'-GTIQII OF STOCKS III CITRUS F. By Herbert JohnlTebber* r. of Calif. Agric. Sept. Sta. Bui. 317 THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES OWIVEBSITY OF CALIFORNIA PUBLICATIOH8 COLLEGE OF AGRICULTURE AGRICU TURAL EXPERIMENT STATION BERKELEY, CALIFORNIA SELECTION OF STOCKS IN CITRUS PROPAGATION BY HERBERT JOHN WEBBER ILVIStON OF SUBTROPICAL HORTlCULTUftt COLLEGE OF AGRICULTURE BERKELEVCALIFORNIA BULLETIN No. 317 JANUARY, 1920 UNIVERSITY OF CALIFORNIA PRESS BERKELEY 1920 EXPERIMENT STATION STAFF HEADS or DIVISIONS DAVID P. BARROWS, Ph.D., LL.D., President of the University. THOMAS FORSYTH HUNT, Dean. EDWARD J. WICKSON, Horticulture (Emeritus). WALTER MULFORD, Forestry, Director of Resident Instruction. HERBERT J. WEBBER, Director Agricultural Experiment Station. B. H. CROCHERON, Director of Agricultural Extension. HUBERT E. VAN NORMAN, Vice-Director; Dairy Management. JAMES T. BARRETT, Acting Director of Citrus Experiment Station; Plant Pathology. WILLIAM A. SETCHELL, Botany. MYER E. JAFTA, Nutrition. CHARLES W. WOODWORTH, Entomology. RALPH E. SMITH, Plant Pathology. J. ELIOT COIT, Citriculture. JOHN W. GILMORE, Agronomy. CHARLES F. SHAW, Soil Technology. JOHN W. GREGG, Landscape Gardening and Floriculture. FREDERIC T. BIOLETTI, Viticulture and Enology. WARREN T. CLARKE, Agricultural Extension. JOHN S. BURD, Agricultural Chemistry. CHARLES B. LIPMAN, Soil Chemistry and Bacteriology CLARENCE M. HARING, Veterinary Science and Bacteriology. ERNEST B. BABCOCK, Genetics. GORDON H. TRUE. Animal Husbandry. FRITZ W. WOLL, Animal Nutrition. W. P. KELLEY, Agricultural Chemistry. H. J. QUAYLE, Entomology. ELWOOD MEAD, Rural Institutions H. S. REED, Plant Physiology. J. C. WHITTEN, Pomology. fFRANK ADAMS, Irrigation Investigations. C. L. ROADHOUSE, Dairy Industry. R. L. ADAMS, Farm Management. F. L. GRIFFIN, Agricultural Education. JOHN E. DOUGHERTY, Poultry Husbandry. S. S. ROGERS, Olericulture. L. J. FLETCHER, Agricultural Engineering. EDWIN C. VOORHIES, Assistant to the Dean. t In co-opermtion with office of Public Road* and Rural Engineering, U. 8. Department of Agriculture. SELECTION OF STOCKS IN CITRUS PROPAGATION* BY HERBERT JOHN WEBBER CONTENTS PAGE Forebrief 269 Statement of problem 270 Stocks used in citrus propagation 272 Growing nursery stock 272 Experiments with different-sized nursery trees 273 History of trees used in experiment 273 Comparative tests of large, intermediate, and small nursery trees 275 Discussion of results 282 Variations in sweet and sour orange seedlings 284 Size variations in budding-stock seedlings 290 Examination of evidence and conclusion 295 Recommendations .. - 300 FOREBRIEF Nursery trees even when grown from selected buds taken from selected trees differ greatly in size when they reach transplanting age. Commonly the large trees are sold first and the small trees later when they reach the required size. Large, medium, and small nursery trees of Washington navel and Valencia oranges and Marsh grapefruit grown in comparative tests show that after 2y 2 years in the orchard the large trees remain large, the intermediate remain intermediate, and the small remain small. The evidence indicates that this condition is inherent in the trees and that in planting orchards only the large nursery trees should be used. An examination of sweet and sour orange seedling stock, such as is used for budding, showed the presence of many widely different types. Some of these types were propagated and the trees at the end of 41/2 years still show the same marked difference. Some are fully 5 times as large as others. Yet all such types are used as stocks. Budding on seedling stocks of different types and unknown char- acter of growth is believed to be largely responsible for the different sizes of budded trees developed in the nursery and also for many of the irregularities in size and fruitfulness of orchard trees. * Paper No. 63, University of California, Graduate School of Tropical Agri- culture and Citrus Experiment Station, Riverside, California. DIVISION OF SUBTROPICAL HORTICULTURE 210379 ' COLLEGE OF AGRICULTURE BERKELEY, CAUFORW* 270 UNIVEBSITY OP CALIFORNIA EXPERIMENT STATION This discovery nu-ans that nursery methods should be changed. 1. Seeds for growing nursery stock must be taken from carefully selected good trees of the kind desired. 2. When transplanting from the seed bed to the nursery all small seedlings, probably 50 per cent of the total number, should be dis- carded. 3. Nurseries should be inspected before budding and all small and inferior plants cut out. 4. When budded trees reach the age for transplanting into the orchard, only the good, vigorous-growing ones should be used. The nursery methods suggested will probably be found to be equally applicable and important in the growing of nursery stock of apples, peaches and other trees propagated by budding. If these statements appeal to you as being of interest, read what follows. STATEMENT OF PROBLEM Citrus growers throughout the state have observed great variation in the yield of different trees in the same orchard. This variation is known to be universal even in groves of the same variety that have been planted with the best obtainable nursery trees. Some groves have been studied in which all of the trees were quite uniform and fairly productive, yet a variation in yield uniformly occurred. Other groves were found to be very irregular, containing many trees that made a very unsatisfactory and slow growth, and these were mixed irregularly with others that were somewhat better and still others that were good-growing, vigorous trees, that yielded well. Batchelor and Reed have shown that the yields of trees in the most uniform groves will vary from 30 to 40 per cent of the mean. The margin of profit is not so great in the citrus industry that growers can afford to be indifferent to such conditions. It is of the highest importance that every tree should be a good producer and pay its share of profit. The very careful records of individual tree production that have been made through periods of several years on the same trees by Mr. A. D. Shamel of the U. S. Department of Agri- culture and his assistants have abundantly demonstrated the very real and vital importance of this problem. Citrus growers in general recognize the importance of the problem and are keenly alive to the necessity of remedying the conditions as far as the knowledge available will permit. BULLETIN 317 SELECTION OP STOCKS IN CITRUS PROPAGATION 271 Mr. Shamel has studied the importance of taking buds from good bearing trees known to be productive and true to type and has advo- cated a method of bud selection based on careful tree records. This investigation was of great importance to the industry and the method of bud selection advocated has been generally adopted. There can be no doubt that as emphasized by Shamel the use of buds taken indiscriminately without any care except to see that they were of a certain known variety is responsible for much of the varia- tion in production as well as in type that occurs in orchards. When, however, an analysis is made of the factors influencing yield, it seems probable that this is only one of several factors that need to be considered. The variations in yield of trees of the same variety in the same orchard, planted at the same time and cultivated and treated as nearly alike as possible are likely to be due primarily to one of the follow- ing factors: (1) to variations inherent in the buds due to different heritage; (2) to different kinds and characters of stock used; (3) to the character of the union obtained in the budding or grafting; (4) to differences in the individual environment, especially as to soil, under which the trees are growing; and (5) to accidental and unavoidable differences in the treatment given different trees. The first of these factors has been thoroughly studied and emphasized by Shamel and need be given no further consideration here. The influence of the character of the stock on this variation is believed by the writer to be very important and fundamental, and the discussion of experi- ments and observations on this factor form the basis of this bulletin. The writer desires to explain that this bulletin should be con- sidered largely as a report of progress as the experiments and studies have not been completed and will not be for several years. The results already obtained have begun to attract the attention of growers, how- ever, and the improved nursery methods suggested by the writer are already coming to be used. The general adoption of these methods is believed by the writer to mean so much to the fruit interests of the country that he feels that he is no longer justified in withholding the results and suggestions from publication, even though the evidence is not yet entirely complete. It is important to emphasize that while both the nature of the bud and of the stock is important, all of the variations in yield found in orchards certainly are not due to these factors. The other factors mentioned doubtless also have an important influence on the yields of different trees in orchards. 272 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION STOCKS USED IN CITRUS PROPAGATION The stocks used in citrus propagation in California are mainly seedlings of the sweet orange (Citrus sinsnsis), the sour orange (Citrus Auranthtm), the grape fruit or pomelo (Citrus yrandis) and the Trifoliate orange (Ponrirus trifoliata). Certain varieties of the lemon (Citrus Linumia} such as the Florida rough lemon and the Chinese lemon have been used to some extent but scarcely more than in an experimental way. A discussion of the comparative merits of these various types of stocks will be found in Bulletin 267 of this station, prepared by Messrs. Bonus and Mertz. The sweet and sour orange stocks are the types almost universally used and probably 98 per cent of the groves of California are budded on either one or the other of these two stocks. Almost no attention has been given to the source or kind of seed used in growing the stocks. The seeds of the sweet orange used for growing seedlings to be budded have been taken indiscriminately from almost any sweet orange tree that produced seedy fruit. The sour orange seed used has been obtained mainly from Florida, where it is gathered from numerous seedling trees of the sour oranges that are grown here and there over the state, one or two occurring in almost every yard. This orange is used commonly in Florida as a home fruit in making orange- ade and marmalade. GROWING NURSERY STOCK In growing nursery stock the seed is usually grown in a well prepared seed bed that is protected from full exposure to the sun by a slat shed or by a burlap or cloth shade. The seed is drilled about 1 inch apart in rows about 12 inches apart, and grown in this way for about one year, when they are transplanted into the nursery. At the time of transplanting, the seedlings usually vary greatly in size, ranging from a few inches to a foot or even 18 inches or more in height, depending on the soil in which they are grown and other conditions. This variation in height, however, invariably occurs. In ordinary practice all of the seedlings are transplanted or at most only a few of the smaller ones are discarded. In the nursery the seedlings are planted about 1 foot apart in rows from 3 to 4 feet apart, and must grow a year or more before they reach sufficient size for budding. They are usually planted into the nursery in the spring and budded the following spring a year later. When the budding begins there is usually considerable variation in the BULLETIN 317 SELECTION OP STOCKS IN CITRUS PROPAGATION 273 size of the seedlings and frequently the largest ones that have reached sufficient size are budded and those that are too small are allowed to grow for several months longer, and are budded when they have reached the desired size. After budding the young trees are preferably allowed to grow in the nursery until they are 2 years old from the time of inserting the buds, when they are expected to be ready to set in the grove. At this time, even though they were all budded at the same time and on seedlings of the same age, they commonly vary greatly in size. Citrus trees are commonly sold according to the diameter of trunk an'd it is not an uncommon practice to go through the nursery and first dig and sell the largest trees, the remaining trees being dug and sold when they reach the required size. If time enough is given, the smallest trees from the smallest stocks will finally reach sufficient size and ultimately all find their way into some orchard of the state. Is the small tree that requires a much longer time to reach the required size for transplanting as likely to produce a good productive orchard tree as the vigorous-growing one that first reached the required size? Some growers assert that the small buds make just as good trees as the large buds. Apparently, however, this assertion is not based on definite knowledge, and it would seem to be contrary to our general understanding of nature. It is certainly an important ques- tion to determine as the value of a grove depends upon the character of the trees in it. So far as the writer can learn, no definite study of this question has been made with any orchard fruit and almost no evidence is evailable to assist in reaching a decision. EXPERIMENTS WITH DIFFERENT-SIZED NURSERY TREES History of Trees Used in Experiments. The plans for the investi- gational work at the Citrus Experiment Station included the installa- tion of a long-time fertilizer experiment which should be very carefully planned to avoid all mistakes so far as possible. It was recognized that one of the necessities of the experiment was to secure uniform nursery trees in order to render the trees' in all plots as nearly equal in their yielding capacity as possible and thus reduce to a minimum the differences in yield of the plots due to individual tree variations. The station thus decided to grow its own nursery trees for the experi- ment in order to be certain of the history and treatment of the trees. It was decided to use sweet orange stock for all of the orange and grape- fruit trees in the experiment and sour orange stocks for the lemons. In order to save time seed-bed stock of sweet and of sour orange 274 UNIVERSITY OF CALItX>RNIA EXPERIMENT STATION ready to set in the nursery was purchased and planted in a nursery in the spring of 1914. Attention not having been directed at this time to the possible importance of the source of the seed, no special inquiry was made as to where the seed used in growing the stock was obtained, special care only being taken to see that the stock in each case was not mixed and was of good grade. The sweet orange seed used was probably from sweet seedlings, many of which are still grown in the vicinity of Riverside, where the nursery bed stock was grown. The seed for the sour stock came from Florida but nothing further was definitely ascertained. In each case the seed-bed stock purchased was in good condition and was in no way different so far as could be determined from the ordinary stock of these kinds usually used in the state for propagation. This stock whe i dug from the seed bed was sorted and all of the small seedlings discarded. In this process about 15 per cent of the sweet stocks were discarded and about 25 per cent of the sour stocks. The sour stocks were thicker in the seed bed than were the sweet stocks and the larger percentage discarded as below size was probably due to this cause. The seedlings were planted in rows in the nursery in the ordinary form, the plants being about 12 inches apart in the rows. The nursery throughout was treated as uniformly as possible and made a good growth. The trees were budded in the spring of 1915, about 4000 buds each of Washington navel and Valencia oranges and Marsh grapefruit being inserted on sweet stocks and 4000 Eureka lemons on sour stock. During the process of budding again some of the small weak stocks that had not made a good growth were discarded. It was of primary importance in the experiments to secure buds that could be expected to give good and uniform results, and through the kindness of Mr. A. D. Sharnel and the growers cooperating with him in his bud selection experiments, the buds of all the varieties used were cut from bearing trees on which records of yield and type of fruits produced had be.en kept through a period of 5 years and which were known in every case to be high yielders and of the standard type of each variety. The buds which were all cut by Mr. Shamcl and Mr. W. M. Mertz, then Superintendent of Cultivations in the Citrus Experiment Station, were in the case of the Washington navel and Eureka lemon taken from trees in groves belonging to the National Orange Company at Riverside. The Valencia buds were taken from selected trees on the Slosson grove at Azusa and those of the Marsh grapefruit from the grove of L. V. W. Brown of Riverside. The BULLETIN 317 SELECTION OF STOCKS IN CITRUS PROPAGATION 275 station is under great obligation to all of these gentlemen for their kind and liberal cooperation. The budding was all done during May and occupied a period of about 2 weeks. An excellent stand was obtained and the buds started vigorously and as uniformly as could be expected. There was con- siderable variation in the size of the buds at first due to slight differ- ences in the promptness of different buds in starting growth, but the difference gradually became less marked. Throughout the growth of the nursery it was recognized by all who examined it critically as an exceptionally good and uniform nursery. Comparative Tests with Large, Intermediate, and Small Nursery Trees. In June of 1917 when the buds were two years old they were used in planting the experimental grove on the Experiment Station Farm. A larger number of trees were grown than was needed for the planting and in digging and balling, those buds that were under average size were discarded. About 15 per cent of the trees, it is estimated, were discarded at this time as being undersized. The important fact that the writer desires to emphasize in con- nection with the growing of this lot of nursery trees is that although much more than ordinary care was taken at every step to reduce the amount of variation through using selected good-sized stocks and buds from highly selected trees, that, nevertheless, when the buds were 2 years old and ready to transplant into the grove, they showed considerable variation in size. In examining the nursery at this time with reference to what trees to use in the experimental orchard, the writer was impressed by the extent of the variation in size and con- ceived the idea of testing comparatively the different-sized trees to see whether the size in the nursery could be taken as an indication of what the trees would later do in the permanent orchard. In carrying out this experiment, 18 small, 18 medium, and 18 large trees were chosen by the writer with the assistance of Mr. Mertz from each of the varieties in the nursery Washington navel orange, Valencia orange, Marsh grapefruit, and Eureka lemon. In making these selections of large, medium and small buds it was observed that the greatest range of variation apparently existed among the Wash- ington navel buds and the least among the Valencia buds. While no exact statistical data were obtained from which to derive definite conclusions, the rank of extent of variation among the buds of the 4 varieties appeared to be as follows: (1) Washington navel, (2) 276 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Marsh pomelo, (3) Eureka lemon, (4) Valencia. What this means, if it means anything, cannot now be explained. In order to determine whether the size of the bud growth in any of the chosen plants might be due to accidents to the roots, such as injury by gophers, disease of any kind, or to the so-called "bench root," the trees were dug and transplanted with bare roots (not balled) and the roots of every tree were examined carefully and notes made regarding the growth. None of the trees dug and so examined showed any indication of injury or disease that might be considered as having influenced the growth. In all cases the roots appeared to be thoroughly vigorous and healthy. The trees were planted in soil that had never grown a tree crop and which was considered fairly uniform and suitable for the experi- ment. They were set in rows 24 feet apart and the trees 10 feet apart in the rows. The Washington navels, Valencias, and Marsh grape- fruits were so arranged that in the first row came the 18 large trees, in the second row the 18 small trees, and in the third row the 18 intermediate-sized trees. Shortly after the trees were set in the permanent orchard caliper measurements of the diameter of the trunk of each tree were made at a point about 6 inches above the point of union of bud and stock, the point where the measurements were taken being marked by a band about y 2 inch wide painted on the trunk. The average of these measurements for each different group is given in table 1, which will be discussed later. The .Eureka lemon trees for some reason did not stand the trans- planting very well and so many of them died or were injured that the entire lot was later discarded and taken out. The orchard containing these trees has been given as nearly uniform treatment as possible in order that any variation occurring in the growth of the different trees might be considered as primarily dufi to inherent differences in the trees themselves. " The trees have now been growing in the orchard slightly over 2 years and have made excellent progress. The large trees in every case would now be considered to be rather larger than usual for 2-year- old trees and the intermediate and small trees have in general grown in about the same ratio proportionately to their size. The differences in size that were exhibited in the trees when they were planted are today just as marked as they were in the beginning. The Washington navels all budded on sweet stocks show as in the nursery rather the most striking difference. All of the 18 large trees BULLETIN 317 SELECTION OF STOCKS IN CITRUS PROPAGATION 277 j ? 3 - t o CO CO if Hri C ^ ^ UNIVERSITY OP CALIFORNIA EXPERIMENT STATION continue to be large and this spring (the second spring) bloomed heavily and set some fruit. The intermediate-sized trees still retain their same comparative size and while they produced some flowers have set fruit on only one tree. The small trees, while they look healthy and have grown in about the same proportion as the large trees, are all of them still small. They produced little bloom and no fruit. The proportionate size of these trees can be observed clearly by an exam- ination of Fig. 1. In order to illustrate more clearly the comparative sizes of these three groups of trees, photographs were taken of an individual tree in each group: (large, small, and intermediate) which was judged to represent about the average size of the group. These photographs are reproduced in Fig. 2. The Valencias all budded on sweet stocks show less marked differ- ences in size between the large, intermediate, and small trees than the navels, but the differences are great enough to show clearly, as will be seen by an examination of Fig. 3. The Valencias have in general grown well and within each group of large, small, and inter- mediate trees there is not very wide variation. The comparative size of average trees from each group is illustrated in Fig. 5. The trees in the group of large Valencias developed some bloom last spring (the second spring) but did not set fruit. Some little bloom was developed on trees in the other two groups, but in neither case was it anywhere near so abundant as in the group of large trees, and no fruit set. The Marsh seedless grapefruit trees budded on sweet stocks as in the case of the navels and Valencias continue to show differences in size between the three groups, large, small, and intermediate, but the difference is not so great as in the case of the navels and Valencias. As a whole, the grapefruit trees have not made as good a growth as the orange, and several trees died as a result of the shock of transplanting with "bare root" in July. The fact remains, however, that after 2 years' growth in the orchard, all of the trees continue to retain their same relative size. (Compare Fig. 4.) The comparative size of average trees from each group is shown in Fig. 6. Only a few flowers developed on these grapefruits last spring and but very few fruits set. One of the most reliable indications of comparative growth and size is the change in size of trunk as indicated by the diameter or circumference at a certain definite point, and in Table 1 is given the average caliper measurements of the diameter of the trees of each group of each variety taken July, 1917, a few days after the trees BULLETIN 317 SELECTION OF STOCKS IN CITRUS PROPAGATION 279 IfNIVERSITY OP CAUFORNI.V EXPERIMENT STATION were planted, in comparison with similar average measurements of diameter taken April, 1919, at the same points on each tree trunk, the measurements being in centimeters. TABLE 1 AVERAGE DIAMETER OK TRUNKS (IN CENTIMETERS) OF LARGE, INTERMEDIATE, AND SMALL TREES Navels Large Intermediate Small July, 1917 2.53 1.69 1.29 April, 1919 3.79 2.60 2.16 Percent of increase 49.8 53.8 67.4 Valencia* July, 1917 2.58 l.(51 1.16 April, 1919 3.30 2.52 2.15 Percent of increase 27.9 56.5 85.3 Grapefruit July, 1917 3.11 1.87 1.05 April, 1919 3.29 2.48 1.84 Percent of increase 5.8 32.6 75.2 It will be seen from an examination of the above table that in each group the difference in sizes still remains very marked. The inter- mediate and small groups have made a larger percentage of increase in size as indicated by diameter than have the large trees, but in judging the meaning of these figures it should be remembered that the rate of growth as measured by diameter of trunk and estimated in this way does not show the relative differences very clearly, as much more growth is necessary to cover a large trunk a certain thickness than is required to cover a small trunk the same thickness. In general, it may be said that each group is in size about 2 years behind the next. It will be noted that the intermediate trees in 1919 are in each variety about the same size as the large trees were in 1917 and the small trees in 1919 are about the same size that the intermediate were in 1917. If it were possible to get the volume occupied by each tree this would be a better indication of the comparative size, but no accurate measure of this kind can be obtained. To get as nearly as possible a comparison of this kind, in April, 1919, the top of each tree was measured in three directions, getting the diameter of spread through the top east and west, north and south, and from the first branch up n r BULLETIN 317 SELECTION OP STOCKS IN CITRUS PROP o" 5* ^ ' S p ^ p ff. <-i O 2 3 - S o S'^ &r o g B 3 1 P D toLLCrc UP K*L Hn s?^** CTTRICULTIIR] UNIVERSITY OF CALIFORNIA EXPERIMENT STATION through the top. These figures multiplied together give an arbitrary figure that represents fairly accurately the, comparative volume of the top. As a check on the accuracy of such figures a number of trees were examined and graded in rank of size as accurately as could be done by the eye, using the greatest caution. These judgments corresponded very accurately with the figures obtained by the meas- urements. While admittedly such figures are not accurate measures, they are believed to represent the comparative size of the trees fairly closely. The averages obtained for each group of trees are given in Table 2. TABLE 2 AVERAGE COMPARATIVE SIZE (IN CUBIC INCHES) or TREE TOPS AS INDICATED BY PRODUCT or EAST AND WEST DIAMETER X NORTH AND SOUTH DIAMETER X HEIGHT FROM FIRST BRANCH TO TOP Navels Valencias . Grapefruit Large Intermediate Small 54,174 20,185 12,541 29,003 15,606 12,953 26,343 15,827 10,642 Discussion of Results. The illustrations and data given clearly show that after 2 years' growth in the orchard, the large, intermediate and small trees retain the same relative size that they had when dug from the nursery. An examination made very recently (November 1, 1919), 6 months after the data given were taken, shows clearly that the same conditions still exist. It is possible that in several years some of the intermediate and small trees will make good growth and nearly or quite overtake the large trees in size. However, it seems highly improbable, judging from present indications, that very many of them will do this. The slower growth of the majority would seem to be due to some inherent cause that is not likely to change or to be outgrown. Which ones of the possible factors influencing the size of budded trees is most likely to be responsible for this different growth ? It would not seem to be due in very large degree to differences in treatment or local environment, as all trees in the large, intermediate, and small test rows retain their relative size relationship and this would not be the case had any been greatly injured or retarded by accidental variations in treat- ment or local soil irregularities. Again, they exhibited the same varia- tion when in the nursery in an entirely different soil. Had any local soil condition in the nursery been the cause of the different growth rate, BULLETIN 317 SELECTION OF STOCKS IN CITRUS PROPAGATION 283 3 9 -1 "" 1 1 s - * II ft) "-I erg 284 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION the trees would probably have changed in their relation when trans- planted to new soil. It is not improbable, however, that some of the variation may be due to environment and this possibility will be dis- cussed more fully under another heading. Are the variations due to the character of the union obtained in budding? The evidence at hand is not entirely sufficient to enable us to exclude this factor as a possible cause. The bud unions, however, appear equally well formed on all the trees and this would not seem to be the main cause of the difference in growth. Can it be that the differences observed are due to inherent differ- ences of character in the buds? This would not seem to be the case in view of the fact that all buds used were chosen with great care from trees known to be standard in character and on which production records had been taken through a 5-year period. The only other factor to which the variation might be ascribed is to inherent con- stitutional differences in the root-stocks on which the trees are budded. This immediately leads to the inquiry as to whether the stocks used for propagation are ordinarily sufficiently variable in growth so that such differences might be ascribed to this cause. VARIATIONS IN SWEET AND SOUR ORANGE SEEDLINGS As explained in the early part of this paper, the only distinction ordinarily made in root-stocks is that one chooses either sweet or sour orange, grapefruit, lemon or possibly trifoliate orange. Up to the present time no other choice in general has been exercised. It is well known that there are hundreds of different variations, types or varieties within eaeh of these species or large groups. The great majority of the numerous named varieties of the sweet orange are merely seedling variations that have been propagated by budding. While there are not so many named varieties of the sour orange this is doubtless due to the fact that it is not cultivated extensively as the fruit is not in demand. Fortunately, we have obtained some evidence on this matter through a direct examination of seedlings propagated for nursery purposes. In October, 1914, the writer in company with Messrs. W. M. Mertz and E. E. Thomas, both then of the Citrus Experiment Station, were going through a nursery of seedling sour and sweet oranges of budding size, when our attention was drawn to a type markedly different from the ordinary. This was among the sour orange seedlings. As a collection of varieties was being made at the station, we conceived the idea of selecting the distinct types that we BULLETIN 317 SELECTION OF STOCKS IN CITRUS PROPAGATION 285 Fig. 5. Valencia orange: average-sized trees chosen from test rows of large, medium, and small nursery trees: large, on left; medium, in center; small, on right. Planted in orchard June, 1917, and photographed May, 1919. Fig. 6. Marsh seedless grapefruit: average-sized trees chosen from test rows of large, medium, and small nursery trees : large, on left ; medium, in center ; small, on right. Planted in orchard June, 1917, and photographed May, 1919. could recognize clearly and of testing them to see how great differences existed. Sixteen different types of the sour orange were chosen and 4 different types of the sweet orange. Many more distinct types could doubtless have been selected but it was not recognized at the time that the selection of these types had any more important bearing than merely securing for the variety orchard a few more different forms, all probably worthless. Bud sticks of these 16 sour orange and 4 sweet 286 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION orange seedlings were cut and two trees budded of each for trial in the variety orchard. These trees budded on sour orange stock are now 4Vfe years old from the bud and have been 2y 2 years planted in the variety orchard, thus being the same age as the trees in the experiment described above. Fig. 7. Sour orange (C. E. 8. No. 628). A good, typical type with vigorous growth and excellent foliage and branching characters. Selected as a good stock type. Compare size, branching and foliage with types illustrated in Figs. 8, 9, 10, 11, and 12. An examination of these different types now shows them all to be remarkably distinct from each other in character and size of growth, branching, foliage and other important characters. A series of photo- graphs of 6 of these different types of sour orange is reproduced here to illustrate the great difference in size and character of growth. Compare with each other Figs. 7, 8, 9, 10, 11, and 12. All of the BULLETIN 317 SELECTION OP STOCKS IN CITRUS PROPAGATION 287 trees shown in these illustrations were reduced the same in photo- graphing as shown by the yard stick standing beside each tree. The tree illustrated in Pig. 7 was selected as a good typical type with vigorous growth and good branching and foliage characters. This is probably the only one of the series illustrated that would make a good stock to bud for orchard planting. No grower would assume- that the trees illustrated in Figs. 8, 10, 11, and 12 would give satisfactory results and he would scarcely elect to bud the tree shown in Fig. 9 because it has variegated foliage. The tree in Fig. 8 is a small dwarf Fig. 8. Sour orange (C. E. S. No. 619).* A slow-growing dwarf type. Com- pare size, branching and foliage with types illustrated in Figs. 7, 9, 10, 11, and 12. type with spreading habit and small leaves. In volume, this tree is not over one-fifth of that shown in Fig. 7. The tree in Fig. 10 rep- resents a fine healthy tree but a dwarfish, slow grower with small leaves making a dense foliage. Fig. 12 is similar to Figs. 8 and 10 in its slow growth only. Both of the trees grown of this type show a good many bare limbs as if not thoroughly strong and healthy. It seems to have a weak constitution and to easily shed its leaves, which are characteristically different from those of the other types. The tree shown in Fig. 11 is one of the types having growth of about an intermediate degree of vigor and when seen in comparison with other types of the same age can be recognized easily as of an intermediate grade. If, however, such types were compared only with their own DIVISION OF SUBTROPICAL HORTICULTURE COLLEGE OF AGRICULTURE BERKELEY, CALIFORNIA L >ss UNIVERSITY OF CALIFORNIA EXPERIMENT STATION kind, they could not be recognized as being of any slower growth than ordinary. In some cases the slow dwarfish character of the plant can apparently be recognized by the smaller leaves, shorter internodes and general characters that indicate slow growth, but in very many seedlings of intermediate growth the true character evidently cannot be determined except by a comparison with the growth of other seedlings of the same age grown on the same soil. Fig. 9. Sour orange (C. E. 3. No. 618). A vigorous-growing large type, but differing from tree shown in Fig. 7 in habit of growth and foliage characters. The leaves are variegated. All of the types illustrated and many more can doubtless be found in any ordinary sour orange nursery and are probably regularly budded, the trees sold and planted in permanent orchards. The 4 variations or different types of sweet seedlings selected from the nursery at the same time the sour orange types described above BULLETIN 317 SELECTION OP STOCKS IN CITRUS PROPAGATION 289 were selected, were also propagated and are now 4^-year-old buds. They have proven to be very distinct in character of foliage and rate of growth. All 4 were comparatively slow-growing types as shown by their size now in comparison with buds of other sweet oranges budded at the same time. Of these types 0. E. S. No. 604 had small, short, oblong or eliptical leaves with rounded apex and short petioles. C. E. S. No. 605 had similarly shaped leaves to C. E. S. No. 604, but they were larger and the internodes of the stem were short. C. E. S. No. 606 had long, nearly lanceolate leaves with broadly winger petioles, Fig. 10. Sour orange (C. E. S. No. 627). A slow-growing dwarf tree. while C. E. S. No. 607 had long lanceolate leaves with narrowly winged petioles. These characters have continued to show in the trees and are characteristic differences of the four types. Typical leaves of each of these types are illustrated in Fig. 13 under the numbers indicated above, which are the permanent numbers in the Citrus Experiment Station Collection (C. E. S. numbers). It must be thoroughly understood that the 4 types discussed are given merely as illustrations. A very large number of variations are present in every bunch of sweet orange seedlings and could easily be distinguished and propagated if desired. There is no evidence avail- able that indicates the sour orange to be any more variable than the sweet orange. Lemon seedlings, grapefruit seedlings, indeed seedlings of any citrus species would doubtless show variability in about equal 290 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION proportion. It is, however, fortunately true that seedlings from cer- tain trees are more variable than seedlings from certain other trees, and that we have in this well known condition of nature a reasonable hope that good stock types may ultimately be found that will give progeny grown from seed that will be comparatively uniform through- out and possibly not require the discarding of very large numbers such as suggested in the following section. Fig. 11. Sour orange (C. E. S. No. 625). A. type of medium size and rapidity of growth, also differing from others in foliage and branching characters. SIZE VARIATIONS IN BUDDING STOCK SEEDLINGS In a nursery at the Citrus Experiment Station grown from sour orange seeds obtained from several California trees, an examination made this last spring (April, 1919) showed many variations similar to those illustrated above. An idea of this range of variation may be gained from an examination of Fig. 14 showing 7 contiguous seedlings, each one of which shows different characters even in this young stage. At this time the large individuals in this nursery could have been budded but only about one-fourth of the entire number would have been sufficiently large. BULLETIN 317 SELECTION OF STOCKS IN CITRUS PROPAGATION 291 When the seedlings in this nursery were being transplanted from the seed bed in June, 1918, the smallest were discarded and the remainder were separated in two groups, one of large and the other of small plants, which were planted separately. The group of small plants contained only about one-third of the total number grown. 1 The separation was made entirely from the practical standpoint of getting the large stocks together and may not have been altogether consistent or accurate ; nevertheless, an examination made the next Fig. 12. Sour orange (C. E. S. No. 615). A slow-growing dwarf type of weak constitution. spring (April, 1919) showed the plantings of large and small seedlings to be still markedly different in size. Three hundred and one of the large group were measured and gave an average height of 18.19 inches. They were found to range in height from 5 to 30 inches. It is of interest to know what proportion of these were of various sizes and thus the measurements of the plants are given below (Table 3) grouped in classes differing by 2 inches in height. The measurements were made in inches and half inches. Each class is inclusive. 1 These plants were being grown by Dr. H. B. Frost of the Citrus Experiment Station. J!tL' UNIVERSITY OF CALIFORNIA EXPERIMENT STATION TABLE 3 LARGE SOUR ORANGE NURSERY SEEDLINGS GROUPED IN CLASSES ACCORDING TO HEIGHT eight of classes Number of plnnts in inches of ouch size 3 to 4.5 5 " 6.5 5 7 " 8.5 5 9 " 10.5 9 11 " 12.5 11 13 " 14.5 30 15 " 16.5 37 17 " 18.5