1. 
 
 Volvox Reactions to Sunlight behind Wratten Colored Filters. 
 
 Filter 
 
 70 
 71 
 72 
 73 
 74 
 75 
 76 
 
 Control. 
 Table No. 2. 
 70 
 71 
 72 
 73 
 74 
 75 
 76 
 
 Control. 
 
 Wave Length in 
 Angs t r o m un its. 
 
 - 7000 
 
 3~c[ OO (o^OQ 
 5<o oo - y<?o 
 
 4-700 - 
 
 4-066 47OO 
 
 H- o o o 
 
 QO - 
 
 - (c^OO 
 5(0 00 
 
 s'Zoo - ^6,00 
 
 y-ooj 
 
 Lj-Odi) JOOO 
 
 Color 
 
 y ) 
 
 Sxposure 
 
 y ' 
 
 10' 
 
 %o 
 
 T IT 
 
 r IE 
 
 r IT 
 
 o.o 
 
 -1- o 
 
 f- 
 
 o o 
 
 
 
 -f o 
 
 
 
 
 
 CP 
 
 + t 
 
 4- -f- 
 
 r t 
 
 f- + 
 
 4- -f 
 
 t -f- 
 
 i- t 
 
 t + 
 
 t t 
 
 + t 
 
 t + 
 
 4- t- 
 
 + t 
 
 -h i 
 
 t f 
 
 t 
 
 3" ' 
 
 jo 
 
 i sT 
 
 ^ 
 
 _ 
 
 JO 
 
 O 
 
 o 
 
 O 
 
 o 
 
 ' 
 
 
 
 <^ 
 
 
 
 f 
 
 t 
 
 O 
 
 o 
 
 o 
 
 f 
 
 t 
 
 * 
 
 * 
 
 t- 
 
 f- 
 
 -f- 
 
 t 
 
 ,h 
 
 f 
 
 t 
 
 t 
 
 -h 
 
 f 
 
 f- 
 
 1- 
 
 -j- 
 
 -f- 
 
 * 
 
 ^ 
 
 t 
 
 -h 
 
 f 
 
 
 
 f 
 
 f- 
 
 t- . 
 
 Table 1 shows that wave lengths from 4000 to 4700 A. are de- 
 cidedly more powerful in directing the movements of Volvox than are 
 those of the remainder of the visible spectrum, 4700 to 7000 A. U. 
 There is an indication, however, that some individuals respond to the 
 long waves. 
 
 Table 2 shows that the stimulating efficiency of the difierent 
 

27-- 
 
 is dependent on the duration of t;:e exposure. At the -^nd of 
 only three minutes, the organisms of the gren, blue and violet were 
 all over to the brighter side of the dish. At the end of 15 mi-iutes 
 the red, orange and yellow had still oroduced no visible effect. But, 
 after 20 minutes, all but the longest waves, 6600 to 7000 had caused 
 a definite ag regation;and after thirty uinutes,' the effect was se^n 
 benind this r^d screen. 
 
 As striding a? tnis relation of the time factor to the power 
 of light stiumli to produce the phc totropisrn was the difference in the 
 response behind the 'four filters of the green, blue, and violet. After 
 only 3 minutes of exposure the aggregation effect was most marked in 
 the violet, less in the blue and still less in the green. The 
 difference in the appearance of the four disnes was due to the 
 difference in the number of individuals that had responded positively 
 and the completeness of their response, i.e. in 4-0 o-j i+j o 
 practically every colony -va igainst the glass on the outer side of 
 the dish; in A =. *f 9o - frffctf ^- A there were more scattered about in 
 the water. In 5200 - 560^tf still more and in 560 - 590^ 
 
 there wre just barely enough affected to make it evident that some 
 were positively [z?o%4'(l; After 10 minutes this gradiant was still 
 visible. After about 15 minutes, the dishes all looked alike. Tnis 
 again shows the importance of the time factor, since the less sensitive 
 organisms which respond less rapidly are after a longer time afteoted 
 to the sane decree. 
 
 In all the succeeding exposures with sunlight this rule held 
 good, that the organisms behind 76snd75 respond most rapidly and most 
 

 
--2; -- 
 
 crrnpletely , followed "by those "behind 74 and then 73. It WT.S < f oen 
 quite impos ible to detect ny dit'terenoe in the response behind 75 
 and 76. 
 
 It was noticeable in every series exposed that in the -vhite 
 light of the control complete aggregation of the colonies as the re- 
 sult of their phototropism was no*- so rapid as in A=*to f -i^o /*-P- 
 Repeatedly the observation was made that the control locked more like 
 the culture in fr* 1 - VR /+yt^ T:.e expl.-unticn in prob-ibly 
 
 either that the intensity was fso raiich greater that some individuals 
 were caused to respond negatively, or were neutral; or that the great- 
 er reflection from the back of the dish ma e all parts of the watr 
 more nearly ali>-e in intensity of illumination and so tended to 
 equalize the Rtiraulus acting on the different sides cf the orginism. 
 
 When a series of cultures was xpooed in the same way with the 
 sun hidden by clouds no respcns -> could be obtained behind the red, 
 cringe ^nd yellow filters. 
 
 Theae experiments srow the greater stimulating eiticiency of th e 
 blue end nf the apectrura since comparison of the order of efficiency 
 of the screens in produciri/-; the positive response is not in agreement 
 with the order of the intensity of the light behind them, (see table 1 ) 
 In fact the stimuli of least energy produce the most rapid response. 
 They also show that with a longer exposure or more intense stimulus 
 the less effective wave lengths may produce the s-ime degre " of r spons e * 
 In none of the exposures to sunlight were there any negative reactions 
 or reversals of the response. 
 
 On April 6, the experiments ^re repeated -vith the electric 
 arc as the source of li ht, and with the dark boxes at such distances 
 from it that the intensity behind all was the same. The results are 
 
--2S-- 
 
 as follows: 
 Filter 
 70 
 71 
 72 
 73 
 74 
 75 
 76 
 
 Wave -^-'n.- 
 
 (.(.oa ~ "7 & 
 
 b 1(1 O - & % 00 
 
 ac, - *> 
 
 Color 
 
 Distance 
 
 osure 
 
 AJL 
 
 CJ 
 
 + 
 
 H y oo - 5 ' 
 
 ^ 6 ~ Lf -J u0 
 
 - -i 000 
 
 ft. 
 
 r 
 
 r 
 t 
 
 t 
 
 f- 
 
 t 
 
 1- 
 
 The ri.pid reBpcne-- in. t>m re'. v;s aurpriging sinoe the energy 
 must have be-n leea '.han in sunlight. It took 20 minutes to get a 
 noticeable reaction in - Jie orange and yellow in sunliriht the day befor 
 Here with the arc as a source of light it took hut thre minutes. 
 It toc-y 30 minutes to get the resporv e in the red that was produoed 
 by the arc in 5 minutes. The explanation rni^ht be that the 
 colonies were niore sensitive to light nn April 6. It was unfortu- 
 nate that tjiis day vrae oloudy so that the experiment -*ith sunlight 
 o uld not be repeated. That the ability of the colonies to re- 
 spond is dependent to a large extent en their own condition as 
 aflected by external factors of their invironment was shown striking- 
 ly by the fact that organisims kept over night in a small mouth 
 bottle -vould not respond to -my lirjit stimulus, while o th-TS cf the 
 same collection ?ept in shallow pans reacted rapidly. Mast ( 
 found considerable difficulty in ,;etting consistent responses on 
 account of the gre t change in the reactions of . is organisms with 
 Change in their con di lion due supposedly to the li, ht and temp ^r-s 
 oonditons. 
 
30-- 
 
 ism, Also it, J.B prob-'.ble in vi-^w-of jLoab^s -vor>- (1^6 ) that the 
 phototropio reactions of all organisms change with their age. 
 
 Another explanation which was suggested by the fact that 
 white light was often slower in producing a response than the b lue 
 and violet, is that the greater energy of the red in sunlight might 
 have tended to reverse the positive reaction or neutralize it; or it 
 
 ight h-iv* be<?n so reflected within the dish as to act more nearly 
 with the optimum intensity on -<11 sides of the organism. " that 
 as it m ri .y, the fact remains that repeated trials prove Conclusively 
 that at the end of a fiv- minute exposure, all wave lengths of the 
 visible centrum hnve produced equal eft^ots when the source of 
 li; T ht ic the electric arc. This is further proof of Mast's Wf ) 
 contention tir.it: "There ia nc evidenc-- i-.-Mc ting that stimula- 
 tion i-, n.:r; of the 3 studied is independent of lurranous in- 
 
 tensity, for if the light in the spectrum on Cither side of the maxi- 
 mum be made sufficiently intense it becomes iaore efi active than at 
 the maximum, M 
 
 On April 20, another collection of Volvox was made. It was 
 ho r;ed that a rough approximation of applicability of the Roscoe- 
 
 Buns>?n Law in the reactions of th is form U> li :ht. This law states 
 
 ing 
 that o'J<-r conditions "be/eqial, the product of the intensity and 
 
 the duration of the exposure Is .'? co .stant. Owing, however, to the 
 short time required for response and the variations in the sensitive- 
 ness of individuals making it impossible to determine the end points 
 exactly no thin- c ,n be concluded o.s to the truth of this law for 
 Volvox u Li] . nr? RQ urate ra^ans of ..leosuring the b 'ginning and end 
 of the reactions is obtained. To show the diilic^lty produced by 
 
51 
 
 th i :}- responses of the colonies, -..he tira" taken for most 
 
 individuals to ^rosa the dish, i. e. ^' .;a.. , in white li.'ht bO om. 
 from the source in a straight line towards the aro was about 1 
 minute. ?n this distance was doubled, the time was still about 
 
 1 minute. When the c Iture was re::.cved 200 om. many c lonies still 
 requii-ed rrily 1 rainu^e to get icroes Uie dish. 
 
 This effect of Changing the distance was repeated with the 
 No. 70 filter, since as it transmits the longest wav~ lengths the 
 time cf the reaction nhculd be longer. However, they were still 
 too n.^.rt to obviate tho lar.je errors due to the indefinite end 
 points. At a distance cf 25 cm. Lhere was a noticeable collection 
 on tiie li ( shter si 3 of the dish. After 13 minutes nearly all had moved 
 over. At a distance nf 50 cm., ICO cm., :nc 200 cm., the same 
 positive reoulte v/ re c^ 'ith t>ie five minute exposure. Al- 
 
 though failing to si:ow the applicability of the Rosooe-Bunsen L w 
 this exp^riniont r^.cws th<; potency of the long red rays to oause the 
 same pro to tropisms produced by the blue waves when they aot with the 
 right intensity. 
 
 ~:ry exposure througiiouc, tli^-^e experiraents was made with a 
 fresh culture BC t.-at in no inst nee was tiiere a ch.ince of the 
 sensitiveness being ..ifior^nt for the succeaaive exposures because 
 of the of -fact I -ceedin t: ; illumination. 
 
 j (^9o3) reports that tiie positive p}:ototropism in 
 
 medium li'jht is reversed by strong light. Att-=>mpts w^ro made t): ere- 
 f re to find the turning point for each screen by .lessening its is- 
 tan*5e fro^i the aro. *t the control behind clear glass was the 
 
 only one in which any negative pho to t ro ;: i 3in could be obtained nnd the 
 response M -re varied at different times. In one experiment, the 
 
32-- 
 
 orgaii^ms reacted positively at 40 cm. from the aro, negatively at 
 20 cm. In another, the neutral point seamed to be 50 cm. away. 
 Quite often Tit this distance there were nearly as raany colonies 
 swimming away from as towards light. The response wis always more 
 definitely positive at 100 om. than at 50 era. Sometimes, however, 
 the response was mrstly positive as close as 10 om. , so that the re- 
 versal is dependent to a large extent en the -cndition of the org'-n- 
 isms as for the other screens, the greatest intensity obtainable be- 
 hind any was too low to produce any negative renuonse. 
 
 An entire carbon aro run was projected on one dish of 
 
 organisms. By looVing down it could be seen immediately that while 
 those crT.nir"3 fin din selves in the yellow, ^reen, blue and 
 
 violet lip;ht swam LowirdH the litf-.t, these of the red waved not to- 
 wards the front of the dish but in a direction por.^ii^i to it, i.e. 
 towards the yellow. The yellow apr.eared to the eye the Brightest 
 part of the dish. The organisms in it were dcubtless decidedly 
 photo vronic boc-'i-se of the relatively greater intensity, while those 
 of the blue were so in almost equal degree because cf the greater 
 ef f ectiveneflr* of these wave Tr-n;-:tr.8 even ^ t low intensity. In the 
 red the intensify wna not gre t en< ugh U) overcome the ineffectiveness 
 of the lon/3 r;iys, 30 tiie organisms responded either to an intensity 
 gradiant whi oh led them towards the yellow, or to > wave length 
 gradiant which would also lead tnen toward the yellow. Or the r - 
 suit might have be-=>n due to a diffusion of the more ei-:irint rays 
 into the red. The rara a red rayp in th< 5 naVed aro exposure thre 
 was no -iefl -ntion of the pat!"! leading dire^t-ly toward? the source of 
 light. 
 
--33-- 
 
 It is interesting in this connection to note Holt and Lee's 
 ) conclusions as to the vole of the intensity factor in phcto- 
 tropis . They ntate that, "T'n^re is no evidence t/iat 
 
 
 
 respond to any other property cf li^ht than its intensity. All 
 phototatio response in ^xplainea by the ii tensity of the 11,-^rt, and 
 the direction fro;a wai ^Ji it -lornes. 11 But my experiments 'Vith Volvox 
 show oonolu'9ively t/iac for Any Driven intensity the blu3 and violet 
 wave lengths tire --test stim luting effioienoy, but tliat by 
 
 increasin-; th-j duration of the exoosure the same effect is produced 
 
 L n d tlie otlir BCte^naJ and "by , aity of the 
 
 other colors they oan be made to produce an equally rapid re ponse. 
 This is in in or a i . 1 -.c-'t's ( '^'7 ) Conclusions that photo- 
 
 tropio resp'-na-jB are net entirely in ependent of intensity. 
 

 

 
 
 

 

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