PNIVERSITY OF CALIFORNIA PUBLICATIONS COLLEGE OE AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA PEAR POLLINATION BY WARREN P. TUFTS AND GUY L. PHILP BULLETIN No. 373 December, 1923 UNIVERSITY OF CALIFORNIA PRINTING OFFICE BERKELEY, CALIFORNIA 1923 Digitized by the Internet Archive in 2012 with funding from University of California, Davis Libraries http://www.archive.org/details/pearpollination373tuft PEAR POLLINATION By WAEREN P. TUFTS and GUY L. PHILP Whether the Bartlett and other leading varieties of pears require or are benefited by cross-pollination is a question which is arousing increasing interest on the part of pear growers, especially since the publication of a preliminary report on pear pollination. 1 This report being now out of print, it seems desirable to present at this time all the data available regarding the pollination requirements of the different pear varieties grown in California. The fact that Bartlett trees, planted without any regard to cross- pollination, have yielded profitable crops under valley conditions, has led some to believe that this variety is self -fertile. On the other hand, these same growers have noticed when they have a stray tree of some other variety in their orchard that the surrounding Bartletts are more fruitful than the remainder of the orchard. This seems to indicate that the Bartlett, under valley conditions, is benefited by cross- pollination. In the Sierra Nevada foothills, thoughtful and observant growers have felt sure that the Bartlett, under their conditions, is always self -sterile. With the increased plantings of pear varieties other than Bartlett under both valley and foothill conditions, the pollination question assumes a still greater importance. Waite 2 discovered about thirty years ago that the Kieffer pear, a leading variety of the eastern and middle states, is practically self- sterile. Since that time there has been much discussion throughout the country as to whether or not certain varieties other than the Kieffer could be benefited by cross-pollination and, if so, what varieties could be depended upon to serve as pollinators. Fletcher 3 states that: "The results of hand-pollinating 8408 Kieffer pear blossoms and 9867 Bartlett pear blossoms in the years 1903, 1906, and 1907 indicate: "1. In West Virginia and Michigan, and probably in other parts of the east, unsatisfactory results may be expected from planting either Bartlett or Kieffer in large blocks so that cross-pollination by insects is not general. i Tufts, W. P., Pollination of the Bartlett Pear, Calif. Agr. Exp. Sta. Bull. No. 307, May, 1919. 2 Waite, M. B., Pollination of Pear Flowers, Bull. 5, Div. Veg. Path., U.S. Dept. Agr., 1894. 3 Fletcher, S. W., Report of Va. Agr. Exp. Sta., 1909-1910. 4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION "2. Anjou, Lawrence, Duchess, and Kieffer are satisfactory varie- ties for planting with Bartlett, so far as pollination is concerned. Some years the Kieffer does not blossom simultaneously with Bartlett, but usually the blossoming seasons overlap sufficiently." Kraus 4 advises planting Clairgeau, Anjou, Howell, or Kieffer with Bartlett for the purpose of affecting cross-pollination. Wisker 5 says that: "California's pear profits would be greater if some other variety were planted with Bartlett for cross-pollination. Anjou, Bosc, and Cornice are good pollinators and sell for higher prices than Bartlett. We have increased the fruitfulness of an old Bartlett orchard more than 200 per cent by inter -grafting other varieties. ' ' Weldon believes that: "The best results in growing Bartlett pears cannot be attained unless other varieties are planted with them in the orchard. Despite the evidence that this should be done, there are thousands of acres of Bartletts being planted in California each season with utter disregard of the benefits that might be derived by planting one or more varieties for cross-pollination. In certain new pear-growing sections, the writers have recently seen thousands of acres of Bartletts in blocks of five acres to more than one hundred acres each, with no other varieties near, except possibly an occasional tree of some favorite pear planted for home use. "In some of these sections heavy winds and extremes of heat and cold occur, making more necessary the strictest attention to every detail that would tend to increase productivity. The fruit in general is good, and the trees everywhere have done well. So far as it has been possible to determine, they are self -fertile to a remarkable degree when the existing conditions are taken into consideration, but it is safe to predict that there will be years of short crops because of the absence of other pears, and the average production of these sections throughout a series of years will be far below what it would be with other varieties planted along with the Bartletts for cross-pollination purposes. There are older pear growing sections of the state where large areas of Bartletts have been planted by themselves and where the same arguments against the practice may be used." Although practically all writers agree in advising the inter-plant- ing of other varieties to pollinate the Bartlett, even in the valley locations in Cilifornia, nevertheless the bulk of the acreage planted i Kraus, E. J., The Pollination Question, Ore. Agr. Exp. Sta. Cire. Bull. No. 20, 1912. •> Wisker, A. L., Price List Loma Rica Nurseries, 1915-1916. (i Weldon, G. P., Pear Growing in California, Calif. State Com. of Hort., p. 234, 1918. Bulletin 373] PEAR POLLINATION 5 to Bartlett in the state contains no other variety. The authors of this paper outlined and performed certain experiments during the seasons of 1916, 1917, 1918, 1919, 1920, 1922, and 1923 designed to test the accuracy of the observations enumerated above. PKOBLEMS OF PEAK POLLINATION Inasmuch as the Bartlett is the pear of greatest commercial value in California, more attention in these experiments has been given to this variety than to others. The increasing interest of pear growers in varieties other than the Bartlett has resulted in the collection of some data with regard to the pollination requirements of certain of these sorts. In planning the work, of which this bulletin is a report the writers have had in mind the differ ences of altitude, climate, and soil, exist- ing in foothill, valley, and coastal regions in California, and have attempted to secure at least a partial solution of the following problems for these various conditions. 1. Will pears when planted in solid blocks be commercially profit- able without pollinizers? If found to be profitable under these con- ditions, these varieties may be termed self -fertile: if unprofitable, they should be termed self -sterile. 1 2. If pears will not, under all conditions, produce profitably in the absence of cross-pollination, what varieties should be used as pollinizers? This is a question of inter-fertility. 3. If it should be found that by inter-planting, the yield per tree can be increased, will the increase per acre make inter-planting com- mercially profitable? 4. Even though two varieties may pollinate each other, it is important that the following points should always be considered in selecting pollinizers : a. Commercial value of the pollinizer. b. Coincidence of bloom of the pollinizer with that of the variety to be pollinated. c. Succession of ripening of the varieties, for convenience in harvesting. d. Amount of pollen produced by the pollinizer. e. Germinability of the pollen produced by the pollinizer. 7 The writers prefer the terms "barren" and "fruitful" as explained by Kraus in the Journal of Heredity, vol. 6, no. 12. pp. 549-557, rather than the inexact terms, "sterile" and "fertile." The latter terms have been used in this paper on account of the fact that the general public is more or less familiar with these expressions. UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION Bulletin 373] PEAR POLLINATION OEGANIZATION OF THE WOKK The methods employed for investigating the problems just out- lined were those commonly in use in cross-pollination experiments. Briefly stated, this consisted of removing the stamens, the pollen- bearing organs, from the flowers to be pollinated (fig. 1) and then applying the desired kinds of pollen by hand. Accurate counts of the hand pollinated flowers were made and recorded. The fruits resulting from these artificial pollinations were counted and the proper records made after the June drop and again at harvest. Average Blossoming Pates or Certain Pear Varieties V//sivER5iTy Farm -Pavis, California- 614 TO I923~Lngl Le Go/ite Ale/scon Kiept-er No/cell fORELLE a^govle/ie Glairgeav Easter P.JiovEy PDARRy GlovtMorcEav Wl/HTER T^LIS BARTLETT BLOOPGOOP OAtlCE A/MJOV B.5.POX GlFEORP Comet Seckel hARpy Glapp Favorite COL.WlLPtR B05C y£AR5 averagep 9 8 9 9 MARCH APRIL i ■ m i r- mm 1 1 ■ ■ MiBi^-fifT-fl r PE5IGNAT E5 BEGIMLMG or- PULL Bloom Fig. 2. — The average dates of first, last, and full bloom of certain pear varieties covering a period of four to ten years. The number of years averaged is shown in a separate column. During the seasons of 1916, 1917, 1920, and 1923. experiments were conducted in the University Farm orchards at Davis, where typical Sacramento Valley conditions prevail. The trees are, at this writing, fourteen years old and are in an excellent state of vigor. In 1918 and 1919 experiments were conducted in the Vaca Valley Ranch orchards of the Earl Fruit Company at Vacaville. The trees are in full bear- ing, and are growing on some of the best soils in the valley. During the seasons of 1918, 1919, 1922, and 1923, certain experiments were conducted on the Loma Rica Ranch at Grass Valley. The trees in the Loma Rica orchards are nine years old and are making a moderate vegetative growth. This orchard is planted on typical red soil of the Sierra Nevada foothills at 3000 feet elevation. In 1920, experiments were conducted in the Santa Clara Valley, in the Keeble, Wilcox, and 8 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION McCurdy orchards. The trees in these latter orchards are in full bearing and in good condition. Several crosses were made in 1922 in the Searby orchard in the Occidental district of Sonoma County. Here the trees are healthy and in full bearing. THE BLOOMING PERIOD OF CERTAIN PEAR VARIETIES Figure 2 (p. 7) shows the average dates of the first, last, and full bloom of twenty-five pear varieties, as grown at the University Farm, Davis, for the years 1914 to 1923 inclusive (unless otherwise noted). Attention is called to the fact that the blooming period of the Bartlett is considerably longer than that of any other variety included in these studies. A careful study of these data as well as those presented b}^ Weldon, 8 including the blooming dates of nearly sixty varieties, leads to the conclusion that, with the possible excep- tion of a few very early blooming sorts such as the LeConte, Forelle, Kieffer, and Clairgeau, the blooming period of the Bartlett coincides very well with that of practically all other important varieties. Even the very early blooming varieties just mentioned do not, on the average, reach the height of their bloom many days before the Bartlett, and in most years their blooming periods overlap sufficiently to make them available as pollinators. PRODUCTIVENESS AND VIABILITY OF POLLEN USED In seven years' tests, there have been only three cases where pollen failed to give a satisfactory artificial germination. These were Blood- good and Seckel in the year 1920 and Surprise in 1923. In the case of Seckel, the self-pollinated flowers produced a three per cent set, indicating a partial germination under natural conditions. No reason can be given for the failure of the other two varieties of pollen to germinate artificially. Pear pollen, on the average, does not give as high germination tests as some of the other fruits, although a sufficient number of the pollen grains germinate to insure thorough pollination whenever the pollen is applied artificially. In selecting a pollinizer for his commercial orchard, the grower must take into consideration not only whether the pollen produced by a certain variety is viable, but also whether the variety selected is a good pollen producer. Fortunately all varieties tested have proved to be abundant pollen producers. Table 1 gives the average artificial germination of the different varieties used. s Weldon, G. P.. Pear Growing in California, Calif. State Com. of Hort., Bulletin 373] PEAR POLLINATION TABLE 1 Germinability of Pollen Percentage germination in a 12 per cent cane sugar solution Seasons 1916 to 1923 ; inclusive Variety Source 1916 1917 1918 1919 1920 1922 1923 Alencon Univ. Farm 63 26 9 33 22 45 26 63 21 41 36 32 76 42 19 74 43 58 39 25 45 36 44 8 26 16 22 24 21 35 29 15 6 23 25 6 29 20.3 12 22 41 80 75 62 62 22 82 54 46 36 58 40 44 45 21 17 30 17 33 17 55 38 18 28 11 36 21 35 10 40 20 73 58 80 30 18 5 15 82 85 15 44 18 18 8 37 10 31 31 20 45 18 19 42 58 13 15 19 63 27 38 70 36 15 17 33.6 Anjou Univ. Farm Anjou . .. Grass Valley Angouleme Univ. Farm Bartlett Univ. Farm 62 Bartlett. Grass Valley 31 Bartlett Vaca Valley Bartlett Sonoma Co... . Bartlett Santa Clara (Mc) .... Univ. Farm Bloodgood Bloodgood Santa Clara (W) Univ. Farm Bosc Bosc Grass Valley 21 Clairgeau Univ. Farm 69 Clairgeau Grass Valley Clairgeau Santa Clara (K) Univ. Farm Clapp Favorite.. .. 88 Col. Wilder Univ. Farm 35 Cornice Univ. Farm 73 Cornice Grass Valley 13 Cornice Santa Clara (K) Univ. Farm Dana Hovey 88 Dana Hovev Grass Valley Easter Univ. Farm 52 Easter Grass Valley Easter Santa Clara (Mc) .... Univ. Farm Flemish Beauty.... Forelle Univ. Farm 90 Forelle.... Grass Valley Gifford Univ. Farm G. Morceau Univ. Farm G. Morceau Santa Clara (Mc) .... Univ. Farm Hardy Hardy Santa Clara (K) Univ. Farm Howell Howell Grass Valley Howell Santa Clara (S) Univ. Farm Kieffer Le Conte.... Univ. Farm Lincoln ... Grass Valley Madeline Univ. Farm Patrick Barry Patrick Barry Seckel Univ. Farm 91 Grass Valley Univ. Farm 87 Seckel Grass Valley Surprise Univ. Farm W. Bartlett .. . Grass Valley W. Nelis.. . Univ. Farm 44 W. Nelis . Grass Valley 11 W. Nelis Santa Clara (Mc) .... Santa Clara (Mc) .... Average W. Seckel 57 Mc, McCurdy orchard; K, Keeble orchard; W, Wilcox orchard; S, Smith orchard — all in the Santa Clara Valley. 10 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION RELATION OF NORMAL SET TO FINAL CROP Immediately after the petals fall, each flower begins to form a fruit. During the following two or three weeks a certain percentage of these young fruits, for reasons not fully understood, drop off, leaving only a rather low percentage of the total number of original blossoms to continue development. It is quite necessary that this drop take place, as the tree under average circumstances would never be able to carry so many fruits through to maturity. Just what factors determine which of these young fruit shall drop is not at present known. Later in the season there takes place still another falling of the young fruits known as the "June drop." The expression normal set is a more or less technical way of designating the percentage of fruit which the tree sets under normal conditions when left open to insect pollination. It is obvious that the normal set may be determined at any time up to the end of the season by counting the fruits on a tree and comparing the number with the original bloom. In these experiments, approximately 2000 blossoms of each variety, well distributed over the trees, were counted each year and proper records kept to determine the normal set after the first drop, after the second drop, and at harvest time. The questions at once arise as to what percentage of normal set at harvest time constitutes a full crop, and what is meant by a "full crop." What constitutes a full crop of any fruit is perhaps largely a question of opinion, judgment, or guess. It varies with such factors as variety, soil, and moisture conditions. What would be considered a full crop under foothill conditions would not necessarily be the same in a valley location. Table 2 casts some light upon the question as it shows the normal set of the Anjou, Hardy, Clairgeau, Flemish Beauty, and Forelle in 1922, as grown under conditions existing in the University Farm orchards. The average yield of these trees has been reduced to an acreage basis. The trees under observation were planted during the spring of 1912, being twenty-four feet apart by the square system, which gives approximately seventy-five trees to the acre. Since plant- ing, these trees have received good commercial care. All figures are based on pears harvested. An examination of the figures presented in table 2 shows that too much emphasis must not be placed on mere percentages. It will be noted that the normal set for Hardy was only 3.5 per cent with a yield of 12,550 pounds of fruit, while Flemish Beauty on the other hand, had a normal set of 18.2 per cent with practically the same Bulletin 373] PEAR POLLINATION 11 yield. Forelle, with a normal sot of 25.2 per cent, produced 31,875 pounds of fruit. These variations in yields are explained by the heavier bloom of those varieties maturing a heavy crop with only a small percentage of the blossoms setting. These figures are presented to show the necessity of taking the " normal set" counts every year on the different varieties in order to secure a correct basis for judging results of artificial pollination. TABLE 2 Comparison of Normal Set with Yield in Pounds per Acre University Farm, Davis, 1922 Variety Per cent Pounds per acre Anjou Clairgeau Hardy Flemish Beauty Forelle 12,851 21,600 12,550 12,075 31,875 POLLINATION KEQUIEEMENTS OF THE BAETLETT PEAE A. Interior Valley Conditions During the seasons 1916, 1917, 1920, 1922, and 1923, experiments were conducted in the University Farm orchards at Davis for the purpose of determining whether the Bartlett would set fruit with its own pollen under Sacramento Valley conditions. At the same time numerous crosses were made on the Bartlett to find the best pollenizers for that variety (fig. 3). The results of this work are summarized in table 3. In solidly planted Bartlett orchards, it has been observed that in years of heavy bloom a two or three per cent set from the self- pollinated flowers may give a satisfactory yield- However, in the long run, experience teaches that there is likely to be many years of light crops, if only the one variety is planted. It will be noted from a study of table 3 that self -pollinated flowers gave a distinctly lower set than did those crossed with pollen of other varieties except in the case of Howell in 1917 and Anjou in 1922. During all years the Bartlett showed evidence of self -sterility. Of the varieties used as pollinizers for the Bartlett, Winter Nelis has always given the highest set of fruit. The writers feel that under average conditions and over a long period of time this variety should be given 12 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION pq * 111 © 00 rH CO O Oi GO o rH CO •O rh CO Numl of bios som use< GO rH N 00 ^ rH 00 H/l GO CM TjH CM tO CM i-i l> CO to l|l rH O H^ THH o o t- rH CO 1> CO O rH CM Oi u _Q ' oq_-i 00 CM Oi to CO tH uml of bios som usee O 00 tO Tti O CO Oi CO "* "* CO CO % J5ll ^ H T)H o O 00 00 t^ CO ^ CO H © TH «H © CO Oi CO CO Oi Oi ° rH rH CM rH rH rH rH (h rH Numbe of blos- soms used CO ■* H Oi O 1>- GO rH GO "* to CO 00 iO 00 N CM O CM rH Oi CO ^ CO CM tF CO t* CM CO CO « fl aJ Ah § « : b- co : Oi co rH 00 <* CO Oi CO 00 o> CM CM rH (M 1* umbe of blos- soms used CD tH 00 GO 00 CD b- CM t^ O CO to o> H rH ■^ i §T3 t^ CO O rH Oi tO u 1—1 % fh 2t3 CD tQ CO 00 3 43§3 rH O I> o rH CM co £ -u * 1 m .* +J 'a; CO 525 Hi M P r O c t+_ «4_i DC .n EC a z: ster. relle. rdy. well, nter fe 'S ^ "S -3 o o ^ d o °5 O ir 1 Z V X X X X x x X X X X x l 23 g g 53 E -g Is II « S S=5 .- CO "8 •*^ 03 ►» c3 O -3 ■^ .2 -2 D S « rH PQ PQ Bulletin 373] PEAR POLLINATION 13 preference as a pollinizer for the Bartlett. Cornice, Bosc, Easter, and Hardy also have given satisfactory results and are recommended in the order named. Howell, Angouleme, Anjou, and Forelle have likewise been fairly satisfactory as pollinizers. BARTLETT PEAR POLLITNATIO/iS Interior Valley Locatjons~Vaca\6lley l3l8.l9l9~\yni\A3rsitu.0rchards,l^isl9l6,l9IZ I32I.I92Z.I923. Gross Formal Set xSelt- xA/IGOVLEME xA/sjov xBosc xGoMICE. xEaster xHarpy xHoVYELL xWLnTER /1EU5 Percent ot Blossoms Maturing 1916 1919 \3Z\ I92Z ■ 1 1 1 ■ I ■ 1 ■ ■ ■ Fig. 3. — This chart shows the influence of various kinds of pollen when applied to the flowers of the Bartlett pear under interior valley conditions. Note the comparatively light set of fruit when the Bartlett flowers were self- pollinated. B. Coastal Conditions The work under coastal conditions was done in 1920 in the Santa Clara Valley and in 1922 in Sonoma County. The results of this work are presented in table 4. A study of table 4 shows some rather interesting results. In Santa Clara Valley, the Wilcox and Mc Curdy orchards exhibited a wide difference both in the normal set and self-pollination tests. In the former orchard, the Bartlett was practically self-sterile, while in the latter it was self -fertile. Also, the normal set in the Wilcox orchard was less than half that in the McCurdy orchard. Both of the orchards ar? considered good producers. Possibly the differences in soil can- ditions and cultural treatments may be responsible for the seemingly conflicting results given above. Cornice and Winter Nelis proved to be the best pollinizers for the Bartlett, while Clairgeau and Easter gave only fair results; Glout Morceau and Howell proved to be practically inter- sterile with the 14 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Bartlett. Since facilities have not been available for repeating these experiments, definite conclusions cannot be drawn at this time. In Sonoma County, the only work attempted was self -pollinating the Bartlett and crossing that variety with the Winter Nelis. Weather conditions were not favorable for the setting of fruit in this section in 1922, but while the percentage set was small the crop was fairly satisfactory. It should be noted that while the Bartlett was to a certain degree self-fertile, the set was materially increased by using Winter Nelis as a pollinizer. TABLE 4 Bartlett Pear Pollination under Coastal Conditions 1920 1922 Bartlett Number of blossoms counted Per cent set Number of blossoms counted Per cent set Normal Set 1980 Mc 3718 W 506 Mc 549 W 493 W 524 W 500 W 504 W 484 W 548 W 20.0 9.8 12.4 0.5 4.8 24.2 4.4 0.4 0.6 23.5 2013 S 472 S 451 S 1 2 Normal Set xSelf 2 5 xSelf xClairgeau xComice xEaster xGlout Morceau xHowell xWinter Nelis 5.3 Note: — 1920. Work done in Santa Clara County. Mc, McCurdy orchard; W. Wilcox orchard. 1922. Work done in the Searby orchard, Sonoma County. C. Sierra Nevada Foothill Conditions Pollination experiments were conducted in the Sierra Nevada foothills during the seasons 1918, 1919, 1922, and 1923. The results of this work are presented in table 5. It is the general opinion of pear growers that under Sierra Nevada foothill conditions, Bartlett pears must be cross-pollinated to produce satisfactory crops. A study of table 5 indicates this to be the case. During three of the four years that these experiments were in progress, the Bartlett was largely self-sterile, this self-sterility occurring entirely too often to justify an orchardist in attempting to grow pears without providing for cross-pollination (fig. 4). The "Winter Nelis has proved to be the best pollinizer for the Bartlett. Although all the other varieties tested proved to be satis- Bulletin 373] PEAR POLLINATION 15 factory pollinizers, preference should possibly be given to Winter Nelis, Bosc, Cornice, and Anjou in the order named. Table 6 presents the results of an experiment designed to show, from the average yield of two comparable orchards, the benefits to be derived from cross-pollination. The orchard of P. M. Beaser of TABLE 5 Bartlett Pear Pollination in Sierra Nevada Foothills 1918 1919 1922 1923 Number blossoms counted Per cent set Number blossoms counted Per cent set Number blossoms counted Per cent set Number blossoms counted Per cent set Bartlett Normal Set.. xSelf 2916 918 518 426 459 414 19.5 1.3* 18.7 20.6 15.4 20.1 2583 398 377 396 310 407 3.8 16.0 18.8 27.2 19.3 21.8 1732 634 517 500 532 429 496 530 452 2.7 0.1 1.9 1.8 4.8 2.3 3.0 3.9 5.1 3026 926 612 546 893 7.2 0.0 xAnjou xBosc xComice xEaster xHovey xHowell xW. Nelis .... 11.0 13.0 14.0 ♦Fruit small. BARTLETT PEAR POLLI/i AT 10/15 5ierra Nevada Poothifl Locations ~- Grass Valley 1918 - 1919 ~ 192 2 "1923 Gross Percent of Blossoms Maturing 1318 1319 19ZZ. 1923 /Formal 5e.t x5ele xA/ijov; xBosc xComice xEaster xhovEy xHi/iter /SELI5 ■■■__■ I B HH _ BKBI I ■■___ ■ ■■_ SB I ■■■___■■■■_■ ■BH I L ■»_ Fig. 4. — This chart shows the influence of various kinds of pollen when applied to the flowers of the Bartlett pear under Sierra Nevada Foothill locations. Note the failure of the trees to set fruit when self -pollinated. 16 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Chicago Park, Nevada County, consists of a solid block of one thousand Bartlett pear trees, no provision having been made for cross-polli- nation. These trees are perhaps twenty-five years old. There is located on the Loma Rica Ranch, some eight miles away, a small block of old Bartlett trees of about the same age and vigor as those on the Beaser place. Many of these trees had, however, during the six or eight years previous to 1918, been topworked to other varieties. AVith the exception of the presence of pollinating varieties close at hand on the Loma Rica Ranch, the two orchards just described were in all respects comparable. Both orchards bloomed profusely in 1918. TABLE 6 Comparison of Yield on Bartlett Trees in Nevada County with and without Pollinating Varieties, 1918. With Pollinating Varieties Without Pollinating Varieties Number blossoms counted Per cent set Average yield per tree in packed boxes Number blossoms counted Per cent set Average yield per tree in packed boxes 3007 14.9 2.19 3170 6.0 .77 The figures show that the trees provided with cross-pollination produced a crop almost three times as great as that produced by the trees which did not receive cross-pollination. It should also be noted that the favorable showing for the trees receiving cross-pollination was made in spite of the fact that this orchard lost much of its fruit as a result of the ravages of pear blight. POLLINATION EEQUIEEMENTS OF CEETAIN PEAE YAEIETIES OTHEE THAN THE BAETLETT A. Interior Valley Conditions Some twenty-five pear varieties have been tested as to their pollination requirements when grown under interior valley conditions. These experiments were conducted in the University Farm orchards at Davis. The major portion of this work consisted of the determi- nation of normal sets and the testing of the varieties for self -sterility or self-fertility. A few cross-pollinations were made between some of the varieties. Tests have been conducted for from one to four years. The results of this work are presented in table 7. Bulletin 373] PEAR POLLINATION 17 TABLE 7 Pollination of Pear Varieties Other than Bartlett University Farm, Davis, 1919, 1920, 1922, 1923 1919 1920 1922 1923 Variety Number counted Per cent set Number counted Per cent set Number counted Per cent set Number counted Per cent set Alencon Normal Set 249 79 254 227 172 193 512 451 499 433 17.3 6.1 26.1 0.0 23.8 2.1 15.4 13.1 15.2 5.3 990 511 881 293 724 335 843 576 246 265 839 307 530 288 736 300 498 302 727 811 122 168 0.0 0.0 0.1 0.0 7.0 0.6 7.7 0.3 12.0 0.1 5.9 0.0 14.0 0.6 7.4 0.0 0.9 0.0 7.0 6.0 2.4 0.0 314 559 240 483 183 710 306 427 757 432 214 340 161 884 581 1.2 0.0 10.0 6.4 7.1 20.4 13.4 0.0 5.5 0.0 0.0 2.3 1.2 3.9 0.3 900 272 179 1313 374 232 358 1326 342 1643 548 1549 260 1759 392 xSelf Angouleme Normal Set xSelf Anjou Normal Set xSelf Bloodgood Normal Set xSelf Bosc Normal Set 48.6 xSelf xComice 63.2 xEaster 29.6 B. S. Fox Normal Set xSelf Clairgeau Normal Set 15.7 xSelf 7.3 xComice 14.5 xW. Nelis Clapp Favorite Normal Set 10.6 8.7 xSelf 2.6 Col. Wilder Normal Set 20.3 xSelf 6.0 Comet Normal Set xSelf Cornice Normal Set 19.9 xSelf 6.5 D. Hovey Normal Set 19.5 xSelf 11.7 18 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION TABLE 7— (Continued) Variety 1919 Number counted Per cent set 1920 Number counted Per cent set 1922 Number counted Per cent set 1923 Number counted Per cent set Easter Normal Set xSelf Flemish Beauty Normal Set xSelf Forelle Normal Set Self Gifford Normal Set xSelf Glout Morceau Normal Set xSelf Hardy- Normal Set xSelf xComice xEaster Howell Normal Set xSelf Kieffer Normal Set xSelf >, LeConte Normal Set xSelf P. Barry Normal Set xSelf Madeline Normal Set xSelf Seckel Normal Set xSelf Winter Nelis Normal Set xSelf xSelf G.V.f Cornice * Per cent set estimated 403 317 442 957 463 385 165 900 209 57 195 1048 442 8.7 13.6 9.3 6.8 3.5 4.9 5.5 7.5 0.0 63.2 4.6 12.4 0.0 799 275 608 315 501 274 538 307 701 227 673 277 640 278 457 557 938 311 516 307 804 238 341 4.0 0.7 10.0 0.0 14.0 0.0 3.9 0.6 8.5 7.5 0.6 0.3 8.2 0.0 14.0 0.0 7.9 0.9 22.0 3.0 6.0 0.0 0.0 376 356 142 226 258 472 710 117 239 276 752 530 64 407 441 551 1528 329 301 474 1003 151 579 4.0 0.8 18.2 6.2 25.2 0.0 10.3 2.7 3.4 2.1 3.5 0.3 2.0 4.4 14.9 0.2 3.6 0.0 8.3 0.8 8.1 0.0 15.0 s 0.0 1601 317 1555 441 381 1414 267 1628 319 533 423 108 1464 764 3.7 6.3 3.8 4.7 14.7 7.1 0.0 11.5 2.8 77.5 19.8 6.7 0.2 16.5 t Pollen from Grass Valley. Bulletin 373] PEAR POLLINATION 19 In order to summarize the results presented in table 7, the writers have segregated the varieties into three groups as follows : Self-Sterile Self-Fertile Doubtful Variety Years tested Variety Years tested Variety Number years self- fertile Number years self- sterile Alencon 2 2 1 1 2 3 1 3 Cornice 4 1 3 3 Angouleme 1 2 1 1 2 2 1 1 1 1 1 3 1 Bloodgood 1 B. S. Fox Flemish Beauty.. Hardy Howell Anjou 1 Comet Bosc 1 Forelle Clapp Favorite . . Clairgeau 1 Le Conte 2 Madeline.... Col. Wilder 2 Winter Nelis Dana Hovey Easter Gifford G. Morceau Kieffer 2 2 1 1 4 P. Barry 2 Seckel 1 Those varieties listed as self -sterile must be provided with some other variety to pollinate them. While the self -fertile varieties may be expected to produce good crops without pollinizers, it should be noted from the table that in no case did the self-pollinations equal the normal set. The advantage of cross-pollination is thus clearly shown since these trees are located in a variety orchard, where abundant opportunity for cross-polli- nation is afforded. The doubtful varieties are those which have not behaved con- sistently from year to year. For instance, the Anjou was self -fertile in 1919 and 1922, but largely self -sterile in 1920, and the Clairgeau was self -fertile two years and practically self -sterile two years. It would be inadvisable to plant these doubtful varieties in solid blocks, as there would be too many years when they would be self -sterile or practically so, and would not produce paying crops. Only a few cross- pollinations have been made with these varieties but in each case a very satisfactory set has been obtained. 20 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION B. Coastal Conditions Experiments under coastal conditions have been rather limited, consisting of one year 's trial in the Santa Clara Valley and work with one variety in Sonoma County. The results of this work are presented in table 8. TABLE g Pollination of Pear Varieties Other than Bartlett Coastal Conditions 1920 1922 Variety Number of blossoms counted Number set Per cent set Number of blossoms counted Number set Per cent set Bosc Normal Set , xSelf 1987 410 1901 422 205 1758 425 327 304 2000 486 2000 892 353 40 2108 404 299 308 1237 531 1025 532 2000 486 342 315 231 527 82 92 3 71 4 2 91 99 55 123 75 54 6 73 5 81 110 15 32 8 218 7 59 52 19 26 20 4.8 0.0 1.4 4.0 0.9 0.6 29.9 4.4 11.3 6.1 8.4 15.0 12.0 3.4 1.2 27.0 35.7 1.2 0.0 3.1 1.5 10.0 1.4 17.0 16.0 8.0 1793 485 220 81 1 31 Clairgeau Normal Set xSelf xForelle Cornice Normal Set xSelf xHowell xW. Nelis Easter Normal Set xSelf Glout Morceau Normal Set xSelf xEaster xW. Nelis Hardy Normal Set xSelf xComice xW. Nelis Howell Normal Set xSelf Winter Seckel Normal Set xSelf Winter Nelis Normal Set.. 4.5 xSelf 0.2 xBartlett 14.0 xEaster xGlout Morceau Bulletin 373] PEAR pollination 21 From the preceding table it will be noted that Clairgeau, Cornice, Howell, Hardy, and Winter Nelis proved to be self -sterile or prac- tically so. Bosc, Easter, and Glout Morceau are self-fertile. Although Winter Seckel produced considerable fruits when self- pollinated, it has been classified as partially self -sterile. Since the set from self-pollinations was low when compared with the normal set, the writers believe that this variety should not be planted in solid blocks. C. Sierra Nevada Foothill Conditions Experiments were conducted under foothill conditions during the years 1919, 1922, and 1923. The results of this work are presented in table 9. A study of table 9 shows Anjou, Cornice, D. Hovey, and P. Barry to be self -sterile or practically so. Bosc may be classed as doubtful since it was sterile one year and partially self-sterile the other. The one season's results indicate that Easter is self -fertile. It is interesting to note that in all cases the Bartlett has proved to be a satisfactory pollenizer. With the exception of Winter Nelis X Bosc and the reciprocal cross, pollinations with Bartlett have given the highest yields. With the exception of Dana Hovey X Bartlett, all crosses made have increased the set over that obtained by the normal count, and in most cases the resultant set was two or three times as much as that produced under field conditions. Reimer 9 observes in southern Oregon that the Bartlett is not a good pollinizer for Anjou and also that a satisfactory pollinizer for the Cornice is yet to be found. The writers feel that the conflict between Oregon observations and the results obtained in California are perhaps due to climatic factors. From the preceding discussion it seems reasonable to draw the following conclusions : Under Sierra Nevada foothill conditions all pear varieties should be considered as self-sterile — meaning that it is inadvisable to plant pears without provisions for cross-pollination. The Bartlett can be considered as a satisfactory pollinizer for other varieties. INFLUENCE OF CROSS POLLINATION UPON THE JUNE DROP Table 10 gives in detail the results of certain experiments con- ducted in the orchards of the Vaca Valley Ranch of the Earl Fruit Company at Vacaville during the season of 1918 (figs. 5 to 10, inclusive). This orchard consists of a solid block of Bartletts, no provision having been made for cross-pollination. » Reimer, F. C, Better Fruit, vol. XVIII, Nov. 6, 1923. 22 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION TABLE 9 Pollination of Pear Varieties Other than Baetlett Sierra Nevada Foothill Conditions 1919 1922 1923 Variety Number of blos- soms counted Number set Per cent set Number of blos- soms counted Number set Per cent set Number of blos- soms counted Number set Per cent set Anjou Normal Set... xSelf 1747 311 218 300 1258 148 120 1048 274 226 1713 376 330 1559 387 352 51 32 28 156 3 55 9 15 11 5 37 53 2 11 2.8 0.0 14.6 9.3 12.4 0.0 2.5 5.2 3.0 6.6 0.6 1.3 11.2 3.3 0.5 3.1 2170 476 386 364 2062 521 474 341 2188 770 495 477 551 566 2391 370 477 442 340 408 89 27 21 94 11 22 27 10 20 10 29 22 48 42 23 38 4.1 0.0 7.0 5.7 4.5 2.1 4.6 7.9 0.0 0.0 2.0 4.2 1.8 0.0 1.2 5.9 10.0 9.2 6.7 9.3 1398 527 392 290 2958 1110 552 479 629 2537 551 534 534 465 56 35 27 110 6 51 42 75 259 1 85 146 54 xBartlett xBosc xHowell Bosc Normal Set.... xSelf 4.0 0.0 xBartlett xW. Nelis Cornice Normal Set.... [xSelf 8.5 9.3 3.7 0.5 xAnjou xBartlett xBosc 9.2 8.9 xW. Nelis D. Hovey Normal Set.... xSelf xBartlett Easter Normal Set.... xSelf 11.9 xBartlett P. Barry Normal Set.... xSelf xBartlett Winter Nelis Normal Set.... xSelf 10.0 0.0 xAnjou xBartlett xBosc 15.9 27.3 xComice 11.6 xEaster Bulletin 373] PEAR POLLINATION 23 Fig. 5. — A typical example of the normal set in the Vaea Valley Eanch orchards, 1918. Two pears matured from seventeen blossoms — a 11.7 per cent set. In years of normal bloom a 10 per cent set would assure a satisfactory crop. 24 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Fig. 6. — Two Bartlett pears set from eight blossoms pollinated with Bartlett pollen. A typical cluster of this variety when self -pollinated. Vaca Valley Ranch, 1918. Bulletin 373" PEAK POLLINATION 25 Fig. 7. — Five Bartlett pears set from twelve blossoms pollinated with Cornice pollen. A typical cluster resulting from crossing Bartlett with Cornice. Vaca Valley Ranch, 1918. 26 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Fig. 8. — Four Bartlett pears set from seventeen blossoms pollinated with Easter pollen. A typical cluster resulting from crossing Bartlett with Easter. Vaca Valley Ranch, 1918. Bulletin 373] PEAR POLLINATION 27 Fig. 9. — Eleven Bartlett pears set from twenty-five blossoms pollinated with Howell pollen. A typical cluster resulting from crossing Bartlett with Howell. Vaca Valley Ranch, 1918. 28 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Fig. 10. — Ten Bartlett pears set from twenty blossoms pollinated with Winter Nelis pollen. A typical cluster resulting from crossing Bartlett with Winter ^elis. Yaca Valley Ranch, 1918. Bulletin 373 PEAR POLLINATION 29 Fig. 11. — Bartlett pears (left), self-pollinated (right), cross-pollinated with Winter Nelis. Showing the characteristic shape of each and. the relative amount of core tissue. 30 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION It is unfortunate that the normal set count of the fruits matured could not be secured. The branches on which these records were made received the customary hand thinning early in the summer and therefore later counts would not have been reliable. TABLE 10 Pollination of the Bartlett, 1918 Vaca Valley Eanch, Vacaville Variety Number of blossoms counted Number set Per cent apparently set May 10 Number fruits matured Per cent matured Bartlett Normal Set 1276 424 278 308 238 256 108 79 90 86 63 75 8.4 18.6 32.3 27.9 26.4 29.2 41 73 71 47 60 xSelf 9.7 xComice xEaster 26.3 23.1 xHowell 19.8 xWinter Nelis 23.4 Those flowers which were self -pollinated matured a much smaller crop than did those which were crossed with pollen from other varieties. It is interesting to note from the above table that the loss from the June drop of those fruits resulting from cross-pollination amounted to only 20 per cent, while with those self -pollinated the loss was 48 per cent. This would seem to indicate that fewer pears will be lost at the June drop if adequate provision is made for cross- pollination. Inasmuch as the resulting set in this orchard when the blossoms actually received their own pollen was more than double the normal set, it seems clear that the provision of some agency, preferably honey bees, for the transfer of pollen from flower to flower would be highly profitable. INFLUENCE OF CROSS POLLINATION UPON MATURITY, SHAPE, QUALITY, PRODUCTION AND KEEPING PERIOD Blanchard 10 observes that: "In the Antelope Valley Bartlett pears resulting from cross-pollinated flowers mature their fruit from two to three weeks earlier than those fruits resulting from self-pollination. There is also a marked increase in the yields from orchards having pollinating varieties present. ' ' 10 Blanchard, V. F., Unpublished data, Los Angeles County, 1923. Bulletin 373] PEAR pollination 31 Overholser and Latimer 11 report that: ''The flavor of cross- pollinated pears from the Antelope Valley was richer, but had only about three-fourths as much edible flesh as the self -pollinated fruit, because of the amount of tissue comprising the core of the former. The characteristic shape of the self -pollinated Bartlett pear is different from the cross-pollinated pear (fig. 11). There was little apparent difference in the length of the keeping period between the self- pollinated and cross-pollinated Bartlett and Winter Nelis." The writers do not know of any other section where the self- pollinated Bartlett behaves as it does in the Antelope Valley, but certainly under those conditions it is highly desirable to provide for cross-pollination. Another variety where cross-pollination is highly desirable is in the case of the Glout Morceau, which generally produces irregular shaped fruits when self-pollinated. EECOMMENDATIONS From a study of the experimental data presented and from the observations and experiments of many orchardists of the state, the conclusion is inevitable that pear orchards should in general be provided with facilities for cross-pollination. Since the Bartlett is the most important variety grown in the state at the present time, the question at once arises as to what variety shall be selected as a pollinizer for it. For foothill locations where the bulk of the crop is offered for "green" shipment, this question is probably not difficult to answer. Tn these places, the Anjou, Bosc, Cornice, Howell, and Winter Nelis are all excellent pears, bringing prices equal to or better than the Bartlett for eastern shipment. These varieties may not give an equal tonnage with the Bartlett, but they are all fair producers. The Cornice should be avoided in windy locations, since its skin is quite delicate and mars most easily. In valley locations the question of providing cross-pollination for the Bartlett is more difficult. The grower must concede that where the set can be increased 100 per cent or more by the planting of one pollinating tree to every eight Bartletts, the returns per acre will still be greatly increased even though the fruit of the pollinating variety may have little or no commercial value. Although there has been no thorough attempt to test the adaptability of various varieties to different locations, the writers believe from the information in hand ii Overholser, E. L., and Latimer, L. P., Calif. Agr. Exp. Sta. Ann. Kept., p. 130, 1922. 32 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION that the Winter Nelis will prove, from all standpoints, to be the most efficient pollinizer for the Bartlett when grown under valley con- ditions. Cornice, Bosc, Easter, and Hardy also have given satisfactory results and are recommended in the order named. Where dried fruit is a primary product and where the fruit of the pollinizer for the Bartlett must also be dried, special difficulties are presented. No experiments have as yet been conducted in this state to determine the drying qualities of the various varieties. In order to avoid the use of artificial evaporators, the pollinizer must ripen its fruit at about the same time or shortly after the Bartlett. Practi- cally all dried pears in California are sundried. Keeping especially in mind the time of ripening, the Howell and Hardy varieties seem to be the best pollinizers for the Bartlett where the entire crop is to be dried. Under coastal conditions Winter Nelis and Cornice should prove to be the most efficient pollenizers for the Bartlett. Although comparatively few cross-pollinations have been made on varieties other than the Bartlett, the writers feel from the data pre- sented that the Bartlett may be successfully used as a general pollinizer. This is especially true of the more important sorts, such as Anjou, Bosc, Cornice, Hardy, Howell, Easter, and Winter Nelis. POLLINATING AGENCIES After planting inter-fertile varieties, the orchardist should by all means provide an agency for the transfer of the pollen from the trees of one variety to those of another. The common honey bee is by far the best carrier of pollen: it will pay the grower to keep bees even though he may not care to go into the honey business. Bees, however, are a very profitable side line for the orchardist, especially if alfalfa fields are available to work on after the blooming season of fruit has passed. About one hive of bees to an acre of bearing orchard should be provided. Preferably the hives should be scattered as widely as possible throughout the orchard during the blooming season. Experi- ments and experience have shown that little reliance can be placed on wind and insects, other than the honey bee, in effecting the transfer of pollen from tree to tree or, in fact, from flower to flower. Gossard and Walton 12 show that under Ohio conditions, pear blossoms which have been pollinated for 72 hours are not likely to 12 Gossard, H. A., and Walton, R. C, Dissemination of Fire Blight, Ohio Agr. Exp. Sta. Bull. 357, 1922. Bulletin 373] PEAR pollination 33 be inoculated with pear blight and that susceptibility to the disease does not exist in blossoms that have been pollinated for 144 hours. These writers infer that the presence of numerous honey bees in an orchard at blossoming time will insure a good crop of fruit by bringing about the pollination of each flower as soon as it unfolds, thus rendering a majority of the bloom non-susceptible to blight before the disease is generally diffused over the orchard. The relation of bees to the spread of pear blight under California conditions is a question which requires additional investigation. The work in Ohio would seem to indicate that numerous bees in the orchard early in the season would be an advantage in restricting the ' ' blossom blight, ' ' in addition to their necessity as pollinating agents. Eliminating from consideration all conditions which may influence the fruitfulness of an orchard except those occurring at the blossom period, it may be said that the set is largely influenced by weather conditions at that time. Cold weather, aside from killing the blossoms or lowering the vitality of the pollen, often prevents bees from work- ing. The same is true if cloudy, wet. and windy weather prevails. For their best work bees demand clear, warm, and quiet days, and since the weather at the time of bloom is often quite unsettled, it is readily seen that the blossoming period of the various pollinating varieties should overlap perhaps a week in order that there may be one or two days at least when the weather will be favorable for insect pollination. ARRANGEMENT OF THE ORCHARD FROM A POLLINATION STANDPOINT In planting an orchard it is desirable to have at least every sixth and preferably every fourth row of a pollinating variety. For con- venience in the management of the orchard, it is best to plant two rows of one kind, then two rows of the pollinating variety, and so on ; or, if it is desired to have more of one varietj^ than another, four rows of the favorite variety, then two rows of the pollinizer, and repeat. For one reason or another, it is often desirable to reduce the number of pollinating trees to the minimum. Under these circumstances, one tree in twenty-five is perhaps sufficient, although at least one tree in eight is strongly recommended. It is seldom wise to graft over a part of a tree to the pollinating variety as this tends toward confusion and added expense in harvesting. 34 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION In planting one tree of the pollinizer to seven or eight of the main variety, the former should be placed as every third tree in every third row in such a way that the spaces in the pollinating rows are broken as indicated in the diagram, the ' * r ' in each case representing a pollinating tree. . . If by chance a self -sterile variety has been planted in a solid block, the necessary pollinizer may be introduced by grafting. Some relief may be obtained during the years while waiting for the trees grafted over to pollinating varieties to come into bearing, by cutting off large limbs of pollinating varieties, placing the cut ends in buckets of water and distributing them throughout the orchard during the blooming period. Such limbs will live for several days and continue to bloom, forming pollen for the bees to transfer to the self -sterile variety. SUMMARY OF PEAR POLLINATION 1. A 12 per cent cane sugar solution gave during the seasons of 1916, 1917, 1918, 1919, 1920, 1922, and 1923, an entirely satisfactory artificial germination of pear pollen. 2. There is comparatively little variation in the amount of pollen produced by various pear varieties. Pollen production is always abundant. 3. The blooming period of most pears is comparatively short. 4. With the exception of several of the earliest and latest bloomers all pear varieties overlap in their period of bloom. 5. Bartlett is to a limited extent self -sterile under interior valley and coastal conditions. Under Sierra Nevada foothill conditions it is almost entirely self -sterile (at least in certain years) and therefore should not be planted without pollinizers. Bulletin 373] PEAR POLLINATION 35 6. Winter Nelis has proved to be the best pollinizer for the Bartlett under all conditions tested. 7. Under valley conditions, the Cornice, Bosc, and Hardy have proved to be satisfactory pollinizers for the Bartlett. Howell, Angouleme, Anjou, and Forelle have also given fair results. 8. Under coastal conditions, Cornice, Clairgeau, and Easter proved satisfactory as pollinizers for the Bartlett. 9. Under Sierra Nevada foothill conditions, Bosc, Cornice, Anjou, Easter, D. Hovey, and Howell are recommended as pollinizers for the Bartlett in the order named. 10. Winter Nelis has been largely self -sterile under all conditions tested but may be successfully pollinated with the Bartlett. 11. Alencon, Bloodgood, B. S. Fox, Comet, Forelle, LeConte, and Madeline have proved to be almost entirely self-sterile under valley conditions. 12. Cornice, Flemish Beauty, Hardy, and Howell may be classed as self -fertile under valley conditions. 13. Angouleme, Anjou, Bosc, Clapp Favorite, Clairgeau, Col. Wilder, Dana Hovey, Easter, Gifford, Glout Morceau, Kieffer, P. Barry, and Seckel may be considered doubtful, and the writers would not recommend that they be planted under valley conditions without provisions for cross-pollination. 14. Under coastal conditions. Clairgeau, Cornice, Howell, and Hardy are almost self -sterile. 15. Bosc, Easter, and Clout Morceau are fairly self -fertile under coastal conditions. 16. Anjou, Bosc, Cornice, D. Hovey, and P. Barry should be con- sidered self -sterile under foothill conditions. 17. Easter may perhaps be classed as self-fertile under foothill conditions; however, attention is here drawn to the fact that in the case of this variety only one season 's results are available. 18. Pear fruits resulting from cross-pollination do not appear to exhibit the same tendency to fall after the June drop as do those resulting from self-pollination. 19. Pollinating agencies such as honey bees are necessary to set a good crop of fruit. 20. One stand of bees should be provided for each acre of orchard. 21. Care should be taken in the arrangement of varieties in the orchard to facilitate cross-pollination and convenience in orchard management. 36 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION A CKNOWLEDGMENTS The writers wish to express their appreciation of the help they have received from the following persons in carrying out this work: Messrs. M. N. Wood, 0. Lilleland, M. J. Heppner, R. Peckham ; J. L. Stahl ; Misses R. M. Amesbury and Edna Russ and to several advanced students in Pomology who rendered assistance in the field and laboratory. Dr. W. L. Howard has given service in suggestions and criticisms. The Earl Fruit Company. Mr. A. L. Wisker of the Loma Rica Ranch, Mr. P. M. Beaser of Chicago Park, Mr. V. T. McCurdy, and Mr. F. Wilcox of Santa Clara Valley, and Mr. Don Searby of Sonoma County have kindly allowed the use of their orchards for certain experiments and have at all times shown a kindly and cooperative- interest in the work. 8m-3,'24.