Wp •B. % PtU fltbntrg ^Jortl; (Carolina jiiaie fllolkge 5b)« This book must not be taken from the Library building. 14Sep'fUu 3 S-5 ">* M to o CO « 2§ § 3, i a-a..* ■S'b a C 5 -SS tail a a e o a a t. 2>a"« t, o 3 — < w *3 Eos E o-s © 3-5 •§-a.2e a ~ o y» — They May Be Met 10 / VII New Plums and Prunes in The Process of Making — Some Suggestions on > . .m Which Others May Build 1" / VIII What the Burbank Plums and Prunes Have Earned — The Opportunity Which n a m Improvement Opens Up «' IX Accomplishing the Impossible — The Plumcot — A Cross Which Man Had Said O 7 C Could Never Be Made A io List of Direct Color Photograph Prints 305 Foreword to Volume V Unquestionably the greatest work which Mr. Burbank has done in the line of tree fruits has been with plums and that greatest plum of all, the prune. It has been his purpose in this volume, however, to limit in no wise its value to the plum and prune grower; but, because of the number and completeness of the experiments outlined, it is designed to have a broad, practical worth to the producer of other desirable new fruits, or in fact of any other plants. The reader, by this time, must well realize that Mr. Burbank's methods, all of them, are plant methods rather than flower methods, tree methods or vegetable methods. This book concludes with one of Mr. Burbank's most interesting achievements — the production of the plumcot, a combination between trees of different species, such as men of science had always thought to be impossible. THE EDITORS. 3 "a © © -3 5*. c r I o « fc. -3 >R « R 3 .2 «,S^ R S.S1-, «»S;^ a£a.R L b S &w N S «5 & — a a £■ R c o _ ^ u u aS05?^ ••§ « ~ «■§ fea,R « RcC . 5 » * S *> w »I ^ .*» R -* u w jf S "R ~ S 'E •§ •5< n. a ■- ■- ».*: °E — 3 S ».« «- •- S"R R-"" -. •R 5 a « •» 3 u •R £ c c — fe. i. « 'c-i01 g •— ^ *5 ***§ R <" 2 «*; R A ** k. R~ « a How the Plum Followed The Potato Luther Burbank's First Work in California "HAT you need is a complete rest and a change of climate. Go to California for the winter. This, or something like this, I am told, is a very common prescription of the New York specialist, or for that matter, of physicians everywhere. The value of rest is almost axiomatic, and the benefit to be derived from a change of climate is matter of familiar observation to layman and physician alike. Now I have more than once called attention to the similarity between human beings and plants as to a good many of their hereditary propensities and environmental responses. And the present case furnishes another illustration in point. Rest and change of climate are no less bene- ficial to the plant than to the human patient. And as new surroundings arouse the mind and [Volume V — Chapter I] .HMK7T LIBRARY Jfc C. State College LUTHER BURBANK give a fresh stimulus to the imagination, in the case of human beings both individually and collectively, so the transplantation of a plant to new soil sometimes brings out unsuspected racial tendencies and stimulates variation in such a way as greatly to improve individual specimens and quite to transform their progeny. I had seen instances of this as applied to many different species of plants from the time of my first coming to California. I myself felt the mental uplift of new surroundings, and seemed to find evidence that plants that had come from the east- ern United States, even as I had come, were not unmindful of a similar influence. No species of plant or bird or animal is quite the same on the Atlantic and the Pacific seaboard. We have but to compare specimens of such famil- iar birds as the robin, quail, and meadow-lark, or of plants of any garden variety to note the evi- dence of beginning transformation. My early letters from California told of my astonishment in seeing "great rose trees, thirty feet high; veronica trees, and geranium trees" Of course in those cases where the species has been long resident in California the change has progressed so far that representatives of what were once members of the same clan no longer are to be classified as of the same species. [8] ON THE PLUM All of this, as I say, was observed from the outset when I came to California, just as many another man had observed it. Indeed these things are too patent to escape notice. But, unlike many others, I was impelled to inquire whether some useful application might not be made of the ob- served influence of the California climate on immigrant plants. The Prescription Applied to Plants In following up this idea I was led to apply to a vast coterie of plants the prescription which has become so popular with the present day physician in the treatment of his patients. "Take a rest, and find a complete change of climate. Go to California — and stay there," was the modified form of the prescription as I gave it to the plants of the remotest regions of the globe to which I could send word. And the result of the carrying out of this pre- scription will require some volumes in the telling. For the plants that came to me in response have furnished the chief material out of which a large proportion of my developments of new fruits, grains, grasses, vegetables and flowers have grown. Perhaps foremost in the list of immigrant plants that have had a large share in my life work must be named a little company of plum seedlings that came to me at the very beginning of the period [9] LUTHER BURBANK when I was renouncing the calling of the regular nurseryman and determining to devote my entire attention to the development of new races of plants. The capacity for development shown by this little company of seedlings was nothing less than phenomenal. The change of climate from Japan to Califor- nia was, seemingly, of all things precisely what they needed if they were to put forth their best endeavors to better themselves, and in bettering themselves to confer benefits upon humanity. Perhaps it is not too much to say that the lit- tle company of twelve plum seedlings that came to me with my first successful shipment in 1885 constituted, from an economic standpoint, the most important importation of fruit-bearers ever made at a single time into America. For the im- mediate bud sisters of two of these seedlings con- stitute to-day varieties of plum that are recog- nized as standards everywhere; and from the progeny of these and the others were developed plums of such size and quality as not alone to give this fruit an altogether new standing in the markets of America, but fairly to revolutionize the plum industry in such far away regions as Africa, Australia, New Zealand, our own south- ern states, and the states of the Pacific Coast. [10] c «» p* o"e 2. S'^'o ==" © * 5- 5? re S- h,3«5 s s >3 S5.fi © 5a~ ^~~ •a © &■ sj o ^ re ~ ta — a, a. 3 3- ^ o 2 a. "a • i« ^ B 15 5"s ►s S' 5' 3. co £> 3 ° V- 333 sjgo-ff 5S'" CI K fc> 3 a 3 4> s si, ~. £ 3 LUTHER BURBANK "Rest and a change of climate." It was a magical prescription as applied to the twelve plum seedlings from Japan. And as to the plant physician who gave the prescription — for him personally the results were perhaps as notable as any other events in his life. Already, when scarcely more than a boy in New England, he had had the good fortune to develop a new race of potatoes that had proved of vast economic importance, supplanting all other varieties of its tribe in widely extended regions, and making its way triumphantly round the entire world. Now he was enabled, practically at the outset of his work as a professional plant developer, to introduce races of plums that followed and even out-distanced the potato, revolutionizing a great fruit industry in widely scattered regions of two hemispheres and preparing the way for other conquests in fruit development of which even now the limits are quite unpredictable. Visionary indeed must have been the dreams of the would-be plant developer if his forecast of the possible result of his importation of the twelve little plum seedlings was more than a faint adumbration of the actual denouement. High hopes he had, yet doubtless in this case he builded better than he knew. [12] £ i Typical Satsuma Plum Tree This is an improved Burbank variety of the original Japanese Satsuma, produced by crossing with other species varieties. It retains the red flesh of the Japanese variety. LUTHER BURBANK I recall very vividly the precise stimulus that led me a number of years before the Japanese seedlings were actually imported to turn my eyes toward Japan as the probable source of a new race of plums. A Sailor's Yarn and What Came of It Browsing among the books of the Mercantile Library in San Francisco, I had chanced to come upon an account of the wanderings in Japan of an American sailor, and what particularly held my attention was his mention of a red-fleshed plum of exceptional quality that he had seen and eaten in the Province of Satsuma in southern Japan. That red-fleshed plum appealed to me, and I determined to secure a specimen of it for my own orchards. The sailor reported in his book that he had seen a single plum tree bearing this "blood-plum of Satsuma." But of course the rarity of the fruit made it the more alluring. So in due course when I came to make importations of native seeds, plants, and bulbs from Japan, I urged Mr. Isaac Bunting, an English bulb dealer in Yoko- hama who collected these for me, to visit the southern part ol that country and make a par- ticular effort to procure with others some of the red-fleshed plums. [14J ON THE PLUM Mr. Bunting complied with my request, but, vastly to my disappointment, the first lot of young trees he shipped to me arrived (Nov. 5, 1884) in such condition that I despaired of doing any- thing with them. I immediately sent a request for another shipment, and gave definite instruc- tions as to packing. A little over a year later, on Dec. 20, 1885, there arrived the twelve seedlings to which I have al- ready referred. And this time, to my great sat- isfaction, the tiny trees were found in good condition. A few days after these seedlings were received, I purchased the Gold Ridge Farm at Sebastopol, eight miles from my Santa Rosa place, and here as soon as they were large enough, cions from the twelve little strangers were grafted on to older trees and thus brought early to maturity. One of them bore fruit the following summer and the others in the course of one or two suc- ceeding seasons. And so well had the little immigrants re- sponded to the stimulus of new surroundings that each one of them revealed, I make no doubt, the very fullest possibilities of its heritage. More than that of course was impossible, but it may well be doubted whether any one of the com- pany would have produced fruit quite of the same [15] LUTHER BURBANK order had it been nurtured in the climate and fed from the soil to which its ancestors had been habituated. Rest and a change of climate could not give new hereditary possibilities, but they could be instrumental in bringing dormant possibilities to full realization. How Rest Stimulates Growth Possibly this statement requires a further word of explication, for I think we have not else- where emphasized — though the subject has been once or twice mentioned — the value of rest in en- hancing the vitality of plants and in giving them new capacity for growth. Of course nothing is more familiar — and therefore nothing seems more commonplace — than the annual dormancy of plant life in gen- eral throughout the winter season in temperate zones. But until somewhat recently no one had par- ticularly associated such dormancy with the vig- orous growth of the reviving plants in the spring- time. It was familiarly known that tropical plants keep up their growth, even if somewhat intermit- tently, throughout the year; and it was assumed that the plants of temperate zones had taken on the habit of winter rest merely because this habit [16] The Fruit of the Burbank Plum Mr. Barbank has produced thousands of plums, and has introduced three score varieties, but only one of these bears the name of "Burbank." This is the plum here shown which was grown by Mr. Burbank on a tree introduced from Japan. It is grown to-day in enormous quantities in the aggre- gate, under the most diversified conditions of soil and climate all over the world. LUTHER BURBANK was forced upon them by the exigencies of cli- mate. And indeed, there is no reason to doubt that such was really the origin of the habit of winter rest. We have had at least one illustra- tion, in the case of the winter rhubarb, of the readiness with which a plant resumes the habit of perennial activity. We suggested in that connection that peren- nial growth is the normal and primitive habit of the plant; and there is no occasion to modify that suggestion. But even though the winter sleep of the plant was forced upon it, there is reason to believe that the habit thus inculcated is of great utility in con- serving the energies of the plant and promoting its vital efficiency. The experiments that justify this conclusion have been made in recent years by a number of different botanists, and they have conclusively demonstrated that it is quite the rule for a plant to develop exceptional powers of growth imme- diately after it comes out of a period of dormancy induced artificially. Plants narcotized with the fumes of ether or chloroform, for example, are rendered quite in- capable of growth while subjected to the fumes. They are seemingly stupefied and their condi- tion of dormancy or lack of vital activity is curi- [18] a s B"o S <* s «a a H re o <* S re a 2 3 > 3 J re rn. re — . re j* * ~~S £ » * B-5 re to t-j -* jj.k, ® B-BS 2 re a s a < 2 : a B ~- B i s"s: re : re >' •i re S ft ft » i o a, re re 2. 3" • in 3* ~ _ re ' " n l^a •?» 3 2. 3 ->• H ~k re s> a a- © a a'B)| g 2 LUTHER BURBANK ^f as to the exceptional qualities that they presently *0 manifested. ^ After all, it is more important to know just *• ^ what the little seedlings achieved than to attempt to say just what share different causes had in the achievement. In view of the very remarkable results, it should perhaps be explained that the Japanese plums are in general subject to great variation; the reason being that it has been the custom, which still prevails pretty largely, to raise the fruit from seed instead of propagating it by grafting, as is done in this country and in Europe. So the little seedlings that came to me were doubtless of mixed heritage. In a word they had been produced by cross-fertilization between races not thoroughly fixed. In dealing with them I profited by experi- ments that had been made, doubtless quite unwit- tingly, and with the aid only of insect pollenizers, in Japan in the preceding plant generation. In any event, it was demonstrated in due course that the seedlings were a very remarkable lot. Each of the twelve produced fruit of inter- esting character, and two of them showed a prod- uct altogether out of the ordinary. Both of these were introduced in 1889, and met with immediate and permanent success. [24] LUTHER BURBANK The one first offered to the public bore fruit in 1886, the summer after its importation. In my year book I described this fruit as "very large, conical, heart-shaped, red with white bloom; very good." In point of fact the appearance of the plum, its size, and its delightful flavor and aroma at once proclaimed it as an exceedingly valuable acquisition. Naturally I was pleased with it, and showed it to a number of prominent horticulturists who visited my experiment orchard during the next two or three years. Among these visitors was Professor H. E. Van Deman, Pomologist, U. S. Department of Agriculture. Professor Van Deman was much interested in this new fruit and suggested that it should be introduced immedi- ately. After talking over its qualities thoroughly, he requested that upon its introduction it be given the name of "Burbank." Accordingly in 1889 this new fruit was offered to the public as the Burbank Plum. The Career of an Immigrant The story of the ultimate success of this fruit will be told statistically in another connection. Suffice it here that the Burbank plum presently outranked all others as a California shipping [26] H <* 5 g a- a ft ^5 ft a. ft ? <6 ■e a a 5' 5 n H 3 3 -T 0 a, fS B" it K 1 0* a a B ■a B 2 to o to B 3 Z' It iQ B 5 a- © ■© 1! •a ^>' & a a. ft 5 * hi St)8 3 B ~. a •— 3 3 S __ ~ s 1) ^ 5 B ss 3 B e 1 s » ft n s 2 6 n — . ft a. a. - ■y. B ■^ "3 0 i 0 5 - p* n 1 LUTHER BURBANK plum, and at the present time in the east is the most popular and most generally offered for sale in the markets. Last year 125 carloads of this fruit were shipped to the eastern market from California. Of course the career of this plum, like that of every other young fruit, has been subject to vicissitudes. Some who have attempted to grow it in cli- mates to which it is not adapted have considered it of small value. Yet there are few climates where it does not thrive; and for every orchardist who has tried it and found it wanting there are scores, throughout the world, who have been as- tonished and delighted at its value and have planted large portions of their orchard with this variety. Although there are certain latitudes, certain conditions of humidity, and certain conditions of temperature under which it will not thrive, the Burbank has been able to adapt itself to more varied conditions than any other plum. By way of illustration, I may cite a letter from an extensive grower at North East, Pa., who states that his orchard of Burbank trees survived the extreme cold of the winter of 1912-1913, during which the thermometer registered as low as thirty degrees below zero, and at the usual time in the [28] ON THE PLUM spring put forth blossoms abundantly that bore their habitual good crop of fruit. Compare with this the opposite conditions of climate in some of our more southern states, and in some sections of Africa where the Burbank is extensively grown — and we have a story of re- markable adaptability on the part of this plum. The Blood-Plum Satsuma The other notable plant among the twelve seedlings was a representative of the race about which the sailor had written and about which I had read with such interest years before in the San Francisco Library. This was, in short, a plum with red flesh, some- thing hitherto unknown among the plums of Eu- rope or America. Red flesh in a plum is a character so conspic- uous that it is not likely to escape attention even of the least observing. And my red plum had other qualities that made it well worthy of intro- duction. It first came into bearing in 1887, and two years later it was introduced under the name of Satsuma — the name being suggested, as was that of its companion the Burbank, by Professor H. E. Van Deman. The name seemed highly ap- propriate because it was the name of the province from which the plum had come. Satsuma and its greatly improved hybrid de- [29] LUTHER BURBANK scendants have been most welcome additions to the fruits of America. The original Satsuma is especially popular in Southern California and in the more eastern of the Gulf States as well as in the Southern hem- isphere. It is a good healthy tree with rather narrow pointed leaves of medium size. It is not so adaptable to varying climates or conditions as the Burbank, being better suited to temperate and semi-tropical climates. Nevertheless it fruits well in some parts of New England. It is not large enough for general shipping, but is grown mostly for home use. The fruit is globular and usually averages nearly two inches in diameter. The skin is red, covered with a thick pale blue bloom. The flesh is a dark purplish red, firm and of excellent qual- ity when thoroughly ripe, though not to be com- pared with some of the hybrids which have been produced from it. It is esteemed for the table when fresh and for making jellies and jams. Such peculiar interest attaches to this unique plum that I will quote an account of it given in "The Plums of New York," published in 1910: "There is a group of several varieties of Tri- flora plums unique in having the flesh deep red in color and very firm and juicy. Of these red- fleshed plums, Satsuma was the first toJ^lhtro- [30] *5ggcO^ 8"? a o «a T 2 A o " B s a "• a g - a 3 a a ST ^ a. _ -• B -. ° n> a S ' ■ a;- S 2 2$ a s '** a* a s e a R a' ~ 2 (*' ~ a a,S.o =• B 3 ^ H B ^ a <»^ ft a sl- »» ^ a ** w S a £ * : a o w a; a. £r OS „ R a a "* 3< "-« R R LUTHER BURBANK duced into fruit-growing America and is one of the parents of most of the others. While the fruit is not as large nor as handsome in color as in some of its offspring, it is still one of the best va- rieties for quality of fruit and its trees are pos- sibly as good as those of any of the other sorts of red-fleshed Trifloras. "Satsuma, besides being one of the best of its class in quality for either dessert or culinary pur- poses, keeps and ships very well, and if the plums are of sufficient size and have been allowed to color properly, the variety makes a good show- ing on the markets. Too often, however, it is so unattractive as it reaches the market that it does not sell well. In the South the plums are said to be much attacked by brown-rot, but they are not more susceptible here than other plums. The trees are rather above the average for the species in size, habit, health, hardiness, and productive- ness though they bear sparingly when young. "They bloom early in the season and are dis- tinguished from other Triflora sorts by having many spurs and short limbs along the main branches. "In 1887 Burbank's tree was the only one beam- ing in America, but since then it has been tested in all of the large plum regions, having been in- troduced by Burbank in 1889. In 1897 it was [32] The Sultan Plum Tree The tree in the background shows the typical conforma- tion of the Sultan. The branch that Mr. Burbank's helper is holding suggests that among its other good qualities the Sultan is a prolific bearer. Mr. Burbank has produced a good many bet- ter plums in more recent years, but the Sultan must still be considered a very meritorious fruit. LUTHER BURBANK added to the fruit catalog list of the American Pomological Society. "Even though this plum is very distinct, with its solid red flesh, it is much confused with other sorts. A Japanese in a letter to J. P. Berckmans says 'Beni-smomo comprises a group of red- fleshed plums. In Satsuma, my native home, Hon-smomo and Yone-smomo are the most noted and familiar fruits of this group; the first is the smallest in size and deepest in color, while the second is the largest and most highly esteemed. In some districts, plums in this group are called Uchi-Beni, which means red inside.* "Tree medium to large, vigorous, upright- spreading, usually quite hardy, moderately pro- ductive, bearing heavier crops as the trees be- come older. "Fruit mid-season or later; one and seven- eighths inches by two inches in size, variable in shape, ranging from roundish-cordate to some- what oblate, flattened at the base; color dark dull red, with thin bloom; dots numerous, of medium size, russet, somewhat conspicuous, clustered about the apex, stem slender, three-eighths inch long, glabrous; skin of medium thickness and toughness, semi-adherent; flesh dark purplish- red, juicy, tender at the skin, becoming tough at the center, sweet, with an almond-like flavor; of [34] a 5 *. a «. 2 wg 2 3- a. a <* 3° S'C8 ca 3 & h* a. w 5 LUTHER BURBANK good quality; stone semi-clinging or clinging, seven-eighths inch by five-eighths inch in size, oval, strongly pointed, rough, tinged red; ventral suture narrow, winged, dorsal suture grooved." Descendants of the Satsuma The red-fleshed plums because of their unique appearance have found a place especially in home orchards. On some markets, particularly in the northern part of the United States and Canada, there is a good demand for them as ship- pers. Eastern markets of the United States pre- fer plums of a lighter colored flesh. So far as known, no one else has taken up the work of the production of red-fleshed plums. Nine others, however, in addition to Satsuma, have been introduced from my farms. These in- clude Delaware, Santa Rosa, Beauty, Apple, Du- arte, Hermosillo, Rubio, Prize, and Sultan. The quality of some of the red plums is un- excelled by any others, and they are especially liked for making jellies, jams, etc. They add a richness of color which is not obtainable with any other tree fruit. Often the red-fleshed plums are added to other fruits for the purpose of pro- ducing an attractive color and desirable flavor. They also serve a useful purpose in furnishing a pleasing variety of fruits. The Satsuma and Burbank were the only two [36] t> -"a <« B "O rs ft •** '■"' 3 3 S5. _ 3 £i O ft 3 ^ ~ K * i a 3 ~ ° ■ — 2. 2 2 "> « . ?g * S.S a»c3 5o ? £§' C -s. 3 3-3 P * § Ca«a B ft Qi — a a* "*s ?*§ s a » 2 s » i 5 « n a, i S-3 o £.< g 3 O < ~° J re -iit) J H va: 3-H 3 2 LUTHER BURBANK among my twelve seedlings that were directly in- troduced, although sundry of the others subse- quently had a share in the production of hybrid races. It should be recalled also that I had some- what earlier introduced three plums of Oriental origin, namely, the Abundance, Ghabot, and Berckmans, that were also the direct product of Oriental stock, grown and fruited by me from seedlings purchased from other importers. I have not dwelt at length on them here be- cause they seem of relatively less importance in retrospect than they appeared at the time when they were introduced. Together with the Burbank and Satsuma they make up a group of five plums that were grown from imported seedlings, without hybridization, that ultimately came to be known wherever plums are grown. But the Satsuma was the last plum introduced by me that was grown without hybridization from imported stock. My next and all subsequent introductions were new races produced by crossing and hybridiza- tion, combining the heredities of widely varying species, and selecting the best from among thou- sands of seedlings. The story of the experiments through which these new races were developed belongs to the next chapter. [38] Four Burbank Plums, and How They Were Made Methods Which Brought Unprecedented Success NATURE tells every secret once," says Em- erson. And this, after all, is only the poet's way of saying that there must always be someone who is first to listen to the secrets that Nature is telling every hour. Once in my life, if I mistake not, I was privi- leged to listen to a secret that others had refused to hear or had heard but vaguely. Doubtless it had been whispered or half-whispered in many another ear. But in my ear Nature chanted this secret perpetually, insistently, and in compelling measure. She told and re-told it to me until I had no choice but to listen. The secret was this: New species of animals and plants originate through the hybridization of old species. [Volume V — Chapter II] LUTHER BURBANK Stated otherwise, this means that so-called "spontaneous" variation, which Darwin found mysterious, is really due, or for the most part due, to the bringing together of diverse ancestral strains through cross-fertilization. It is varieties thus developed that furnish ma- terial for the operation of Natural Selection, through which — as Darwin taught us — new spe- cies have been evolved in the past and are still being evolved. I think I had more than half fathomed this mighty secret before I had made extensive ex- periments in plant hybridization. But in any event I had not gone far with my experiments in plant development before I found evidence pil- ing up on every side to reassure me that what I had heard was no illusory voice but the voice of Nature herself. Doubtless no single tribe of plants served me better in this connection, or were more obviously the medium through which Nature's great secret was revealed to me and corroborated, than the tribe of plums. And in the forefront of the com- pany, in this connection, must be named the twelve little seedlings from Japan. If I had entertained any doubt as to the cor- rectness of my premonitions, the results achieved when these Japanese plums were allied with other [40] 2. 2.* ' 2^3 O'O B I » 5. 3 ' "2 » « Co s, . t a ^5.S 5-§ a. •a b g- •» S ~"^> a* a «s 2 .(3< » -) Sb?s o a e a,. al« •5 c & S3- >«3 5" > • &* a< 2 n* a S * it) s S*^ t> _ J» a srffSS ™ Km *1 LUTHER BURBANK they been important. An educational influence has radiated from these experiments, as per- formed here on my farms at Santa Rosa and Se- bastopol. It is not too much to say that they have had a leading share in disseminating new views regarding plant evolution — and, reasoning from analogy, animal evolution as well. The new varieties of plums have largely mod- ified and expanded an extensive industry, mak- ing plums of the finest quality an every-day food for the masses instead of a luxury. The lessons inculcated by the experiments in hybridization through which these new races have been devel- oped have served as a guide to countless other experiments in plant breeding, and have made views that seemed heretical thirty years ago seem commonplace matter of fact to-day. They have almost revolutionized the work of plant improvement. The materials through which this really sig- nificant modification both in the practice and the theory of plant development was brought about were drawn from five great divisions of the globe — five regions with different soils, climates, and natural conditions, and with a human population of correspondingly divergent habits and tastes. And in return the new races of Burbank plums, prunes, and plumcots are being sent back [52] ON THE FOUR BEST PLUMS vastly modified and improved to the diverse re- gions from which their ancestors came, and in addition are making their way in some regions where no plum could be grown on a commercial scale before. Material from the Orient Clearly to apprehend the conditions of the problem that confronted me when I first under- took on a comprehensive scale to put my ideas as to plant development into execution, it is desir- able to note very briefly the characteristics of the different races of plums that were brought to the Santa Rosa melting-pot. Let me outline them. Reference has already been made more than once to the Japanese seedlings. The plums from this source, like those from every other, typify in many respects the people among whom they were developed. Modified to meet the needs of an is- land people occupying a relatively small territory which nevertheless compasses many degrees of latitude, the Japanese plums differ a good deal among themselves as to their hardiness. But in general they are rapid growers, with early and abundant bearing qualities, and unusual adapta- bility to wide ranges of climate. The fruit is unique in form. It averages large in size, with a high percentage of flesh to stone, and with both skin and flesh of high color. [53] LUTHER BURBANK The brilliant purple, crimson, and pink shades shown by some of the modern hybrids are a trib- ute to the Japanese members of their ancestral stock. But while the Japanese plums have these sig- nal merits they are not without their faults. Many of them are small and most of them lack flavor. Freestone qualities have not been developed in the slightest degree. Many of them lack timeli- ness of bearing; others bloom so early that the crop is often destroyed by late spring frosts or heavy rains. Moreover the Japanese often eat plums that are hard and green, preserving them by pickling; therefore they sometimes neglect to appreciate the sweetness and flavor of the fruit. These, obviously, are defects that the plant improver must bear constantly in mind when he sets out to separate and recombine the traits of his company of plums. The Chinese, near neighbors of the Japanese, developed plums of a different type. The Jap- anese plum is known as Prunus tri flora; it per- haps originated or was developed in Korea, South- ern Siberia, and Northern China. But the Chi- nese apricot-plum, known to the botanist as Prunus simonii, must have originated in some semi-tropical climate. It has form and color sug- [54] <^ ri n w » 1 3 ^"O a- 2. Is n> 3 <« n £*. a, * c ^ ■*> s © .-» "*• » a S o <*> 3 S "> 3 3 -. a W?S 3 >o 2 2 Ss §S i Co o c LUTHER BURBANK gestive of a tomato. It perhaps originated near the native home of the apricot, to which fruit it appears to be somewhat more closely related than to other plums. The fruits of China, apparently, have not been greatly modified for many centuries. They there- fore tend to fixity. Indeed, they furnish a typical example of the way in which the conservatism of a race may be stamped upon its fruit. Or is it that people and plants alike are conservative be- cause of the climatic conditions that environ them? In any event, the Chinese plum, when hybrid- ized with other species of plums, brings to the union characteristics that are highly important. Thus the Chinese plum has a delightful aroma, it is of unique form and rich color, and the stone is very small in proportion to the flesh. On the other hand this plum is chiefly adapted to arid, semi-tropical climates; the fruit is likely to remain bitter, and it may crack so badly as to be utterly worthless. Fortunately the merits may be retained, and the faults eliminated, in the hybrid progeny. Materials from Europe and America The European plum manifests no less mark- edly than the oriental one the tastes of the peo- ple by whom it has been developed. F561 **8 ©■ Is K 3- s. s I » 8 a a-* a * I n 8 a- £ ©•<» 8&~*SS* 8 fgll" © 3 LUTHER BURBANK European fruit growers have had in mind many and diverse qualities of fruit, and they have developed diversified races of plums. The original species from which these have grown is known as Prunus domestica. Doubtless at a time sufficiently remote this plum was of the same ancestral stock with the Japanese and Chinese species. But many cen- turies of modification to meet the tastes of the Caucasian races have so altered it that it would be difficult to say what were its original charac- teristics. The Western races, carrying the plum with them to different regions, developed widely dif- ferent tastes and inclinations, and the plums that were ultimately grown to meet the tastes are of course equally diversified in quality. Some are large and some small; some exquisitely sweet, others relatively sour. Some are adapted to eat- ing while fresh; others are most useful for dry- ing or for canning. In a word, the races to which the western plum has catered are of complex lineage; they live in widely varying climates and under greatly diver- sified conditions. The Caucasian lives everywhere and his fruits have adapted themselves to his condition. Summarized in a few words, the advantages [58] Tri-Parental Seedlings This crossbred plum has the color of the Satsuma, the general appearance of the Burbank, and the shape and form of the Kelsey; and these are the parental strains which are represented in its heritage. LUTHER BURBANK of the European plums are: wide diversity as to colors, qualities, and flavors, and adaptability to a wide range of climate. The faults of the European plums are these: the stone is quite generally too large for the size of the fruit; the fruit itself in most cases is too juicy — sometimes absolutely watery — and there is a wide range of textures to be avoided, including stringiness, brittleness, and sponginess. More- over, large size and exquisite quality are seldom combined. The green gage, the standard of ex- cellence among the hardier European plums, is quite small, and the tree is unproductive. And the large European plums are quite often lack- ing in texture and flavor. Size and quality are not correlatives in the case of these plums. It must be especially noted, however, that it is the European plum, in some of its varieties, that has the qualities of large sugar production that permits it to dry readily in the sun without fermentation. This variety of plum, known as the prune, has been the means of building up a great world industry. At the moment, however, we are chiefly concerned with the plums in gen- eral rather than with this particular race. There remain the American plums — that is to say the plums that were found growing in Amer- [60] g 2 "a <« s a, co is ~. e -. ft -5.2 ft> S. c. 3 n St- LUTHER BURBANK ica at the time of* European discovery. There are several quite distinct species of these indigenous plums. They grow far to the north, and perhaps their most important charac- teristic is their hardiness. Some of them resist the scorching heat of tropical America; others thrive and bear in the short seasons of the snowy north. With hardiness of tree has been developed a strain of productiveness. Various wild plums often cover the ground in the fall with layers of ripened fruit. Notwithstanding this, however, the crop is uncertain, some of the thriftiest trees proving un- productive in certain seasons, and the fruit is always inferior in size. Many of the American plums are of fine qual- ity, even in the wild state. Yet their faults are almost as numerous as their virtues. The trees are generally small, not usually large enough to make good commercial orchard trees. In form, too, the trees are defective. And the fruit, not- withstanding its excellent flavor, is often soft and watery, quite lacking shipping quality. In the Melting Pot Obviously, then, the plums of each country offer certain good qualities and present certain defects. To take the characteristics from the plums of [62] A Faulty Beauty This fruit is a Blood Plumcot; the plumcot being, it will be recalled, a cross between the plum and the apricot. This particular variety shows its Chinese parentage in its faulty habit of cracking; which renders it utterly useless for marketing pur- poses, notwithstanding the lusciousness of its flesh. LUTHER BURBANK each country and combine them in different va- rieties; to eliminate the faults as far as possible; to select and test the best among the millions of seedlings produced from the various combina- tions; to redistribute these fruits when produced and thoroughly tested, sending them back greatly improved, their good qualities retained and others added — this has been the work of the plant orig- inator in the attempt to produce an ideal plum. Having for working material plums in which different combinations of qualities have been de- veloped for the most part unconsciously from dif- ferent races, our task was a consciously scientific selection. We must strive to produce, in a few decades, changes comparable to those that had been wrought in the course of centuries through un- conscious selection by many peoples under widely diversified climates and conditions. Conscious systematic selection was to amalgamate all the best qualities of plums and plum-like fruits; those that bore the imprint of the conservatism of the Chinese race, the insularity of the Japanese, the diversity of the European, the nomadism of the Persians, the hardiness and variability of the American. The best was to be taken from each, and the good qualities developed in five widely varying [64J •— ft ft 2 la*"' ©isse? ~s 3 n> i 3 -» »5.H C ** > 3-s-S" 3 ft n *« ft s53 "as *«% a C/3 a SO © & K 3 LUTHER BURBANK geographical territories were to be assembled, combined, sifted, and selected to produce fruit having the stability, novelty, variety, piquancy, hardiness, beauty and shipping qualities, and adaptability to new conditions and uses of the races that had left their imprint in varying meas- ure on the ancestral stocks. Viewing the work in retrospect, I assuredly have no cause to regret that it was undertaken, yet it has been a most laborious task. Doubtless the time expended on the plum has been at least as great as that devoted to any other single line of my investigations. The labor, es- pecially in grafting, budding, testing, and select- ing, has probably been greater than that devoted to any other plant origination, with the possible exception of the spineless cactus. Roughly speaking, I might perhaps say that the plum experiments represent, first and last, something about one-tenth of the total expendi- ture for my experimental work. In importance, up to the present time, judged by results, the work with the plum may repre- sent perhaps one-sixth of all my work; in extent and variety, perhaps one-tenth of the total. In commercial value, up to the present, perhaps the plums may be credited with one-third; but they will rank by no means so high when the final [66] a «3 _ a a 3 © c» -» a* i. s B n n ~i3a S.^'S'S'a'S' o ^ C ^Q ft § » a •72*a i 'Hi g n a. I 09 a' n* c n n C; "* "> a «2. » "j»^ 2 * a § «• 3 «"» 2 B S « 3 a.-8* n> (?© 1 "S3 a. t SI'S 5. ? h ■a*5 5 a* B a- 2 5 r. Th «s3C,s; i 3 g 3 £ O 3 o a c 3 LUTHER BURBANK ledger is balanced, for there are other produc- tions, among them the cactus, that loom large in prospective value. So in the end perhaps the economic rank of the plums, among the total of my plant produc- tions, will not be more than one-twentieth. Yet when I state that from among the almost countless new varieties that have developed in my plum orchard, sixty-two have been thought worthy of introduction, and that some thousands of races are still undergoing tests, an inkling of the work involved will be gained. And when I add that the Burbank plums make up about one- third of the total export of the plums from Cali- fornia year by year, and that my proteges are as popular in South Africa, in Australia, and in nu- merous other remote regions of the globe as they are in the state where they originated, something of the economic importance of the experiments in plum development will be revealed. Specific Results Some glimpses have been given in earlier chapters of the methods of experimentation through which particular races of new plums have been developed; and fuller details of the methods and results will be given in subsequent chapters of the present volume. Here let me briefly outline some of the earlier results of my [68] ■sJm '.-Jm^ Formosa Plum Tree in Bloom This plum shows the influ- ence of its Japanese parents, among other ways, by the habit of bearing fruit on the new wood as well as on the old. LUTHER BURBANK effort at hybridizing the diversified races that were brought together for the purpose of these comprehensive experiments. I have said that some notable results were obtained almost from the outset. As illustrating this, it may be recalled that, whereas the first hybridizations between the Jap- anese seedlings and plums of European and American stock were made in 1888, there were no fewer than six varieties of hybrids in my orchard in the season of 1893, only five years later, that were considered worthy of introduction and that were able to take rank at once as superior in some regards to any plums at that time known. Two of these, named respectively the Dela- ware and the Hale, were hybrids of a double ori- ental stock, one parent being the Kelsey, a Jap- anese plum introduced by the orchardist whose name it bears, and the other my Japanese Satsuma. A third was a hybrid between a Japanese plum named the Sweet Botan, or Golden, and the Rob- inson, an American plum of the Chickasaw race. Two others were crosses of the Robinson and Abundance. The sixth was a cross between the Kelsey and the Burbank, its ancestral strains being therefore Japanese. This plum was first named Perfection, [70] ON THE FOUR BEST PLUMS but.it was afterward renamed the Wickson, in honor of Professor Edward J. Wickson of the University of California. All these are exceptional plums, but the Wick- son is pre-eminent in virtue of its combination of good qualities. The tree grows upright, largely in vase form. It branches gracefully, and it is productive almost to a fault. The fruit is large and handsome. From the time when it is half grown to a few days before ripening it is pearly white in color, but all at once numerous pink dots appear, and in a few days it has turned to green flushed with crimson with a heavy white bloom. The stone is small and the flesh of fine texture, firm and sugary and delicious. It will keep two weeks or more after ripening; or it can be picked when hard and white, and will color and ripen almost as well as if left on the tree. The general excellence of this fruit may per- haps best be gauged by the statement that last year more than one hundred carloads of this va- riety alone were shipped from California to the eastern markets. Difficulties Overcome But while these notable successes attended the earliest hybridizing efforts, it must not be sup- posed that the experiment was carried out with- out difficulty. [71] LUTHER BURBANK In point of fact it was not easy to effect the cross between the Japanese plums and the Euro- pean varieties. Some varieties refused to com- bine; and probably not more than one in a hun- dred of these crosses proved in any way satis- factory. When a hybrid is produced, the traits of the Japanese plum usually seem prepotent, though in some cases the balance between the two is fairly good. Whereas the hybrids of the first generation sometimes produce fairly good fruits, as a rule their fruit is rather soft and acid. The full pos- sibilities are revealed only in later generations, and in particular after other species and varie- ties of plums have been brought into the com- bination. As rapidly as possible the hybridizations were extended, until forty-three races of plums had been used. In successive generations the various strains were intermingled until they were com- plex beyond computation or accurate recording. The original seedlings were used as stocks for grafting the cions of new seedlings year by year. To this day they stand in the original rows, al- though little is left of the original trees except the trunk and the bases of the branches. Each season, the grafts that have been proved to be of [72] a <» ft « O.J Co m 3" as a* ft re ■« Vft Q « 5.3 S.1 r1* *> 5 s- N "* re -» re * ft 2 8 <» 2. "1 ^ <* • ft a o.=. < 3 2 5° S3 5. as a o 3 B . " „ 3 S s <* ^ o ft -• 3~«. • p B So <» S O 3 0 re 3* 3- 3-I3 re h J o <9 rJ « -J • n ■iilMirere*: i re'S.S* •? ° 3 ? C ° • to a % g ? B £ CO «: ft BV 3* 5- ' O ~^- 3 re CO » s LUTHER BURBANK no value are removed and cions from new seed- lings are put in their place. Most of the trees have borne from ten to twenty sets of grafts. Details given in other chapters will enable the reader to follow in imagination the process of blending and selection through which, on the av- erage, year by year a better and better combina- tion of qualities was effected among my plum proteges. Almost as a matter of course, there ultimately appeared individuals that far surpassed most of the earlier hybrids in one or many desired qualities. The Quartette of "Best" Plums And in the course of years there were found at least three new varieties, all of the most com- plex ancestry, that excelled any of their forerun- ners with the single exception of the Wickson. The three new claimants, which stand as the finest products of plum development up to date, have been named the Santa Rosa, the Formosa, and Beauty. These with the Wickson may be listed as un- qualifiedly the best products of the experiments in plum hybridization up to date — a quartette of plums of matchless quality. It must be understood, however, that there are [74] e» 1g o> *-2a S £ K, l » °- S =3" s o: S5 3*; S.ss ft 2* s » 3 >-0 lis* v 5.S-? 0, ** ** a ET tea05 .3 = e 5 S § 3 S 3 >f n> i B f * 3 i 8*s 3 < « c o o , O n» " •a 3>£e* S 2 I S o ? 3 c* ft © a c 3 LUTHER BURBANK unfulfilled possibilities of future development among the hybrids of my plum orchard. Selection has gone on year after year until the plums that remain are all of complex ancestry and of fine individual quality. New crossings between the almost numberless varieties, or even new seedlings without further crossing, may result any year in producing a better plum than any hitherto pro- duced. Indeed, this is to be expected, for in a sense the work is only begun. Even by hastening the time of fruiting through grafting seedlings on small limbs in the way already detailed, it is impossible to test any given seedling as to its fruit possibilities in less than two or three years. So there are only twelve to fifteen generations at most between my first hybrids and the seedlings of the present year. It is not to be supposed that all the possibilities of the multiple ancestry will be realized in any given individual within that comparatively short number of generations. So, notwithstanding the notable results of the experiments up to the present, I have every ex- pectation that the real greatness of my plum colony is yet to be revealed. Meantime it is gratifying to record that unprejudiced witnesses in many parts of the world have declared the members of the quartette jus* [76] Co ft ft ft* <» ■»» r'ff'^« & XS5 a 2 c ft £isa. 5 o "• 5. it • 3 s.~ 3 3« 3 H ft O ft • -» ^ -ft 3 ft" £.5 g a » § ft 1*5 "g ao ft i ft*^* ft ifs§i a ""-is 8§SS€s s&j 2 =S "ft ft &. 2,<* 2 -~ p S o i •» t-w _ "a 2 S » g 5-' 7 % 5 «■ 2 ~ 3 »£ 3 5 3 52 o S S*§8| " "O » g H ~ e a -*.»-2.n' a. - !-«o> 3 c !~ s§ ft ft 5 re 7" 0"o ft § H o o " 3 *• - 2 ft r» K F»6*g St » ™ 3 f?a a" * Ik a~.S: s •» r 3 re q * 3 5 £3b. ■^t) a «; a.i: 3 b-S -•« £. •» B" i B" re B 3 a- » ft ? o*a a *> so a LUTHER BURBANK until man undertook the education of the fruit and trained it for that particular purpose. Remote Sugar-Producing Ancestors Nevertheless all that we know of heredity suggests that the effort on the part of man to develop such a trait as this would not have been successful had it not chanced that there were among the ancestors of the prune some races that possessed a tendency toward the peculiar prop- erty of producing very sweet fruit. There is noth- ing anomalous in that supposition, however, for it is well known that many tropical fruits tend to have a high sugar content. Such is the case, for example, with the date, the fig, and the pineapple. The orange, also, in some of its varieties, is a very sweet fruit, and there are numerous others among the fruits still confined to the tropics that show the same quality. Indeed, in general it may be said that fruits growing in the tropics tend to have a high sugar content, the reason being, perhaps, that in hot climates this is necessary to insure preservation of the fruit long enough to permit it to serve its purpose in protecting the seed during its growth and preparation for germination. But as fruits migrate to temperate zones, they tend to give up this habit of sugar production. All [86] ' o Q c LUTHER BURBANK pulpy fruits, to be sure, develop a certain amount of sugar, but the percentage is relatively small with most fruits of temperate climates. The con- trast in this regard between the average wild plum and such a fruit as the fig or the date is very striking. But we have seen illustrated over and over that a habit once ingrained in a race is with very great difficulty shaken off altogether, so it is not strange that, under exceptional circumstances or condi- tions of soil and climate, an individual plum tree might show reversion to the state of its tropical ancestor and produce a fruit much sweeter than other plums. Such an individual, if its fruit came to the attention of the orchardist, would be likely to be preserved and propagated; and in the course of time, through selection among the seedlings of this tree, a race of sweet plums would be developed. But it is only under conditions of artificial cultivation, in all probability, that such a race could be preserved. For, of course, the production of a large amount of sugar must draw on the energies of the tree, and if this increased sweetness of fruit did not prove beneficial to the tree itself, natural selection would presently weed it out. So, as I said, we may fairly assume that it is [88] The Giant Prune on the Branch The fruits of the Giant are so placed on the tree that it will bear an immense load without breaking. The heavy fruits are borne on the strong wood near together, but far enough apart to obtain a good distribution of weight. This plum is now grown extensively in Australia and New Zealand, as well as in many other countries. LUTHER BURBANK only within the comparatively recent period since the plum was under cultivation that the develop- ment of a race of sweet plums, which we now term prunes, has taken place. Just the Right Skin-Texture As to the other characteristic prune trait, that of developing a skin of such texture that it will crack in precisely the right way when put into the alkali bath, this may fairly be assumed to be an even more recent acquisition. Yet here, again, we may assume that there were ancestors of the plum that developed character- istics of skin of which this is a reminiscence. And it is not very difficult to conceive how this may have come about. The wild plum quite commonly grows along the water courses and by lakesides. It may chance that plums growing along the shores of the Medit- erranean, or perhaps by some inland body of salt water like the Dead Sea, were covered on occasion with salt spray from dashing waves or saturated with the brine when they fell to the earth. In such case, varieties that chanced to endure this treatment best would be the ones preserved, and in due course a race of plums having the right texture of skin to stand this treatment would be developed. This particular quality of skin would doubtless [90] ON THE PRUNE be subordinated when the plant migrated to regions away from the salt water and hybridized with other races. But here as before the latent trait would be preserved as a submersed factor in the germ plasm, ready when the occasion arose to make itself again manifest. But how, it may not unnaturally be inquired, would man himself discover the value of the alkali bath in preserving the prune? Granted that a prune had been evolved through artificial selection that had a sufficiently high sugar content to make it a drying prune, how chanced anyone to hit upon the particular method of dry- ing that is now employed, an essential preliminary of which is the submersion of the fruit in the alkali bath? The question is doubly pertinent because even to this day in France the use of this method is by no means universal. In many cases the prune is still dried with the aid of artificial heat, the fumes and smoke of wood or charcoal taking the place of the alkali bath in giving the right quality to the skin and aiding in preservation. So we may assume that the simpler method of using an alkali bath is of very recent origin. Not unlikely the discovery was made altogether by accident. Many of us can recall that in our boyhood days [91] LUTHER BURBANK it was customary in New England to make lye for use in the manufacture of soft soap by perco- lating water through barrels filled with wood ashes. The lye thus made is closely similar in composition to the fluid that is now used in pre- paring the prune. It seems a reasonable conjec- ture that the discovery of its value in this connec- tion may have resulted from observation that plums which chanced to drop into a bucket of lye, when removed and thrown aside were more resistant to decay than other plums. Such a chance observation would have sufficed to give the clue to some ingenious person, and the value of lye as an aid in making the plum into a dried fruit would thus come to be understood. But whether or not this was the manner of dis- covery, the fact remains that the lye bath is an essential part of the process of curing the prune. Therefore the quality of skin that adapts the fruit to respond properly to this treatment is one of the absolute essentials that the fruit developer must have constantly in mind. How Sugar and Lye Co-operate It may seem rather curious at first glance that a high sugar content should be essential to the preservation of the prune, when we reflect that sugar is a very fermentable substance. Everyone knows, for example, that starch is transformed [92] ON THE PRUNE into a form of sugar before it is fermented in the manufacture of alcohol. How, then, does the sugar in the prune prevent the fermentation of the fruit and insure its preservation? The answer is that sugar ferments only under influence of certain living micro-organisms, and that these micro-organisms cannot work in a too concentrated solution of sugar. There are myriads of the microbes spread broadcast everywhere on the wind, and of course they find lodgment on the skin of the prune as on every other exposed surface. But the alkali bath to which the prune is subjected, destroys these germs at the same time that it cracks the skin of the fruit. Other germs would find lodgment, however, and set up fermentation, were it not that the cracked skin permits a very rapid evaporation of the water content of the fruit. This quickly brings the sugar content to a degree of concentration that makes it a powerful antiseptic — that is to say a germicide that destroys any micro-organisms that enter it. But unless the prune has at least 15 per cent of sugar in its pulp, it will take too long to desiccate it sufficiently to give the sugar the right degree of concentration. And unless the conditions are very exceptional, even when the plum has a sugar con- [93] LUTHER BURBANK tent of more than 20 per cent., it still will not dry rapidly enough to escape fermentation unless its skin cracks in just the right way. A difference of the hundredth of an inch in the average interval between the cracks may make all the difference between a satisfactory prune and a nearly useless one. Of course in the pure dry air of many regions of California, under a cloudless sky, a very sweet prune will often dry perfectly without the aid of the alkali bath; but it would not do for the prune raiser to depend upon these conditions as a gen- eral thing. He must control his prune, for he cannot control the weather. Difficulties in Schooling the Prune It is obvious, then, that the plant developer must always bear in mind the two particular features of the fruit's education he has to contend with. But it is also understood that there are many other features that cannot be ignored. A prune tree, like any other plum tree, must be a good grower and a full annual yielder. The fruit must ripen early in the season while the days are long and warm. It must drop from the tree in exactly the right stage of ripeness that the or- chardist may not be put to the trouble and expense of picking it. The fruit should have a small stone [94] Prunes Drying on the Tree A plum that has a sugar content sufficiently high to cause it to dry without decaying is legitimately called a prune. The one here shown appears to have that characteristic. But there is an- other quality which a good commercial prune must have— it must drop from the tree when ripe. So the clinging propensity of the prunes here shown is a fault that bars this particular variety from popularity. LUTHER BURBANK and if possible a free stone — overlooking for the moment the question of entire stonelessness which will doubtless be required of the prune of the future. Again, the trade demands a glossy black prune, for — owing, perhaps, to the fact that the French prunes, especially those cured in the smoke, are black — the average purchaser is prejudiced against the prune of lighter color even though it be of better quality. When we consider how many of these traits are different from those required in the ordinary plum, and hence have been developed in recent times under conditions of artificial selection, it will be obvious how largely the task of the prune de- veloper must be carried out in opposition to the main stream of heredity; and it will not seem strange that forty years has proved none too long a time in which to develop the perfect prune. If I were to attempt to make a guess — it, of course, would be only that — as to the number of generations that have elapsed in the history of the prune since the qualities that chiefly characterize it were developed, my estimate would be some- thing like this: The tendency of the fruit to drop promptly at the right time has been in vogue for perhaps only five or ten generations out of the thousands of [96] ON THE PRUNE generations since plums were brought under cultivation. The quality of producing sufficient sugar in the right form for drying may have been developed during perhaps the last twenty-five generations; but it has been brought to its present high percent- age during the most recent half dozen generations. The condition of the skin which allows it to crack in just the right way has without doubt been cultivated for only a few generations. But on the other hand the fairly edible flesh, not having a high sugar content, has been the heri- tage of the plum for thousands of generations. So we can readily understand that the plant developer may secure among many thousands of seedlings, nearly all of them producing plums of fair quality, perhaps only one or two that show the qualities that specifically characterize the prune even in a minimum degree. The progenitors of the seedlings may have been prunes of fair quality; but the seedlings themselves have gone back to the blanket stage of plum development. The chances against securing even a single fruit that combines all the desired qualities among any given lot of seedlings are so small as to be almost disheartening. Indeed when the plant developer brings [97] LUTHER BURBANK together two strains, each carrying its galaxies of more or less antagonistic characters, it is not altogether unlike scattering the letters of the alphabet in a whirlwind and expecting them to fall together in some chance eddy in such a way as to spell out some specified word. Marking Progress I was not unmindful of the difficulties of the project, but nevertheless the obvious need of a better prune than California growers had been able to secure by importation appealed to me from the time of my first coming to the state; and when I undertook plant experimentation on a large scale, the development of the prune was one of the things that first engaged my attention. This work began about 1885, when I was grow- ing seedlings of the European plum, Prunus do- mestica, from which practically all the prunes have been developed. I have told in an earlier chapter of the success that ultimately attained the effort, through the development of the sugar prune. Here I wish to tell a little more at length of some of the tentative efforts and partial successes that paved the way for the final realization of an ideal. As already told, I began experiments by hy- bridizing the French prune with the larger and handsomer but less sugary variety known as [98] \ vAv.v.v;j ■ iff* , ' A^%' \ § Prune Tree in Blossom A prolific bearing prune tree in blossoming time is almost a solid mass of flowers. The virility thus evidenced is a very desirable trait as it insures a full yield of fruit; but it is obvious that a tree that produces fruit in such superabundance will require attention in the way of thinning the fruit if the individual plums are to attain a reasonable size. LUTHER BURBANK Pond's seedling, and in California often called the Hungarian prune. The little French prune was selected as the parent tree and many thousands of blossoms were pollenated from the Hungarian. This was in 1885. Four years later, at the meeting of the Califor- nia State Horticultural Society, I had the pleasure of exhibiting fruit of seventy different varieties of these crossbreed seedlings. During the next winter a purchaser of the commercial part of my nurseries, being ignorant of the value of these crossbreed prunes, destroyed sixty or more of them. Fortunately, however, cions from several of the most promising had been grafted on older trees. Among these selected grafts were two that gave much promise. These were advertised in New Creations of 1893. The Giant Prune In 1895 one of the new prunes was introduced as the Giant. It was so well received that four years later it was placed on the lists of fruits recognized by the American Pomological Society. The Giant is a well balanced cross between its two parents the French prune (d'Agen) and the Hungarian. Fruits average 1% to 2 ounces each and are of a sweeter and finer texture than the Hungarian but not so firm and sugary as the prune [100] Thinning a Prune Tree In Mr. Burbank's orchards the superabundant fruit on the prune tree is shaken off by lightly tapping the branches with a piece of rubber hose adjusted on the end of a fish pole. This treatment does not injure the tree, and is particularly valuable for first thinning. It may be desirable subsequently to thin further by hand. LUTHER BURBANK d'Agen. The large size, handsome appearance and rare keeping qualities place this among the best canning, shipping, and market fruits; but, unfortunately, the Giant follows its pollen parent the Hungarian in having a low percentage of sugar; so it does not cure well as a prune. Here, then is a specific illustration of the ten- dency to revert to the characteristics of the plum and to give up the special qualities of the prune. The Giant is a valuable fruit, excellent for shipping and especially good for canning. When placed in boiling water the skin immediately rolls away from the fruit, leaving the rich honey-col- ored flesh ready for the can. The plum has made its way to distant terri- tories, and is now grown extensively in Australia and New Zealand, being especially prized for canning purposes. In California it has proved a favorite and it is greatly superior to its staminate parent the Hun- garian prune, especially for shipment. But it is sold as a plum and not as a prune. The Pearl Prune Obviously, then, this was not the fruit I was seeking. But my experiments continued and after a few more generations of crossing and selection, I found among the seedlings one that produced a fruit in many respects more promising. [102] ON THE PRUNE This fruit was introduced in 1898 under the name of the Pearl prune. The Pearl prune originated as a seedling from the French prune. It is usually a little larger than its parent, but somewhat more flattened in form. The skin and flesh are pale amber and so translu- cent when ripe that the stone can be seen through them. It is really a delightful prune, of exceeding high flavor, delicious aroma, and melting flesh, sur- passing even the true Green Gage plum. No prune excels it for attractive fragrance. When cured it produces one of the most delicious of prunes; but it requires care in handling, since it does not cure well in the open air. Its chief fault is that it is not very productive, although healthy and vigorous. It was sold to a New Zealand firm for intro- duction in the Southern Hemisphere in 1898. I myself introduced it in the Northern Hemisphere. The New Zealand nursery company recom- mends it for that country in a recent catalog as follows : "Pearl :— Raised by Luther Burbank. A seed- ling of the well-known French prune, which it surpasses in size of fruit. It is very handsome, flattened ovoid in form, white, semi-transparent, with a heavy bloom. In honeyed sweetness, com- [103] A Typical Prune Cluster Before Thinning It is obvious that there are more prunes here than can attain good size without injury to one another. Hence the necessity of thinning, one method of accomplishing which is shown in the preceding plates. Prune Cluster After First Thinning This is the same cluster of prunes shown in the pre- ceding picture, after the cluster has been partially thinned by tapping with the rubber hose. The second, or hand thinning, will take place in a week or so, at which time one-third to one- half of the prunes here shown will be removed. LUTHER BURBANK bined with a peculiarly attractive fragrance and flavor it excels all other prunes or plums. It requires care in handling, and will not cure well in the open air. It is especially recommended for market and home use when fresh." The following quotation from "The Plums of New York," written in 1910, shows how this vari- ety was regarded in New York at that time: "The variety now under notice is one to be pleased with if it came as a chance out of thou- sands; its rich, golden color, large size, fine form, melting flesh, and sweet, luscious flavor place it among the best dessert plums. In the mind of the writer and of those who have assisted in describ- ing the varieties for 'The Plums of New York,' it is unsurpassed in quality by any other plum. The tree-characters, however, do not correspond in desirability with those of the fruits. The trees, while of medium size, and seemingly as vigorous and healthy as any, are unproductive here. In none of the several years they have been fruiting at this Station have they borne a large crop. If elsewhere this defect does not show, the variety becomes at once one of great value. "The fruits of Pearl are said to cure into delicious prunes — to be readily believed by one who has eaten the fresh fruits. This variety ought to be very generally tried by commercial plum- [106] ON THE PRUNE growers and is recommended to all who grow fruit for pleasure." Other Partial Successes Another prune that I developed somewhat earlier was named the Honey prune. This was one of my earlier seedlings and not a hybrid. It was of better quality and handsomer than the Green Gage, the standard of excellence at that time. The tree was not remarkably pro- ductive, but the variety has been welcomed as a home fruit in several localities of California. It was not considered worthy of general introduction but a few trees were sold to local growers who were interested in this variety and felt that it met the demands of their locality. A seedling of the prune d'Agen which I called Miller, was sold to Leonard Coates of Morgan Hill California, in November, 1898. This he introduced in 1908 as the "Improved French Prune." Later the name was changed to "Morganhill." The introduction of this prune as described by Mr. Coates himself furnishes an illustration of the length of time it usually takes for the public to become accustomed to a new fruit. In a letter Mr. Coates says: "We did not attempt a system of advertising in the start but rather tested it thoroughly for some ten years or so. It is very hard to introduce any [107] % ■ lawiiift jpi 1 — til ' i : 1 s I j Si^ •S Q c: 3 ft. V OS J. 4, I •** 5 ft. ,.2-B eta*: — ss e 0 a •- SJ £ ^^ » B ° a oS . Ej *! »- w i i £ 3 O C5 b := as fcSv.2 w w 3 c ' O a ». >-. a, t! £ n. . - C _B .-- ^ .o 3 _ 3> fc. «, "B "- ~ 5 s °> c-b 3 B. •~ o I, ON THE PRUNE new fruit as so many have been put on the market without real merits. Fruit growers, however, appreciate to a considerable extent, the value of selecting good varieties of fruit to propagate from. It seems that the chief introduction of pedigreed stock has taken place since our present nurseries were located and advertised on letter heads, etc., as specializers in pedigreed stock. "The Miller prune which we now call Morgan- hill has been coming under the head of pedigreed prunes. We called it in the first description 'Im- proved French.' Very few people had enterprise to buy these trees at any increased figure and now we are propagating them at the same price as any kind of prune tree. About half the people seem to ask for pedigreed prunes and the others simply say 'French prunes.' " This, then, suggests a measure of success. It constituted at least a good beginning. Successes more unqualified were to follow; but the work just described was instrumental in lay- ing the foundation for the later improvements — improvements that culminated in four prunes, one of which is already revolutionizing an entire in- dustry, while the others have intrinsic values at least as great. An account of these perfected prunes will be given in the succeeding chapter. [109] «•*•=:- ai^-2^S«« fe I § ^ ft, to is!* : <" «j S a-- 5 r h *> °-sl i§|, •" 5 "> (5. ° <5 •9 U I- V « •i c.c g o *£ 5 ... <» ft ■5**9 <=> 5i © © a <*> ~ s *»£ «^£ ~ ^3 Pi >~ « t, j> £ *> e s, c cats.:? •C •> 4> 3 « B ss.Sior ■SsfcS- ; Z* *~ ft a «> S < g«~ Four Burbank Prunes, and The Work Behind Them Revolutionizing an Entire Industry A BRIEF outline of the story of the sugar prune was given in a chapter of an earlier volume. The preceding chapter gives further details of the quest of a perfect prune. In the present chapter I wish to speak more of results than of methods, and to present somewhat in detail the characteristics and merits of the four nearly perfect prunes that have been produced as the result of my long quest. While some of the details here presented appeal rather to the orchardist than to the general reader, yet the story as a whole will be found not without popular interest. The fact that the growing of prunes is an industry of great significance, and that the fruit is everywhere an important commer- cial product would furnish ample excuse, were excuse needed, for entering somewhat more into [Volume V — Chapter IV] LUTHER BURBANK detail as regards the specific qualities of my quar- tet of prunes than has been done in the case of most other of my plant developments. The "Splendor" Prune Another prune of the same parentage with the Giant (referred to in the preceding chapter), namely, the Hungarian prune, crossed with prune d'Agen, was advertised at the same time, under the number "A. P. 318" in New Creations of 1893. This was purchased by Stark Brothers of Louis- iana, Missouri, who procured the entire stock for $3,000, and named it "Splendor." This prune is very much larger than the com- mon French prune, is oblong, has a rich violet- purple skin, and the flesh is exceedingly sweet, and black when cured — a great advantage. The American people have been educated to black prunes and generally prefer them to those of lighter colors, following the fashion set by the French smoke-dried prunes. The Splendor fully answers the desire on the part of the buyer and consumer for a "black" prune, of large size and superior quality. Splendor prunes, when cooked, require little sugar, containing about five per cent, more sugar than the French prune, its quality and flavor are superior, and it has a perfectly free stone smaller than is usual with prunes. [112] A • ■It . -J&l- *cJ #- *•', I v "Y -/ W a Splendor Prune Graft in Blossom This picture not only shows the admirable quality of stem of the Splendor prune, and its even distribution of blossoms, but it gives a good idea of a typical Burbank graft* LUTHER BURBANK It ripens here two weeks earlier than the French prune. The tree is even more productive, it is a more constant bearer, and is sturdier than its French parent. The tree is a well proportioned one, re- quiring but little pruning. The fruit is borne in clusters commencing low down on the body of the tree. Many thought that this excellent prune would soon completely displace the prune d'Agen. Sure- ly if quality and productiveness were all that were demanded by the grower, this would have occurred. But Splendor has one peculiarity which places it at a serious disadvantage for general commer- cial purposes as a drying prune: the fruit clings to the tree when ripe, where it gradually dries into a delicious, sweet prune. As prune growers like to have the prune fall as soon as ripe, to save trouble in harvesting, the clinging of the Splendor to the tree is considered a more or less serious fault. However, it is quite commonly planted wherever the German prune thrives, and gives excellent satisfaction, except for the extra trouble of picking. It is shipped East as a fresh plum from sections of California in large quantities and is unusually well adapted to shipping, on account of its large [114] ON THE FOUR BEST PRUNES content of sugar, making a fruit which carries well. The Sugar Prune The Splendor was the best prune I had hereto- fore produced, but it clearly left much to be desired. It was with intense satisfaction that I was able to offer, in New Creations of 1899, a prune that at least approached the realization of my ideal. This was another seedling of Petite d'Agen. It was christened the Sugar prune. For fourteen years I had labored to produce a large, early, productive, handsome, easily cured, richly flavored prune with a high percentage of sugar. The prize appeared in 1893, and by 1899 I had tested it sufficiently to warrant its introduc- tion. Numerous growers had ordered $50 to $500 worth of wood for grafting — regardless of the quantity — even before grafting wood was offered. I had worked diligently and unceasingly, watching for the slightest indication of variation in the direction desired. Finally through syste- matic crossing and careful selection, my cherished desires were realized — after years of persevering effort and patient waiting — in the Sugar prune. In this, at last, I found a prune possessing the best qualities of all the prunes combined in one; and several of these qualities were intensified. [115] LUTHER BURBANK The Sugar prune had no rival until the advent of the still newer prune, the Standard, which I introduced in 1910. When the selection of seedlings was made from which the Sugar prune originated, about one-half were at once discarded. Only those were saved which had the customary indications of good fruiting — large leaves, prominent buds, and strong, heavy wood with short joints. Grafts from the young seedlings were placed upon Japanese plum stocks. This was done be- cause there was no other stock at hand at that time. It proved to be a costly experiment, because more than half of these new, promising seedlings died before bearing fruit. Some of the grafts did not start at all; some made a short growth and died the first season; some grew a few seasons and died. Fortunately, however, some thrived as well as on their own roots. The grafts that bore the first fruits of the prune which was later named "Sugar," made a fair but not a good union with the Japan plum. Although the first fruits of this variety were born on Japan- ese plum stock it is not recommended that Sugar prunes be grafted upon such stock. Roots of the Myrobolan plum make better stocks. Almond roots are also highly commended by some or- chardists. [116] ^5g o <» £ S3 J ~ B 3" re K.2- a EL-53, a^5 a. S a. , :* a, ft * -a 3 * 2. "2. &• •oss a ft - t~ J» (ft "1 ►. „. "••a = n ~,q re ;--~2 ft. a "> ' a "" ~a K ■a -a S"^55 a. ft-«: S- ra ***i5 t? ^ ft 5 LUTHER BURBANK properly, so that the result is a big, quickly-dried prune of superlative quality. The following comparison of the French and Standard prunes, made by G. E. Colby of the University of California, gives a good idea of the value of the Standard prune: Average The "Standard" French Prune Average weight in grams. 49.7 23.6 Number per pound 9.1 19.1 Flesh, per cent 96.5 94.2 Pit, per cent 3.5 5.8 Sugar, per cent 18.9 18.5 In case any one wishes to change a prune orchard over to a more profitable variety, whether for drying or shipping fresh, I would strongly recommend the Standard for grafting. The Standard was offered to orchardists in my catalog of 1911-12. The trees were sold at $3 each, and thousands of trees have been distributed, but it will be a good many years before the real value of this superior prune is fully appreciated. Clingstone versus Freestone The most striking individual peculiarity of the Standard prune is its freestone quality, already referred to. The development of this character is of such interest and importance that it calls for more than passing mention. [126] ON THE FOUR BEST PRUNES At first, it is very probable, all fruits were cling- stones. The stone was probably firmly attached to the flesh from the time of the forming of the meat to the final decay of the fruit. The stone in fruit acts as a support to the flesh, to which it is attached and around which it grows. The clingstone feature was evidently an advantage to the fruit, as plum and prune seeds will not germinate if thoroughly dried, and the clinging meat in most of the fruits keeps the seed moist for a longer time, thus helping to conserve its vitality until the proper season for germination. Where the flesh is attached to the pit, the circulation between the pit and the surrounding flesh is less interrupted, probably an advantage to the development of both. The clingstone is thus the more normal condi- tion of fruits. Most fruits are clingstone until brought under cultivation. All fruits, both wild and cultivated, are clingstone until towards the time the ripening process commences. That many cultivated fruits are freestone is no doubt the result of artificial selection to meet a very natural demand. Nuts furnish analogies that help us to under- stand the relations of seed-stone and fruit. The case of the almond, which was perhaps more nearly the parent form of stone fruits, is particu- [127] LUTHER BURBANK larly instructive. In place of the rich surrounding meat which we see in peaches, apricots, and plums, the almond has a leathery skin, which is inedible. This generally clings to the stone persistently in the wilder forms, but with the best cultivated almonds the nut drops readily from the husk or outside covering. Similar to the persistency with which the flesh of the plum clings to the stone is the attachment of the husk in the walnuts and the chestnut, in each of which the husk separates with more difficulty in the wild than in the best cultivated varieties. From the standpoint of protection and repro- duction of the almond, the clinging husk is an advantage rather than an objection. The seed of the almond will germinate after being thoroughly dried. It needs no flesh to tide it over, as do the pulpy stone fruits. But for men's use the clinging husk is a disadvantage, and the clingstone habit has been eliminated in all the best cultivated varieties of the almond. In the plum a similar change has been devel- oped by selection. The meat does not cling to the stone, in many cultivated varieties. In the almond the quality of the meat has been greatly improved, while the husk or immediate covering has not been improved in any respect, as no use is made of it. [128] The First Stoneless Prune The reader is familiar with Mr. Burbank's wonderful experiments in producing stoneless plums by breeding from partially stoneless French plum. In the same way attempts were made to produce a stoneless prune. The specimens here shown were the first that attained partial success. These prunes were stoneless, but were deficient in size and other qualities, and further experiments were nec- essary before a really valuable com- mercial stoneless prune was developed. LUTHER BURBANK Even a freestone fruit does not start as a freestone, but the flesh tends to leave the stone as the fruit approaches maturity, very much as a leaf ripens away from its supporting stem in the fall when it has performed its annual function, or the fruit parts from the tree when it is fully ripe. The flesh parts from the stone by a natural process. This leaves the stone either "free" or partially free. Some individual trees, among a lot of seedlings — chestnuts in particular — will hold their leaves persistently all winter (this persistence is espe- cially common with crossbred chestnuts) even when thoroughly dead and dried, giving an untidy appearance to the tree, while the leaves of other seedlings fall at once and leave the branches clean and free. This is a similar process to the parting of the flesh from the pit in fruits, both being ripening processes. There is every gradation between the complete attachment we call "clingstone" and the "free- stone" condition. In some fruits there is a single point of attachment; in others the flesh adheres over a part of the surface while the remainder may be wholly free from the stone. There is also another form of partial separa- tion found in some fruits where the flesh clings tenaciously to the stone until fully ripe, when it 1130] a ft «§ tg*3> ?JS a n us a-o ?»>B O. a a* &• f^ o ** 9 2 ^■a a <* c o c a>^ re s. 2 r* a- re SSr§«Bft5 i. a-* S. o a ? c 2, a'?1 0.* 3a §a§ "5re -. a^ftSS^Sreto » ts a » ? i re ft. «s K B* § *§« a © ~ o " ft **IB |k> C w. Cft re a. to a a = £.re3 re g« 5. ft 2 2 ."a * re i r> Q a" 9 Lb itoft"c f " re g B ■ i*- re ~i re re ' ft?* to B rs rs Co LUTHER BURBANK parts readily, while in others it may separate from the fruit and be shaken about within it even before thoroughly ripe. There seem to be two forms of variation, one in the time of attachment and the other in the persistency of attachment. This persistency of attachment varies greatly; in some fruit it would be possible by a little work to cut around the stone and in others the flesh is attached so closely that to remove the stone satis- factorily you must have sharp tools and use them with discretion. The old hereditary tendencies make it difficult to change plum and prune heredity so that it will produce freestones instead of clingstones. Never- theless this has been accomplished with several varieties, including the Standard prune. Of late the canners have preferred the cling- stone peaches mostly, perhaps because they have a firmer flesh that does not fall to pieces when cooked, as the freestone peaches generally do. The pit is very easily removed with a sharp instrument made for the purpose. With this exception, fruits are generally more valuable when they are free- stone. The Conquest — A Stoneless Prune But what if the fruit had no stone at all? That would, indeed, be the ideal condition. And [132] S a«^» Sp »s 3o 5-Sf » ° " scoob' i m. _ a 1 a « ^. «• 1 » eoa ^i 3 8 S «• » ^* 3 *3 ft. Sr c* ►-4 «"-h n © tl 3 ft ►ft -J 3 OS <* 3 69 LUTHER BURBANK this ideal is met, or nearly met, in the fourth member of my quartet of best prunes — the Conquest This, the newest of my prunes, was first offered in the catalog of 1911-12. The work of producing the stoneless prune parallels that of the production of the stoneless plum, a preliminary account of which has already been given, and fuller details as to which will ap- pear in the succeeding chapter. Here it is neces- sary to mention only such aspects of the work as refer specifically to this prune. The Conquest was produced by crossing a par- tially stoneless plum in my orchard with the French prune. The difficulty of getting a stoneless prune was about equal to the difficulty of getting a satisfac- tory stoneless plum. If I had crossed with a plum it would have been a hundred times more difficult to get the prune characters than it was to get stonelessness. In the Conquest the size and quality of the French prune is retained, together with the stone- lessness of the other parent. This cross brought out both prunes and plums — some of the largest plums ever seen. At first they were all blue like the stoneless parent; later they took on all colors of ordinary plums. [134] a*" a 5 B ^) re «2 * ^ re 8 2 » «*■ K-o5 a" c ft E; re 3" ~ • tj re o re ?f «§5"s Sea* © ~. t-. a >?2 a* .»f r ~. to 5 Si 5:3*2 £a « 5. re ft a* re to a re 1 2 *• 2.2 S * 2 ~^§:°!£ £ «• ~a 2 §*S"2to*g a» <• „ « -2. m « a a i § O S3 S 3 TO TO e* LUTHER BURBANK least within the possibilities, as hinted in our dis- cussion of the peach, that the quality of stoneless- ness may be extended from the plums to the allied tribes of stone fruits by hybridization. Conceivably the descendants of the little bul- lace may include not only the races of cultivated plums but even all races of apricots and plumcots and cherries as well. But even though the view be confined to much narrower limits, it still remains true that the stoneless plum is among the most important of plant developments. So it may be worth while even at the risk of a certain amount of repetition to review the history of this development, and in particular to add a few details that have not hith- erto been presented. It will be recalled that the little sans noyau, despite its name, was not altogether stoneless, inasmuch as each fruit had a rim of stone more than half way around the kernel; also that the fruit itself was only about the size of the ordinary cranberry, and was harsh, acrid, and unpalatable. Yet when this unpromising fruit was crossed with the French prune, and with numerous other plums and prunes, some of the crossbred seed- lings produced fruit larger than the French prune, and nearly all of the hybrids were superior to the wild parent. [152] ~ 3 (» •a B 2 ~ §.§5:2 a.S*o • 5 °. a <» t a 3 f 3S- s a, 2 « ©8 * 2. CO 3 B 2.^5- °>s * a*! -» a ** <• C <*> n ^*« o K Co LUTHER BURBANK All the seeds of these hybrids were carefully saved and planted. The seedlings were grafted on older trees, and a few seasons later still better ones were obtained; plants bearing larger fruits and many of them showing the tendency to abandon the stone. The first generation hybrid seedlings of this type, which were quite numerous, had mostly the French prune for the pistillate parent. A good many, however, were from the reciprocal cross. Of the latter, the crooked thorny seedlings which indicated that they were not crossed, or had reverted to the wild type, were generally destroyed even if they bore stoneless fruit. Those which showed the French prune or ordinary plum type were grafted into older trees to bear. All the seedlings from the cross of the sans noyau pollen upon the French prune were grafted and fruited even though many of them exhibited the thorny, dwarf, ill-shape of the wild parent. After the first generation the seeds of all were mixed, as there seemed no object in keeping them separate. For two or three generations there were all sorts of trees, the greater tendency being towards the bullace, which, being a wild type, would naturally be expected to have its characters more thoroughly fixed. In the first generation some plums were ob- [154] Large and Luscious This stoneless plum has distinction among the number- less others that have appeared in recent years in Mr. Burbank's orchards. It has good size in addition to its other qualities, and ultimately it will probably make a name for itself in the market. LUTHER BURBANK tained fully twice as large as the fruit even of the cultivated parent. But most of these had stones, and were, moreover, soft, sour, undesirable fruits. All but a few of the more promising grafts were removed from the trees, and the experiment was continued with the selected ones. In the next generation there was some general improvement in the growth of the seedlings and the size and quality of the fruit. And in later generations the quality of the fruit rapidly im- proved— combined with stonelessness — until I obtained two or three fine plums and prunes. These were grafted extensively and seedlings raised and selected for still further improvement. Some of the earlier results of these experiments were exhibited at the Pan-American Exposition at Buffalo, New York, in 1901, and aroused much interest among fruit growers. None of these, however, was worthy of introduction as a commer- cial fruit. The plum called Miracle was the first of the stoneless plums to be introduced. This is borne on a rather slow-growing tree and has the size, flavor and appearance of a small Damson, being about an even balance between the French prune and the original sans noyau in most of its characters. Some years it is quite productive, but it is not an altogether dependable bearer. [156] ON THE STONELESS PLUMS AND PRUNES A representative of the Oregon Nursery Com- pany, on a visit to my Sebastopol grounds in 1903, was greatly pleased with this variety, and at once purchased it. It has been advertised and grown quite extensively. Its flesh is of such quality as to be chiefly valuable for the making of jam. At that time it was the best stoneless plum in existence. But its chief merit was that it was the forerunner of a race of stoneless plums and prunes which will in time be grown wherever these fruits are raised. The Stoneless Prune The next stoneless variety to be introduced was the prune named the Conquest, with which we have already made acquaintance. It will be re- called that this is one of the quartette of best prunes described in the preceding chapter. From three per cent, to six per cent, of the bulk of the French prune is stone. The specks of stone that remain in the Conquest do not constitute more than one-thousandth part of the fruit, which is thus edible practically without waste. The Conquest was offered in my catalog of 1911-12 with the following description: "There has been known for several hundred years a wild plum, an unproductive, thorny bush, which bore insignificant, acid, bitter, wild berry- like fruits with only half or two-thirds of a stone. [157] LUTHER BURBANK Years ago it was hunted up in Europe with the plan in view of producing really valuable stone- less plums and prunes. The labor and expense incurred in these experiments have been enor- mous, but among the many thousand varieties, one really good stoneless prune was produced and is here ottered for the first time in the history of this earth. "The tree is a vigorous, healthy, rapid grower and unusually productive. The fruit is very simi- lar to its civilized parent, the common French prune, in form, size, color and golden, sweet, rich flesh. The stone has been eliminated wholly with the exception of a tiny speck. The fruit is so very valuable and the tree so very productive that I have consented to introduce it this season. It ripens with the common French prune and is in all respects very much like it in size, quality and appearance." The French prune is nearly oval but Conquest is slightly more flattened in form, like some of the German prunes. Further Improvement in Prospect Among the later seedlings I found some very good fruits which have reverted to the stony type, one of them in particular being extremely large and of sweet, rich, superior quality. Thus, after several generations of plums with- [158] Striking Contrasts The picture shows a blue stoneless plum growing on the same tree with the Barnblood plum — the result, of course, of a grafting experiment, in which the Barnblood tree was the stock. Such anomalies are common enough in Mr. Burbank's orchard, but are always interesting. LUTHER BURBANK out stones, those having ordinary stones again appear. There are others, however, that retain the stoneless condition, and are of exceptional size. Every color of the plum now appears in these stoneless hybrids — white, pale yellow, orange, scarlet, crimson, violet, deep blue, almost black, striped, spotted, variegated, and mottled in every way imaginable. They ripen from the middle of June until Thanksgiving, and while some varieties are no larger than a cranberry, others are larger than any other plum now generally cultivated, except perhaps the Climax, the Wickson, and Kelsey. After a time, no doubt, varieties may be pro- duced with solid flesh throughout, as many seed- lings now have indications of such a condition. The best stoneless plum thus far produced has a strong tendency towards this condition. I am often asked how the present plum with stones and seed will be replaced by the stoneless variety. Will the ordinary varieties be supplanted within a few years? There is no probability of that. It will be a long time before our present orchards are re- placed by trees bearing stoneless fruit. Long years of selective breeding have been required to give the plum its good qualities. To hold to present [160] *3 ft""*"* bob ?. © -. r <» •» e -•■o'g *£. 3g- <= S. O 2 c 5 2 ■a ^~ 5 <» « <* i 8 3 15 " *> a 21 a ^ a 3 8*8 e S» r* 512 ?Sa- n o*a ^* a *• o a ft •— a "i c a S » a. CO O a 0» © a !■■♦. ft LUTHER BURBANK The change from stone to stoneless fruit will come about by imperceptible steps. The change will be so slow as hardly to be noticeable. Poorer varieties of all fruits are gradually replaced by the better; so gradually that the change is scarce- ly noticed. Odd forms are constantly coming up in nature — like the little, deformed bullace that was the parent of the new stoneless plums. Sometimes their inherent prospective value is recognized — oftener not. A hornless animal appeared as a sport or sudden variation in Argentina half a century or so ago. Possibly this freak may have appeared a hundred times before. But in this in- stance someone having imagination noticed the mutant and fostered it, and we now have hornless stock from that Argentine variation, not only of the original but of nearly all breeds. Among fruits, changes no less marked are con- stantly arising, and as time goes on these will be more and more recognized, and appreciated and used. As a greater knowledge of plant improve- ment is becoming disseminated, more pronounced changes for the better will be made — the elimina- tion of stones and seeds being one of the most important of the many improvements required. The appearance of the stoneless plum, not as a chance sport but as the product of an arduous [164] ON THE STONELESS PLUMS AND PRUNES series of hybridizing experiments, may be taken as a sure augury that the conception of an age of stoneless fruits is not illusory — however long its coming may be delayed. — Man cannot take the Indian and say to him: "Be civilized" and expect him in a generation to drop the tendencies that have become a part of him through centuries of inheritance. % rf - mm ■4- r *rf The Gee Whiz Plum in Bloom The plum to which the rather startling name, "Gee Whiz," has been given is a complex hybrid. Like many hybrids it shows great virility, illustrated by the habit of blooming and bearina to the very tips of the limbs. The distribution of blos- soms on the tree here shown is practically ideal. Planning an Ideal Plum or Prune The Requirements and How They May Be Met WHEN I was in the nursery business a man came to me on one occasion and wanted trees for his orchard. I showed him my stock, but it did not suit him. He wanted trees that grew six feet high before branching. I had nothing answering that descrip- tion, so he bought elsewhere. In a year or two his trees were sweeping the ground, quite as might have been expected. So the orchardist came to me to find out what he should do. Naturally I told him he should have com- menced right by getting trees of the right form at the outset. Now there was nothing for him to do but to cut his trees back to the right height, and let them start anew, thus losing two years of growth. He did not like this prescription, but he presently had to follow it. Of course his trees [Volume V — Chapter VI] LUTHER BURBANK were never as good as though they had been given the right start; but their new condition was an improvement on the old one. This misguided orchardist was simply acting on the mistaken idea that was everywhere current until quite recently — the idea that it is necessary to run a tree into the sky so that other crops can be raised under it, and that teams can be driven close to the trees in cultivating. Nowadays the orchardist adapts the implements of cultivation to the tree, instead of adapting the tree to the implements. Or, what is better, he adapts the trees to the land and makes the orchard pay better and with less labor, without attempting to raise any other crops in the orchard. It has been discovered that skyscrapers in the orchard do not pay. A tree should be of such form that the fruit may be picked conveniently. It should not be necessary to use step-ladders to gather the fruit from the lower branches. In the case of the prune, in particular, a low- branching tree is especially to be desired, that the prunes may not get bruised in falling for even as tough a fruit as a prune may be injured in falling from a tall tree. Planning the Plum Orchard The old way of planning an orchard was to [168] ON THE IDEAL PLUM look over a catalog and order half a dozen of this or half a dozen of that, without asking any ques- tions or gaining information as to whether the varieties selected were adapted to the region where they were to be grown. And the old way for the grower or nursery man was to accept the form of the tree as it tended to grow, with little or no attempt to change it. But the new way is for the intending orchardist to select his varieties with the utmost care, paying careful heed to questions of soil and climate, and introducing only such fruits as are adapted to the conditions that must be met. And as to the trees themselves, when they begin to grow, the modern plant improver is by no means content to leave everything to Nature. He takes a hand from the outset, and largely determines the form of the tree. Moreover, the up-to-date orchardist will look beyond the existing variety, and recognize that it requires both imagination and labor to produce the ideal tree. Building an ideal plant of any kind is like building a house. Each must be planned in accord- ance with a clearly conceived idea. But there is this great difference : In the case of the plant you must wait for Nature to supply you with the material with which to build. [169] LUTHER BURBANK Plant building is architecture — but architecture with limitations. It is always slow and very often it is extremely disappointing, yet it has its encour- aging surprises as well. Times without number I have been ready to give up an attempt to secure an improvement on which I had worked unsuc- cessfully for years, when, just as my patience was at the breaking point, Nature would seem to have a generous mood and, as it were, throw the desired characteristic into my lap. What the blue print means to the architect, the conception of the tree or fruit or flower wanted should mean to the plant improver. It represents a precise ideal toward which to work, and it gives standards of comparison by which progress may be checked as the work progresses. In the case of the plum, it is possible to present the ideal to the mind with great accuracy. Of course it may not be possible to attain results strictly in accordance with the plan. But usually the ideal may be at least approximated if it has been intelligently conceived, and if it is persistently borne in mind. Specifications for an Ideal Plum Let us now note specifically and in sequence some of the practical points to be considered in planning our ideal plum. In so doing we shall find that there is a certain [170] An Ideal Plum Tree The modern fruit tree has been taught to assume a low rounded form, bearing its treasures within easy reach of the picker. In the tree here shown, the results of first thinning with the rubber hose are seen on the ground, and the second thinning is being performed by a boy who is able to reach most of the clusters without the aid of a stepladder. LUTHER BURBANK amount of overlapping, or perhaps we had best say interference, of qualities. A plum that is best for one purpose may not be best for another. We must bear in mind the different purposes to which a plum is put, and endeavor to make our plan comprehensive enough to cover all of them. There are certain qualities, to be sure, that are desirable in every variety of fruit. Large size, for example, and frost-resisting quality are seldom or never disadvantageous. Yet even this must be qualified, for, in case of a prune, drying becomes more difficult as the fruit enlarges, and unusual size may be a disadvantage. But for plums in general we aim at a tolerably definite combina- tion of qualities — size, form, color, flavor and hardiness — and endeavor to associate these in the same fruit. Taking up our ideal plum tree part by part, let us first consider the root. This is of great importance. A great difficulty of the French prune is that its root system is ordi- narily inadequate. It is usually necessary to graft this prune on other roots. Peach stock is some- times used to advantage both for this and for other varieties of plum. But there are some plums that do not graft kindly on the peach, and it is necessary in such cases to make a double graft, using first a cion of some plum that grafts well [172J Spur Bearing Clusters of seedling plums often grow close to the trunk of the tree, as in the case here shown. It is interesting to note that in this specimen the broad, healthy leaves indicate good fruit- bearing- capacity, and the beautiful clusters of plums show the justice of the prediction. LUTHER BURBANK on the peach, and then grafting on this the cion of the desired variety. This is obviously a rather tedious procedure. Fortunately it has been discovered that the Myro- bolan plum furnishes good roots on which almost all plums may be grafted, and this stock is becom- ing very popular. The roots of the apricot are also sometimes used successfully. On deep, dry soil, almond stock often gives the best results. But, of course, there will be great advantage if the plum can be made to grow a good set of roots of its own. It should be recalled that an abundance of roots is always closely correlated with abun- dance of foliage. One may tell at once in the orchard whether a tree has a good set of roots by observation of the foliage. And the close de- pendence of the roots on the foliage is a matter of common observation. Many orchardists fail to realize how completely the roots are governed by the amount of foliage. And even when this is realized the observed condi- tions are not always correctly interpreted. If the foliage did not govern the roots, our orchard trees would be of all sizes and of all degrees of vigor, whereas now, when grafted on seedlings of varying degrees of vigor, the trees are uniform. As to the stem of the tree, this should come up straight as a flag-staff, and should branch sturdily, [174] n a "~ S ? LUTHER BURBANK the branches coming out not quite at right angles but turning slightly upward. Branches should not turn down, nor should they be crooked. Moreover, the branches should not tend to grow too long and slender. Many seedlings tend to take on a bushy growth, which is undesirable. Others are too slender. Some have a general irregularity of growth, which is particularly objectionable. Brushiness invari- ably indicates a lack of production; it suggests a reversion to some inferior ancestral type. And it may fairly be predicted that the tree will show similar reversion as to fruit, producing a small fruit of poor quality. Brushiness is indicated by slender, too abun- dant, poor branches instead of sturdy branches. Slender branches can never be correlative with large fruit — they have not requisite strength. That is one of the many reasons why I select seedlings with large branches, and those having prominent buds and large, thick leaves. These are all indications of a bearer of large fruit. Large branches and large fruit are associated together through the effect of past heredity; just as, contrariwise, small fruit and small leaves and branches are the hereditary traits that are simi- larly associated with small fruit. Of course, it is not always possible, in the [176] A Practically Perfect Plum Tree This tree has perhaps been allowed to run up a little too high, and its branches have not been quite adequately thinned; yet on the whole it may be said to represent a practically perfect type of plum tree. Note the wide horizontal spread, bringing the main bulk of the fruit within reach of the picker when standing on the ground. LUTHER BURBANK present stage of orchard development, to secure a tree of perfect growth and form. This is true not alone of plums but of other orchard fruits. Some of our best varieties of or- chard trees, like the Bartlett pear, have branches too slender and upright, and do not carry the fruit well. The Bellflower, though a fine apple, makes a weeping growth. The Newtown pippin makes too slender and upright a growth. On the other hand, the Gravenstein apple makes a very fine, spreading tree, and the popularity of this variety may be to some extent associated with the almost perfect form of the tree itself. But it is one thing to observe that a tree is imperfect, and quite another thing to take the trouble to improve it. We know that the branch system should re- semble a vase in form, avoiding brushiness, wood- iness, or overgrowth. But many orchardists who are well aware of this will not take the trouble to prune the tree in such a way as to encourage this development; nor will they consider the matter of selecting a variety that tends to grow in the right way without pruning. As to the leaf system, it is always desirable that the foliage of a fruit tree should be large, thick and abundant. In the case of cherries it is particularly desir- [178] Ideal Foliage The foliage of the central tree indicates a vegetative and digestive system in first class condition. Such a tree, with its large, abundant foliage, may safely be selected for the production of a fine quality of fruit. As we have already seen, this selec- tion may be made when the seedling is still a small plant; the future tree will almost surely live up to expectations, based on its foliage. LUTHER BURBANK able that the leaves should hang over the fruit to protect it from the weather and from birds. With the plum this is not so necessary. Still the ques- tion of foliage should always be considered. Other things being equal, seedlings should be selected that show large, thick leaves. Blossoms and Fruiting It is almost axiomatic to say that plum seed- lings should bear perfect blossoms in reasonable abundance. The blossoms should be borne on the larger wood of the tree rather than on the tips, because the fruit is held better where it has the support of the older wood. Moreover, if the fruit is borne at the tips of the branches, these are brought too near the ground. The time of flowering should be given careful consideration in connection with the climate where your orchard is located. Many fruit trees bloom so early that in mild climates the late spring frosts injure them. In general, late-blossoming trees have an important advantage. It should be understood that a tree that blossoms late usually matures its fruit early, whereas one that blossoms early will usually bear late fruit. This is, of course, precisely the reverse of what might be expected, unless we bear in mind the reasons for the difference. A moment's re- [180] Protective Foliage Protection from birds and from the elements is a very important item with many fruits, notably the cherries, but in- cluding also many plums. This picture illustrates how vigorous foliage may give a large measure of protection to a clus- ter of plums. This picture was taken from above. Compare with the succeeding picture. LUTHER BURBANK flection makes it clear that late bearing and early fruiting should be correlative, being adaptations to a climate where the summer is brief. The bearing season of the plum may be short or long according to the use to which the fruit is to be put. Fruit that is to be gathered wholesale for the market should have a short season, the major part of it ripening at the same time. On the other hand, fruit for home use or a local market should have a long season. But even more important is the matter of "every year bearing." A tree that never makes a failure — one that bears annually and does not have any off years — is the kind of a tree that is needed. The orchardist naturally wants a tree that can be depended upon to give him a crop. A tree that sometimes balks after starting a lot of fruit, be- cause the temperature or conditions of moisture are not just to its liking, is not the kind of tree that endears itself to the fruit grower. It must be understood, however, that fullness of bearing has no necessary association with hardiness. The two qualities are quite distinct. A tree may have one quality and quite lack the other. It may be able to thrive under adverse conditions but not to bear under adverse conditions. The ideal tree, of course, is one that will not [182] Foliage Protection Further Illustrated This is the same cluster of plums shown in the preceding picture, but in this case the camera was adjusted below. Here are three plums that were totally invisible from above, and two that were only partially visible. The value of such protection from sun and elements is obvious. LUTHER BURBANK only thrive but will invariably produce a fair crop of fruit whether the season is hot or cold, dry or rainy. A fine practical test of fullness of bearing is supplied when a frost comes just after the blos- soms have dropped, while the miniature fruit is fully exposed. A tree that will stand this test may generally be depended on as an every-year bearer. Nowadays the plant developer has this matter of every-year bearing in mind, and varieties of plums have been developed which conform to this business principle. Our fathers pretty generally supposed that a fruit failure about every second or third season was to be expected. Now we know that the right variety of fruit can be depended on to give a crop each season. In selecting stock for your prospective plum orchard, bear this point very carefully in mind, and choose only such varieties as have the in- herent tendency to bear fruit with regularity. Size and Quality of Fruit It was just noted that a prune may be so large that it dries badly. This is not likely to be the case, however, if the prune ripens early and has a high sugar content. And as to plums in general, large size is, of course, a foremost merit. There are other fruits that sometimes tend to grow too large. This is true of certain pears; also [184] ^9BBHK9B a a 2.0.3 S i c » c « - a *> . °<~- §.3 3 sag o -sa S S So a * © i o3r 2 2. 2 a » ~S§ 2 * o a' 2 H Co "1 ~ <» "^ £§£««* Co 3 A 3 5 - o ~ 5 a- r* ■ «j =>■ 5' o •§Sg — 1 -T ^3 O Hi © 5" <3" 3^ __ * LUTHER BURBANK of some peaches. But the plum has not as yet been developed to anything like the maximum size, notwithstanding the very great improvement of recent years. A good many of my newer plums are giants in comparison with the standard plums of a generation ago. But no one complains that they are too large. On the contrary, their high price in the market is due in considerable measure to their large size. In selecting the ideal plum there is no reason nowadays why you should not secure one that bears fruit that is at least two inches in diameter on the average. In form the plum should approach the globu- lar. This is best in most fruits, for the reason that the spherical form is the most compact, and there- fore the one best adapted to handling and packing. The suture in the plum is a mark of recogni- tion, but of no value to the fruit in any way. It is mostly due to the fact that one side of the plum grows slightly larger than the other. But this is a matter that concerns the pomologist rather than the fruit originator or grower. The same is true of the ridge on the plum stone. It is a mark often used as a distinguishing character between different varieties, but which has no practical significance. The plum should be of some attractive color, [186] Progressive Ripening This cluster of Giant Maritima plums has one fruit nearly ripe, one nearly green, and two in intermediate stages. Suah uneven ripening is a fault in a shipping fruit, but it may be a merit in a fruit for home consumption, greatly lengthening the fruit season. LUTHER BURBANK red, yellow, or even a brilliant white. Green fruit is never attractive. It would appear that the birds and man have combined forces to produce red and yellow fruits by selection, because these colors are enticing, and we have come to associate them with superior qualities of fruit. The skin of the plum should be thick and firm, especially if the fruit is to be shipped to a distant market. For home use or a nearby market a thin- skinned plum may be quite as satisfactory. The bloom of the plum adds to its appearance, and its condition may be a test of freshness. The bloom evidently had originally a protective func- tion, possibly shielding the fruit from the sun, or otherwise protecting the juices from too rapid chemical change. The bloom may be developed on a fruit by means of selection where it is especially desired for any reason. It is obviously only a minor char- acteristic of the perfect plum. The flesh of the plum should be firm, particu- larly if the fruit is to be used for shipping pur- poses. The texture may be shown by cutting the fruit with a dull knife. For home consumption, plums that are very watery are often considered a great treat. I have some splendid watery plums now growing — fruits that almost melt in the hand. [188] Ideal Form and Bloom This is Mr. Burbank's famous Combination plum, a fruit so named because of ihe large number of divergent ancestral strains that are represented in its heritage. These plums have an almost ideal globular form, with a thick bloom evenly distrib- uted, so that it affords protection to the fruit everywhere. LUTHER BURBANK But these have not the texture to stand the trip to market and keep in good condition. The orchardist must bear this difference clearly in mind, and let the choice be determined by the use for which the fruit is intended. Nearly white is usually the most suitable color for the flesh of the fruit. Yellow flesh is also ad- missible, and sometimes pink or crimson. The plums with crimson flesh, as we have elsewhere learned, are all descendants from the Satsuma plum which was one of my earliest importations from Japan. Plums show almost every possible combination of flavors. Appearances are sometimes deceptive as to the eating qualities of the fruit As an instance, one plum that I have named the "Fraud" is extremely beautiful to look at, but its flavor is that of vinegar. There is, of course, a great range of variation between different plums — even aside from those that rank as prunes — in the matter of sugar-content. Some are very sour and require a great deal of sugar when cooked; others require almost no sugar, except possibly to bring out their flavor. Taste and aroma are so closely associated that they may be said to be almost identical. They simply represent the same thing as interpreted by different organs of sense. It is obviously desirable [190] Ideal Form with Flesh to Match This is Mr. Burbank's delicious American plum, a com- plex hybrid which bears fruit of a remarkable uniformity, almost ideal as to form and bloom, and having the rich yellow flesh most admired in plums. It is a fruit that deserves its name. LUTHER BURBANK that a market fruit should have an attractive aroma, for both market man and customer often judge the fruit by this quite as much as by the taste. Closely associated with the flavor of the plum is the matter of a chemical content that will resist fermentation. A fruit that is too juicy and does not contain enough sugar will ferment very easily, as we have seen in connection with our studies of the prune. Some plums are peculiarly subject to fermentation, particularly if bruised in any way. Plums that contain plenty of sugar are, as we have seen, resistant to fermentation. This is one reason why prunes have gained in popularity for shipment in the fresh state to the eastern plum market. There is a good field for investigation as to the particular qualities, in addi- tion to sugar content, that tend to make a fruit resist fermentation. In general it is observed that insipid fruits decay first. Highly flavored acid fruits as well as very sweet ones tend to resist fermentation. But the precise chemical conditions that have to do with this very important property of resist- ance to decay have been but little investigated. All that the prospective orchardist can do at pres- ent is to select varieties of fruit that have been shown to have good marketable qualities. [192] An Example of Even Ripening The Red Ball Plum shown here approaches the ideal for market purposes, which requires that the plum not only ripen evenly throughout its flesh, but that the individual fruits ripen simul- taneously. With such a fruit, the entire crop may be gathered at once — a very obvious advantage to the shipper. LUTHER BURBANK Finally, there is the matter of the stone. In the case of the very soft plum, the stone may serve a useful function in giving support to the fruit. But the stone may be somewhat smaller than it com- monly is and still give adequate support. In the development of stoneless plums it will be neces- sary to bear in mind that the removal of the stone to some extent takes from the fruit its natural support, and the plant developer will select with intent to increase the firmness of the pulp of the fruit. Where the stone is retained it should be free, particularly in the case of the plum. The advant- ages of a free-stone fruit are obvious to every fruit eater. Varieties of plums have been devel- oped in which the stone becomes practically detached from the fruit on ripening. There is now no reason why the orchardist should not include free-stone among the qualities that he demands of his ideal plum. If to these qualities of root and branch and leaf and flower and fruit we add the one comprehensive requisition that the texture of tree and fruit alike should have the undefinable quality that makes it resistant to disease, we have perhaps summarized in broad and general outlines the most essential qualities of the ideal plum. It may properly enough be said that no plum [194] ON THE IDEAL PLUM hitherto developed can measure up to the maxi- mum or ideal standard as to each and every one of these qualities. The production of a variety that will meet these requisitions remains for the plant improver of the future — perhaps of the not distant future. Meantime it will, I think, be admitted by those best competent to judge that there are some of my hybrid plums, notably, for example, the Wick- son, the Formosa, and the Santa Rosa plums, and the Sugar, Standard and Conquest prunes, that, in their respective fields, make a fair approxima- tion to the ideal standard. There are plums in the orchard that excel all these in some respects, but have not as yet all the qualities in combination. — Building an ideal plant of any kind is like building a house. Each must be planned in accordance with a clearly conceived idea. But there is this great difference: in the case of the plant you must wait for Nature to supply you with the material with which to build. Seedling Red Leaved Plum One of the most striking of plum seedlings, being the result of Kelsey, Cerasifera, and Triflora crosses. The mag- nificent reds of leaves and fruit make a strikingly handsome and effective combination that is as pleasing as it is unusual. New Plums and Prunes in The Process of Making Some Suggestions on Which Others May Build N one occasion a nurseryman who had bought a number of fruit trees from me stopped before a tree in my orchard and tasted the fruit with the air of an expert. "That's the best plum I ever tasted," he said, as he looked at the tree with admiring eyes. "At last you have a perfect plum. It has just the right amount of fruit on it; the taste is perfect! Sell me that tree and I will make a fortune from it." "It's not for sale," I was compelled to answer. Thinking I wanted a fancy price, he started to figure what he could pay. I interrupted to tell him the faults of the fruit. It could not be shipped; it would not bear with any degree of certainty. He had chanced to see the tree on the very day in the year when it was on exhibition at its best. We had had a week of cool weather and all the plums had ripened slowly [Volume V — Chapter VII] LUTHER BURBANK together on the tree; they had responded to ideal weather — and produced a beautiful fruit of su- perior flavor. But conditions are not always ideal by any manner of means — and this plum could not stand adversity. The next year the would-be purchaser saw the same tree — coming, in fact, for the further obser- vation of it — and found the fruit worthless. For three days we had had unusually warm weather, and the fruit lacked quality. My estimate of it had been verified. I tell the anecdote to illustrate the need of cau- tion in judging a new fruit. The work is not over when the plum is produced; the fruit must be tested under varying conditions and in successive seasons. But, of course, there is no great difficulty in applying the final tests. That requires only pa- tience and open mindedness. The real difficulties were encountered at an earlier stage of the experiment. What some of these difficulties are, and how they may be overcome, will be told in the succeed- ing pages. We have considered the ideal plum somewhat attentively from the standpoint of mar- ketman and consumer. Let us now regard the same subject from the standpoint of the orchardist and plant developer. [198] ON NEW PLUMS AND PRUNES The first step in plum improvement obviously involves propagation by seeds. In my own work great effort is made to secure seed of the best varieties at the outset. As we have seen, seedlings from cultivated fruits always show a wide range of variation. Such variations offer opportunity for selection. An Outline of Methods The simplest method of working for improve- ment is to select the best seedlings thus obtained, without attempting pollenizing experiments. An extension of the method calls for cross fertilization within the species — followed, of course, by selection. A yet bolder method, and one calling for much more time in the work of selection, may be used — that of hybridizing individuals of different species. Finally the method may be so elaborated that several of the best varieties of different species are intercrossed to form new varieties. The plum "Combination," as an instance, combines the char- acteristics of three widely varying species and of numerous varieties within these species. Most of my recent plums carry the strains of many diverse species. This perfected method has been little used by other plant originators, but its practicality and value are demonstrated in my orchards. [199] LUTHER BURBANK The wide range of results attainable when these methods are used is shown by the fact that I now have plums the flavor of which is very simi- lar to the following fruits: peach, apricot, apple, pear, lemon, orange, banana, pineapple, and ber- ries of various kinds. In addition to these, there are flavors that can- not be described because they are unique — due to new combinations or blends. Although the flavor of a fruit is only one of its important attributes, it sometimes determines the value or lack of value of a new variety, and it is always an important factor. In many cases I have produced new varieties of plums which were good in every respect except the flavor, and because of this one defect they were destroyed. Plums in my present colony are of every imaginable color and quality and ripen at all seasons from the earliest to the latest. Some trees have green foliage and some have purple. The trees also differ in growth in almost every imagin- able way. Some are adapted to cold climates, some only to warm. Some require much moisture. Some will thrive under semi-arid conditions. A few give promise of being adapted to such a vari- ety of climates that — like the Burbank plum — they may be grown practically throughout the plum- growing regions of the world. [200] « <» ft 2 BS e IT* o' " ~ * a •a ** * a e; ^ * » 3 "* g a «* =• 9 a S c a 3 a a a ■ai n.32 3 R •* • o b i a-a e-a » a* is* E? m n n ~ 3 CO "1 LUTHER BURBANK And the explanation of this diversity is found in the wide range of ancestral strains that have been blended to produce this versatile company. Europe, Asia and America have furnished the foundation materials upon which have been built the sixty-two varieties of plums, prunes, and plum- cots that have already been sent out from my experiment grounds since the first importation of Japan plums in 1885. The Asiatic plums have been the most used, thirty-eight of the varieties introduced being developed from them. Fourteen introductions were developed from American, and thirteen from European species. Native Raw Materials A good deal has been said in earlier chapters of the influence of foreign blood in our plum family. Let us now give recognition to the contri- butions of the native stock. The native plums of America, although usually of a good flavor, are not nearly as large as the Asiatic species, and usually not as large as the American cultivated plums, and no larger than the wild ones from Europe. But they possess the important characteristic of hardiness. For this reason, it has been neces- sary to use them in many cases to combine with more lender species in order that the new varie- [202] ON NEW PLUMS AND PRUNES ties might become standards in the colder sections of the United States and other countries. Six important American species have been used in these experiments: They are known as the American plum (Primus Americana), the Wild-Goose plum (P. hortulans), the Chickasaw plum (P. angustifolia), the Western Sand Cherry (P. Bessevi), the Beach plum (P. maritima), and the California wild plum (P. subcordata) . These were the native wild plums of the mid- dle western states and the Rocky Mountains south to the Gulf of Mexico. Most of them are unusu- ally hardy. Cold does them no harm even in the northermost part of the central division of the United States. As to quality of fruit, these wild plums differ, but all have attractive flavors, and these flavors have been blended variously in no fewer than eleven new varieties that I have thought worthy of introduction. Anyone who has experienced the delightful flavor of my plums, Gold, Shiro, Geewhiz, Duarte, or America, will be interested to know that these new varieties (along with seven others) are Amer- ican plums, reconstructed through combination with other species, but owe their flavor largely to their wild American ancestors. To develop the earliest plum in existence from r203] LUTHER BURBANK six species of later plums seems an impossibility. Yet this is what happened when the Wild-Goose type was combined with five other late-ripening species. The plum introduced from this complex combination has been aptly named "First." It was the first introduced variety in the making of which the Wild-Goose had a part, and the first plum to ripen of all those grown in California at the time of its introduction in 1901. If the Wild-Goose plum is mentioned, the Chickasaw should not be overlooked; for al- though it has not served in the production of any introduced varieties, its hardiness has contributed valuable attributes to many varieties still in the proving orchard. But perhaps the greatest interest attaches to the story of the little Beach plum. In its wild state this is not much sought; for its fruit varies from the size of a large pea to that of a small hazel-nut, and it is inedible unless cooked. Yet this little plum has some flavor; it makes pre- serves of delicious quality. The results produced on nry grounds with this species are so important as to indicate that the Beach plum is highly valuable to use in the de- velopment of new plums for cold climates. I have produced four important varieties in which it is one of the parents. [204] ft 2 ~ 3 •"- "* "» r~ O 2^ •O 3 1 to TO •"• E TO ^ to 2 ft s TO *-. «— 3 3 ft -•2.^2- ? i § ° c* 3* ~ « "*-.«•§ 2 S S. 5 ~*32 3 3" *t C B J* ft •53 ft 3 a« © Is.'1'5-! If losS 3 5a 2 -« ft a o * n a""" * *3 ft) o i:.52 2.i ™ a 3 5'."? 9* * Si3KS. 5 ft"a m ? a a a ft 2 *» St> 3 5"' a* a, «, •* S33g ~. ft a* a* a- ~ * — H C8 SgS.5. *§ 3g* i a <» 2^ 3 « 3 s. ■5 S LUTHER BURBANK longer, smoother, and larger leaves, lighter col- ored wood, and longer and more slender branches. These hybrid seedlings are easily distinguished the first season, as the Beach plum has red roots, while those of the hybrid vary, most of them being lighter. Beach plum seedlings, no matter how young, from seeds crossed with other varie- ties, show various shades between the pale yel- low or brown root of the European and Asiatic varieties and the red root of the wildling, and if there were no other test this would be amply suf- ficient to prove that the plants were hybrids. Such, then, was the parentage of the Giant Maritima, which first bore fruit, as already noted, in 1905 — fruit over two inches in length. When I first came across this enormous fruit on a tree with the Beach plum foliage and blooming habits, the branches literally hanging in ropes of gigan- tic fruits, I could hardly believe my own eyes. The fruit begins to ripen here early in July, and when ripe it is a deep crimson, covered with a thin pale bloom. The flesh until fully ripe is very firm and solid, but it breaks down quickly when ripe. It is honey-yellow, with a pale green- ish tinge. The quality is good. The fruit is fra- grant, and as large as the Kelsey, Wickson, Cli- max, or any other plum known in 1905. It is found necessary to thin the green fruit [210] ON NEW PLUMS AND PRUNES carefully, otherwise the tree would be crushed with its weight of fruit. It has been grafted into numerous older trees, and appears to be a strong grower. Having originated from such an unusu- ally hardy wild stock on one side, it will no doubt produce a crop of fruit almost anywhere. In it- self, however, this will never prove of much com- mercial value, as it lacks firmness of texture. The Beach Plum in Other Combinations The wild Beach plum was also crossed with my Combination plum, which has in its ancestry plums of almost every type. The resulting seed- lings were not as good as had been anticipated, but two were very much liked by a well-known California fruitgrower, and were sold to him in 1908. One of these was given the name "East." It is a prolific variety. The fruits are globular, pale yellow, half covered with a crimson bloom and numerous indistinct dots. The flesh, pearly yel- low in color, is of good quality, though probably inferior to some of the best Japanese hybrid plums. The fruit ripens here from August first to fifteenth. This was tried at San Jose for several years, but found to be too soft for shipping. It is, how- ever, a desirable variety for home consumption. It has never been offered to the public. [211] LUTHER BURBANK The other plum from this cross is known as "Pride." It also proved to be of little value as a shipping plum. It ripens too quickly, so that it will not stand shipping any great distance. Pride is apple-shaped, which is usually a de- sirable form. It is a good grower, an excellent bearer, and ripens about July 20th. The skin of the fruit is a deep red with a whitish bloom. The flesh is a dark red — showing a Satsuma cross — and of excellent quality. Besides these, nearly two thousand other promising Maritima hybrids are now being grown from these crosses. Many of them are excellent in habit, productiveness, and hardiness. As yet they have not been sufficiently tested to warrant their introduction. Tribute from the Sand Cherry Another native American plum which is as hardy as the Beach plum is Prunus bessevi com- monly known as the Western Sand Cherry. Al- though it is called a cherry, it is really a plum and has been successfully crossed with the plums, as pointed out in an earlier chapter. It is thoroughly hardy in the central and northern states, and is found most often in Minnesota and the Dakotas. My work with this variety has not been so ex- tensive as with the Beach plum, but has resulted in the development of one new plum which has [212] 2 a. £.5 re «5 f a « «« 3 re ic5 a o o B » E r& ft *■* »c,i S: 2 a -S3? « a a-*?"" 3gSn a -o c a 2 <2* ™ <-■ I la Is' ^3 re "* £ ~ ^* EL £f » ^* '■*■» a 3 w -i © :. "a ti a- ... a- a--. 4 IS- ^3 LUTHER BURBANK been thought worthy of introduction. It was of- fered in my catalog of 1911-12 under the name Epoch, and is described there as follows: " 'Epoch' should be one of the hardiest of all known plums, as it is a cross of the western Sand Cherry and the American plum, both being about as near 'Arctic' plums as can be mentioned. "The tree is a compact grower, dwarf, with dark brown wood, which always, without fail, produces ropes of fruit, each fruit one and a half inches in diameter, beautiful crimson, with shades and dots of yellow. Flesh pure deep yellow, firm, with a rich cranberry flavor, but sweeter, and when ripe very good. Ripens August 15th. The youngest, as well as the oldest, trees literally cover themselves with fruit, which keeps remarkably. Probably the most productive and best of all the 'Iron Clad,' extremely hardy dwarf plums." As this variety has not been introduced long enough to get reports from growers in various parts of the country, it is not possible to say just how valuable it will prove to be. Its hardiness, however, is well established, for it has been grown in North Dakota, where the young trees have en- dured a temperature which no other plum had been able to live through. This work of developing hardy fruits for the colder sections is being pushed by other workers. [214] ON NEW PLUMS AND PRUNES Professor N. E. Hansen, for example, of the South Dakota Experiment Station, has been working for many years, especially in crossing the Sand Cherry with some of my best hybrid plums and with other varieties. He has been successful in producing several good varieties. It is to be hoped that others will enter into this work, as hardy fruits are much needed in many northern regions of our country. The California Wild Plum Almost every imaginable flavor is to be found among the California wild plums. Some are quite sweet, some are sour, others are distinctly bitter. A few are delicious. The fruit usually is small and round, about the size of the wild plums of the Mississippi Valley; and of brilliant red color, or sometimes yellow, and rarely purple. Strange as it may seem, the best fruit is pro- duced abundantly where the trees are growing on rather poor soil. The trees in different localities (and the same is true in a measure of each tree in the same lo- cality) seem to have an individuality of their own, a somewhat characteristic condition with our Cal- ifornia wild trees and shrubs. Some of these plum trees grow large and tall, with a straight, upright habit. Others form spreading bushes of low, compact growth that often bear abundantly [215] LUTHER BURBANK when only a foot or two high, bending to the ground with their burden of fruit. Under cultivation this plum has improved, and some selected seedling varieties are of very su- perior quality. Some of these plums when cooked have a flavor closely similar to that of the best cranberries, which they resemble also in color. When crossed with the Japanese, American, and European plums, a large and handsome fruit is developed, the form being usually nearly glob- ular, but sometimes oval. The trees of these crosses are also greatly improved over the wild ones in form, size, and symmetry of growth. They are always hardy and vigorous, and are as a rule exceptionally prolific. For jellies and canning, these hybrid fruits are probably superior to any other class of plums, and a few of them are most excellent when eaten un- cooked. In particular one which I have recently distributed under the name "Nixie" is valuable for use in any form. The California wild plum has also had an im- portant part in the production of the new varie- ties known as Combination, East, and Glow, all plums which exhibit the superior quality of the wild parent. Thus have the native plums of the United States been used in producing new varieties. [216] ii «) ~* *-. h «• a •a «» 2. 3. g a £. 2 S a '3'2 a 5* ■ Co *» ™ © BOO n n 3 - ©"a g.g.3 §•*§ a *» b 3 e.S^a^.'1 2. <* a ■ i£r^ a : «. S.JS » « a :r re ™ re re re 2 15 a t« a a ~- 5 o ;r-«a r* a (» i *0 C 3 LUTHER BURBANK The only variety I have introduced which is a seedling of this plum is a cross with the Asiatic Prunus triflora. This hybrid is called Doris. There is blood of the French Cherry plum, how- ever, in some hybrid plums including my well- known Shiro and a few others. The European plums have also contributed largely to the production of new races of fruit trees that are highly ornamental. A whole race of plum trees beautiful enough for lawn decora- tion has sprung into being in my open air lab- oratory. The French plum with purple leaves, Primus pissardi, formed the basis for the development of these ornamental fruit trees. The methods used in developing these hybrids are the same as with the others, and results are similar, although the fruits have not proven so generally valuable as certain varieties raised solely for fruit. The main use of the purple-leaved plum is for decorative purposes, but the fruits of the two va- rieties introduced are good enough for home use and in some cases are sold in near-by markets. This refers more especially to the very early pur- ple-leaved plum, the Othello. The story of the stoneless plums, which also owe their origin to European stock, has been told elsewhere and need not be repeated here. [222] ON NEW PLUMS AND PRUNES The unique form of the apple plum, the de- lightful Bartlett pear flavor of the Bartlett plum, the appetizing color of the Santa Rosa, and the large size and remarkable shipping qualities of the Wickson would not have been developed had it not been for the use of the Japanese species Primus tri flora. Tribute from the Orient Indeed, the Japanese plum stands as part con- tributor to thirty-eight varieties added to Amer- ican horticulture. These thirty-eight plums have been sent out from my farms, and few nursery catalogs list more than four or five Japanese plums other than these varieties, although several have been developed by other workers. China, as well as Japan, has furnished ma- terial for the development of highly valuable plums. The well-known varieties, Maynard, Cli- max, Chalco, Santa Rosa, and Formosa, and many other newer seedlings, have in their make-up the blood of Prunus Simonii, the Apricot-plum of China. This fruit takes its name from Eugene Simon, who introduced it into France from China in 1872. It was distributed in this country about 1881. It is peculiar in shape, being a large, flat, tomato- shaped plum, with dark brown, hard flesh, pur- plish-red skin, and a small stone. [223] LUTHER BURBANK The fruit is sometimes eatable, and sometimes classed as good when grown in the hot, dry cli- mates of the interior valleys of California. Its merits and defects were outlined in an earlier chapter. Here I will only add that it is by no means necessary to have a perfect fruit to begin your experiment. I have in many cases devel- oped the very best of new fruits from two nearly worthless ones. In selecting the Simon plum for these experi- ments, its value for plant improvement was con- sidered and not its value as a market plum. As a result of its use, its small stone, delight- ful aroma, and desirable tree characters have been imparted to a new race of plums, several of which have already added thousands of crates a year to the shipments of the principal plum grow- ing sections. Others even more promising are still in the test orchard awaiting final approval. Such, then, are the materials that have been utilized in the development of new fruits in my plum orchard. I have used the native plums of the Middle West, the worthless wild plums of the bleak coast of Labrador, the plums of the Pacific slope; those which our forefathers brought from Europe; a worthless, wild, half-stoneless plum; plums from Japan, some with red flesh; other [221] Eli i a ° a 5 S P" ft,-* ft. n a* lis a< © ■"» ** 5" a 2 «•'"» 5 8. B ??2 §p * s 7*a a. S3 ^ ? a •« s a 3 £.:> ■a *> ~ £■*£ a * S 2 ? s LUTHER BURBANK Japanese and Korean varieties with large bright colored fruits and delightful flavors; the apricot plum from China, the purple-leaved plum from France and the cerasifera, which has been grown mostly for grafting stocks. Although some of these species are insignifi- cant in themselves, their characters by combina- tion and careful selection have had a share in making fruits of the rarest qualities. And the work, notwithstanding its notable re- sults, is only at its beginning. The Mystery of the Bud In completing this outline of the methods of plum development, let us now consider a little more in detail an aspect of heredity which con- cerns equally all our other cultivated orchard fruits, and which must seem mysterious to every- one who gives the subject a moment's considera- tion. I refer to the familiar but extraordinary fact that whereas the bud or cion of a given tree will reproduce the fruiting qualities of the parent with the utmost fidelity, yet the seedlings grown from the fruit may have the widest diversity. It has been pointed out that you need not hybridize the orchard fruits in order to get new varieties. The seed of almost any plum tree, for example, will give you seedlings a plenty that are different from the parent tree. [226] ON NEW PLUMS AND PRUNES That the germ plasm of a single tree may thus contain the potentialities of a hundred different types of future fruit, is a mystery to which we have referred, but to which we may recur without apology. When we further reflect that the branch in question, which carries this amazing heritage, perhaps grew from a single pea-sized bud inserted on the trunk a few seasons ago; and that the tiny bud in question must have contained, pre-de- termined within its seemingly insignificant sub- stance, all the potentialities that will be revealed in all the different "varieties" of its progeny, the mystery becomes still deeper — if comparison be permitted between the various aspects of a subject every phase of which lies almost beyond the bounds of human comprehension. But even though we cannot hope fully to understand, much less to explain, the mysteries of heredity of which the case of the bud furnishes a familiar yet striking example, we cannot help pondering on the matter. And as nowadays we are accustomed to associate function with struc- ture everywhere in nature, seeking a physical basis for the observed phenomena associated with life processes, it is natural that here as elsewhere at- tempts should have been made to visualize the conditions that obtain in the germ plasm of the [227] LUTHER BURBANK plant, and to picture in imagination its actual mechanism. In our age the telescope, fortified by the weirdly penetrative spectroscope and aided by the photo- graphic plate, has enabled the astronomer to reach out into unthinkable realms and to record not merely the direction and speed of light but even the chemical composition of stars so distant that their light, traveling 180,000 miles per second, re- quires scores of years to reach the earth. With the aid of the same instrument, the universe is proved to be peopled with dark stars, definitely revealed to us even though forever invisible; the structure of the universe as a whole is coming to be understood, and the course and direction and speed of groups and streams of stars by millions have been tested and charted. In such an age it is not strange if the worker who turns his eyes in the opposite direction, and attempts to penetrate the mysteries of the micro- cosm of the plant or animal cell should have found means to pass beyond the range of vision of the microscope and reveal something of the intimate nature of the events that are taking place in the world of molecule and atom and electric particle. Aid from the Microscope In point of fact the invasion of the world of the infinitely little by the modern biologist has [228] Early Crimson Plum Fruits This particularly realistic direct color photograph print shows a plum which bears unusually early, and which reveals in its characteristics a combination of the wild California, European, and Japanese plums. The strains of the different an- cestors are blended in very complex combina- tions, through repeated crossing. LUTHER BURBANK been no less wonderful than the exploration of the world of the infinite vastness by the astronomer. And perhaps it should not seem strange to any one who has a philosophical conception of the underlying harmonies in nature, that the condi- tions revealed in the microcosm of the living cell should suggest in many ways an epitome of those made manifest in the macrocosm. Such, at all events, is the message that the modern biologist and physicist bring us from the world of infinite littleness. Making the first stages of their invasion with the aid of a microscope, they show us that all living tissues, vegetable or animal, are composed of cells, and that within each cell there is a vitally important central structure called the nucleus. This structure lies at the heart of every germ cell through which a living organism propagates its kind. The pollen grain of the plant, for example, is the carrier of such a germinal nucleus. The pollen grain itself is a structure of almost microscopic size, yet it is colossal in comparison with the in- finitesimal fleck of germinal matter that lies at its center. Yet the modern microscope can so mag- nify this fleck of matter that something of the mechanism of its vital parts becomes visible. The microscopist tells us that within the germi- [230] ON NEW PLUMS AND PRUNES nal nucleus there are to be seen sundry films of matter, arranged to form a sort of skeleton, which are readily stained under his manipulation and which he therefore names "chromosomes", colored bodies. He observes that the nuclei in the cells of different plants and animals have these infinitesi- mal chromosomes arranged in different character- istic groups, differing in number in different species but always the same for each and every cell of plants or animals of a given species. The enlarged vision of the microscopist enables him to assure us that when two germ cells of the opposite order come together — when, for example, the nucleus of a pollen grain blends with the nucleus of the plant ovule — there are various char- acteristic dividings and interlinkings between the two sets of chromosomes within the two nuclei. In the blending and rearrangement of these minute structures, he believes that he is witnessing the underlying processes that bespeak the blending of hereditary potentialities and their re-combina- tion to determine the future possibilities of the new organism that is thus brought into being. All this is very wonderful. But it brings us after all only one stage nearer the confines of the mys- tery. The chromosomes within the nucleus, which all biologists nowadays regard as the tangible car- riers of hereditary tendencies or capacities, are [231] LUTHER BURBANK few in number, and small as they are, we are forced to conclude that each of them must be the carrier not of a single potential trait or tendency but of a multitude of such potential traits or tendencies. Our practical experiments in plant breeding have shown us that we deal often with a dozen or more tangible characters that are grouped against each other in opposing pairs — definitive qualities of size or color or flavor of fruit and all the rest — and it requires but a moment's thought to see that each of these "unit characters" is in reality made up of a multitude of minor characters. Heredity carries all of these definitely from one generation to another; so their potentialities must be represented within the structure of the chromosomes; and there are by no means chromosomes enough to supply one for each hereditary character. So we are obliged to assume that each chromosome is in itself a complex structure, and that within that structure there are subordinate structures — like the individual bricks and boards and nails and rivets that go to make the structure of any piece of human architecture — that deter- mine by their quality or their arrangement the specific potentialities of the future organism. Each chromosome, in other words, must be thought [232] The Home Chestnut Plum Like all Mr. Burbank's recentlg developed new varieties, this is of complex ancestry. It is less celebrated than many other varieties that have been developed at Sebastopol, but it has qualities that make it an admirable fruit for the door yaj-d and home garden. LUTHER BURBANK of not as the tangible conveyer of any particular "unit character", but as a receptacle in which several or many factors or determiners of diverse unit characters — size of flower and color quality of leaf and fruit and all the rest — are assembled. Further Aid from the Physicist But unfortunately the powers of the microscope do not suffice to reveal these unit structures within the chromosome. What they are like, must for the present remain only a matter of conjecture. But that they are definite mechanical structures of unthinkable smallness, represented by chemical atoms in specific combinations, we can not doubt. And in revealing to us the size and character of these atoms, the modern physicist gives us aid in supplementing the vision of the microscopist and in helping to make it seem at least a possibility that the definite factors of heredity have a physical basis within the microscopic chromosomes. The conclusions that give this assurance are based on various almost infinitely delicate tests that are made in the modern physical laboratory. Summarizing these in a few words, it appears that the physicist and chemist are now able to make definite computations as to the size of the molecules and atoms that make up the structure of all matter. And the figures they present, when [234] ON NEW PLUMS AND PRUNES they have taken a census of the atom, are such as to give us full assurance that even so small a struc- ture as the minutest chromosome within the nucleus of a plant cell contains molecules and atoms in such numbers as to make possible an infinite complexity of arrangements and therefore an infinite diversity of resulting qualities. Thus we are told that the smallest particle of matter visible under the magnifying influence of the most powerful microscope is of such dimen- sions that 50,000 of such particles placed in line would be required to cross the space of one centi- meter or about two-fifths of an inch. If we calcu- late the cube of this number we find that 125 thousand billion such particles could be crowded into the space of a cubic centimeter. But it further appears that, according to a definite measurement made by Professor Rutherford, more than 20 billion times that number of helium atoms would exist in the form of gas in the same space. And the commentator I am quoting adds : "Of course the molecules of gas are widely separated. So it follows that the smallest particle of solid matter visible through the most powerful micro- scope contains many times 20 billion atoms." "Many times 20 billion atoms" in the smallest particle of matter that the microscope reveals! Vastly more than that number of atoms, then, in [235] LUTHER BURBANK each individual chromosome of the group lying within the nuclei of pollen grain and ovule — since these are by no means at the limits of visibility. And each atom has itself specific individuality. Each group of a thousand atoms or so might make up a molecule of a different type of protoplasm. So here is material for millions of kinds of protoplasm, were so many needed. Here within the infinitesimal germ cell, re- vealed to us in part by the microscope of the biolo- gist and for the rest made manifest in imagination by the revelations of the physicist, is material enough to supply tangible carriers for all the con- ceivable hereditary factors that come to make up the most complex organism of any plant, or for that matter of any animate creature whatever. The Germ Cell A Complex Organism Let us make the illustration specific. Suppose that the chromosome in the nucleus of any given pollen grain — say that of a plum blossom — were of the very smallest size visible under the micro- scope. Suppose, also, merely for the sake of illus- tration, that the hereditary factors for unit char- acters that it bears are of a thousand different types — representing all details of size and color and foliage and growth and leaf and blossom and fruit of the future tree. We know that the chromosome really does bear these potentialities; [236] LUTHER BURBANK I am merely assuming their number at a thousand individual units for the sake of illustration. In our former views, when we considered the transmission of complex qualities by the infinitesi- mal pollen grain the thing seemed utterly inscrut- able and mysterious. But now with the aid of the new facts that the physicist has supplied us, the mystery is somewhat clarified. He shows that the smallest visible bit of protoplasm must contain at least twenty billion atoms. So there would be enough of these atoms to supply no fewer than twenty million to make up the structure of each individual hereditary factor. Now twenty million bricks, of ordinary size, piled solidly together, would make a mass 100 feet square and 300 feet high. So the structure of each hereditary factor of all the thousand in our infinitesimal speck of germ plasm may be as complex as any building that could be made with such a pile of bricks as that — and more complex, no doubt. Add that each individual atom in our germ plasm structure is no crude brick but is conceived by the best informed students of physical science to be "at least as complex as a piano", and we gain a yet clearer conception of the possible intri- cacies of the mechanism of sach of our imagined thousand hereditary factors. [238] ON NEW PLUMS AND PRUNES In this view, then, the germ cell may well be an organism as complex and of as definite a system of architecture as the full grown tree into which it will ultimately develop. The leaves of a tree — even the leaves of a forest — are a meagre company compared with the census of the atoms within the nucleus of a single germ cell. An Amazing Microcosm Nor need we limit our view to the germ cell that produces a single plant. Let us consider for a moment the bud from which the branch grew on which are produced, according to our illustration, plums, the seeds of which may give rise to some hundreds of different "varieties" of fruit. Do the analyses of miscroscopist and physicist make comprehensible the fact that the original bud of the plum tree can contain potentialities of so many different complex structures? Another glance at the figures of the physicist will supply an answer that would have been be- wildering were it not for what we have just seen as to the complexity of the germ plasm. It appears that, according to the estimates of Professor Ruth- erford (based on accurate count of the atoms given out as so-called alpha particles in the radia- tion of radium) the mass of an atom is so incon- ceivably small that the number of atoms making [239] LUTHER BURBANK up a portion of matter as big as our plum-bud (which we may assume to have the bulk of about a cubic centimeter) is represented by the figures 68 followed by twenty-four ciphers — 68 "octil- lions", if the figures must be read. So the number of atoms that are aggregated in the tiny plum-bud is vastly greater than the total number of people that have lived on the earth since the human race was evolved. To attempt to give tangibility to the idea of the smallness of the atom, we may borrow an estimate made by the late Lord Kelvin. It may be computed that if the tiny plum-bud were imagined to be enlarged in size until it became as big as the earth, each component atom being increased in the same proportion, its entire structure would then be made up of units (magnified atoms) of about the size of footballs. If we then reflect, further, that according to the definite analyses of other physicists, with Sir J. J. Thomson of Cambridge at their head, each atom is itself a complex structure — the very simplest atom, that of hydrogen, being composed of at least 1,700 particles called electrons which are in reality the unit particles of electricity — we shall gain a still more enlighteniug view of the complexity of our plum-bud microcosm. It has been estimated by a French physicist, [240] LUTHER BURBANK Becquerel, that the size of the individual electrons that make up the atom is such that they may be thought of, not as piled solidly together within the structure of the atom, but rather as infinitely separated by comparison, like a swarm of gnats flying about in the dome of a cathedral. It is a little difficult for anyone not accustomed to this particular use of the imagination to follow the conceptions of the physicist. But we may accept his findings as authoritative, for they are the result not of one man's work alone but of tests that have been applied by many workers. Making the application to our plum-bud, then, it appears that its bulk is such as to give us assur- ance that it contains (although it actually is no larger than the smallest pea) a number of atoms so great that if the atoms were conceived to be all gathered into 8,000 different groups (each group representing a different variety of future plum), there is material enough to supply at least eight million billion atoms in each group ! And each of these atoms is itself a complex structure made up of several thousand electric corpuscles. Now we know that each particle of protoplasm, the physical basis of all life, is composed of atoms of carbon, hydrogen, nitrogen, and oxygen in com- plex combinations. A single molecule of proto- plasm may contain a thousand or more atoms. [242] ON NEW PLUMS AND PRUNES But even allowing a thousand atoms to each molecule, we have ample material for the con- struction of something like eight million billion molecules for each one of our 8,000 groups of potential plum trees. Obviously there is abundant opportunity for the combination of such material into complex groups, quite adequate to account for the different qualities of our various plums — be they never so divergent as to form or size or color or flavor. The Bud as A Walled City In this expanded view, then, it is no more wonderful that a pea-sized plum-bud can contain within its germ plasm the potentialities of hun- dreds of varieties of future plums than that a city can comprise hundreds of houses, no two just alike, all built of wood, brick, stone, and metal in different proportions and combinations; just as the germ cells are all built of the atoms of carbon, hydrogen, nitrogen, and oxygen in different com- binations. There are far more bricks (atoms) available to build each different type of germ plasm in our plum-bud colony than are required to build the largest structure in the man-made city. The real wonder, as I said before, lies in the fact that each infinitesimal aggregation of mole- cules of protoplasm has the capacity to take to [243] LUTHER BURBANK itself stray atoms that are brought into its neigh- borhood, shape them into its own structure, some- what as a brick-layer shapes the bricks into the walls of a building, and thus increase constantly in size. It is this capacity of the germ plasm to gather material and utilize it in expanding its structure — together with the further capacity to move in re- sponse to environing forces — that is the underlying mystery of the entire life-process, including the interesting aspects of it that we see manifested through heredity. In a word, a fruit-bud is a walled city tenanted with a multitude of complex structures, and the mere size of the bud, in our clarified view, has nothing whatever to do with the wonder of its composite architecture. The phenomena of the germ cell have hitherto appeared peculiarly mysterious simply because our blunt human senses deal ordinarily with masses of matter of a more tangible size. Now that the microscopist and the physicist have opened the way for us into the microcosm, we see that mere size is of no great significance in the matter, and that there is ample opportunity within the nucleus of the smallest germ cell for an or- ganization of molecules and atoms that for all practical purposes may be at once as complex and [244] S.3 K 5 « p, ~- o. a- ^ S5"' » X 3'» 5 o S. *> ** *1 Ok is n> __ si*;* oS » -J 2! n l?8 2.S-0.-5 to ~ co a a a n <* a i* •a •»■ "» Is*5"*!* <• * o.. ** o. &•* 5 •r- B i to oOS C3- «©. C a i-i. a ^ A, 3 &3 a a a "o« Co 8- © oT. a. a S,oS2.« C. . 3 , to 3" LUTHER BURBANK as definite as the visible structure of the mature plant in which the germ cell sprang or of that other mature plant into which it will develop. — The work, not- withstanding its not- able results, is only at its beginning. What The Burbank Plums and Prunes Have Earned The Opportunity Which Improvement Opens Up THE BURBANK plums and prunes have earned money for everyone except the originator. Introducers, growers, canners and shippers, transportation companies, dealers, and consumers have made and saved money from these fruits. The originator, on the other hand, as nearly as he can estimate, has received about 50 cents on each dollar invested in the work of plum development. My experiments altogether — nearly one-fifth of which have been devoted to plums and prunes — have cost me very nearly $250,000. The in- come from the sale of new varieties has been ap- proximately $100,000. Up to 1912 I was about $150,000 behind on all my experiments. But the loss on the plums has been less, probably, than that on a good many other lines of experiment, [Volume V — Chapter VIII] LUTHER BURBANK and there is reason to believe that varieties not yet introduced will presently bring a return that will more nearly balance the account. Meantime the sums earned for others by the Burbank plums and prunes after they have gone out into the world have been really significant, from whatever standpoint considered. As illustrating their earnings in a single field, we may note that in the season of 1912 there were 564 carloads of Burbank plums of different varie- ties, aggregating 396,133 crates, shipped from Cal- ifornia alone to the eastern markets. This repre- sented more than one-third of all the shipments of plums. The average price per crate received for all Burbank plums was $1.20, as against $1.03 the reported average for other varieties. The maximum price per crate for any Burbank plum was $3.25 (Wickson), as against a maximum of $3.04 for any other variety; the highest average prices per crate being respectively $1.71 (May- nard) and $1.45. The total wholesale price of the Burbank va- rieties of plums shipped in this single season was not far from half a million dollars. If individual varieties are under consideration, the plum specifically known as the Burbank ex- cels any other single variety by a large margin; the figures being, for the Burbank, 116,764 crates [248] Typical Wild Worthless Plum Seedling This is a hybrid plum that harks back to a wild ancestor. The thin wood and slender leaves indicate that it will not be a good bearer. LUTHER BURBANK and for its closest competitor 98,149, a difference in favor of the Burbank of 18,615 crates. If prices are taken into account, the lead of the Burbank becomes still more significant, the highest price per crate for this plum being $1.93, and its average price $1.12. The total revenue from shipments of this single variety of plum was more than $130,000. And all this, of course, refers to the Burbank plums merely as shipping plums from a single district. It takes no account of prunes, the han- dling of which constitutes an altogether inde- pendent industry. Nor does it, of course, refer in any way to the shipment of plums from any re- gion except California. Yet the Burbank plums are grown everywhere, and in some remote re- gions as, for example, South Africa, they are raised on the largest commercial scale. The bush- men of Australia are perhaps as familiar with the deep yellow, juicy, tender but firm flesh, and the sweet aromatic flavor of this plum as are the or- chardists of California. It is equally well-known in New Zealand, in England, in France, in Nova Scotia, and in Southern Canada, and in this coun- try it has become the standard in all the states except Wyoming. The total number of nurserymen in America who list Japanese plums is 150, and of these 142 [250] ON PLUM AND PRUNE PROFITS list the Burbank; a record not approached by any other plum. A More Comprehensive Valuation But these figures, and any others of like char- acter that might be collated, serve, after all, to give only a vague and general idea of the eco- nomic importance of the new plums. Statistics having to do with shipments to the great markets, even were they available for all territories, would tell but a small part of the story. The true benefits accruing from this work cannot be reduced entirely to figures. A large proportion of the earnings, for ex- ample, have been protective — in the nature of as- suring large and regular yields of superior qual- ity; thus giving significant returns each year in- stead of uncertain yields occasionally. Again, even the most elaborate statistics would entirely fail to present the facts at their true value, because the identity of a plum is often lost through the prevalent custom of renaming varie- ties. The Abundance plum, as an instance, has been designated "Botan," "Botankio," "Chase," "Yellow Japan," "Douglas," "Oval," and probably by other names by the growers and sometimes also by the nurserymen and dealers. The Wick- son plum has been sold under the name "Eureka," and similar liberties have been taken to a greater [251] LUTHER BURBANK or less extent with each of the 20 Burbank varie- ties that are prominent as shipping plums. Therefore the figures based on the records of distribution, growth, and sale of a variety are sure to be far below the correct figure. But most important of all is the fact that a very large part of the entire plum crop is grown for home consumption or for distribution in local markets, of which no record is available. With the wide distribution of Burbank products over the entire world, in many cases in countries where no systematic public records are kept, there are unrecorded benefits, profits, and earnings to the extent of millions of dollars annually, of which no accurate estimate can be made. And, finally, even if complete up-to-date rec- ords of the earnings of the Burbank plums could be collated, the figures would give but a vague idea of the real importance, from a purely eco- nomic standpoint, of the work that has been ac- complished, for the reason that it takes a long time to introduce a new fruit, whatever its im- portance, and the best Burbank plums and prunes have been developed within very recent years. Of my quartette of "best" plums, only the Wick- son has been on the market long enough to ac- quire anything like the reputation and the vogue that its merits justify. As to the others, Formosa [252] Small, Poor Foliage This specimen is perhaps even less desirable than the preceding one. Such a seedling may be at once discarded with- out waiting for it to bear fruit. As is said by the Yankees of poor Help, it will be found waiting for pork at sundown" instead of performing satisfactory work. LUTHER BURBANK was introduced in 1906, Santa Rosa in 1907, and Beauty, perhaps the best of all, only in 1911. So whereas we find that the Wickson was shipped from California in 1912 to the extent of one hundred carloads, there were only two car- loads of Formosa and fourteen carloads of Santa Rosa recorded, and of course Beauty is not rep- resented at all. Obviously, then, the earning power of these newest and best plums is a matter for the future. When the statistics are collated, let us say for the year 1925, it will be possible to gain a clearer view of the real importance of these new pro- ductions. Of course, orchardists are proverbially con- servative. Perhaps it is natural that they should be so, considering that they deal with trees that re- quire some years to come into bearing. An or- chard cannot be made in a season, like a grain field, but the rapid conquest effected by the Bur- bank plum and the Wickson leaves little room for doubt that my newest plums will make their way no less effectively in the course of the com- ing decade. Fortunately for the fruit grower, he may in- troduce these new Burbank varieties with less loss of time than usually attends the introduction of ordinary plums. [254] Mosaic Variation Occasionally a seedling shows a mottled leaf like this. Such a seedling, although otherwise promising, is rejected. In this case vigor of growth in the tree is indicated by the size of the leaf and wood, but a leaf of uniform dark green color is to be preferred. This is interesting, however, as showing a peculiar segregation of color factors, one of the ancestors having been a purple-leaved plum. LUTHER BURBANK All of the older varieties in an ordinary Cali- fornia plum orchard require five or six years growth before they commence to pay for them- selves. But most of the new Burbank varieties will commence to bear heavily in the third or fourth season, and by the fifth or sixth year they will have produced as much as the ordinary plum orchard four or five years older. Why Plant Creation Is Costly Since I have spoken of the losses sustained by the plant originator in developing fruits that bring such large monetary returns to others, perhaps I should explain a little more at length why it is that the plant developer who experiments as I have done cannot hope for a quick financial re- turn for his efforts. One chief reason why experimentation of this order does not pay is that it was done so compre- hensively, thoroughly, and on so large a scale. Where a man conducts plum improvement, for example, as an adjunct to a nursery business, there is no reason why he might not eventually secure even a single improvement that could di- rectly pay him for his care and expense in pro- ducing it. There would be no certainty as to this, to be sure, as the chance of securing a really good new variety is not better than about one in ten thousand. That is to say, in handling ten thou- [256] Foliage of Fair Promise These are leaves of fair shape and a good degree of vigor. This seedling may be depended upon to produce a fair amount of fruit, although perhaps not an exceptional quantity or fruit of unusual quality. It is an average specimen of the kind which is worth preserving and testing. LUTHER BURBANK sand seedlings, there would be no probability of securing more than a single good new variety. But, on the other hand, sometimes even a small lot of seedlings may give more than one good va- riety, as was the case with my original twelve seedlings from Japan. In any event, the nurseryman can carry out a line of experiment on a moderate scale without considerable monetary outlay. So at worst he will lose very little. But where innumerable crosses are made and thousands of seedlings are raised each year only to be destroyed; and where all needed improve- ments are worked for together as in the combina- tion of a great number of species and varieties — instead of taking a certain established variety and attempting to make one or two improvements upon it — there must necessarily be a much greater proportion of expense. But, so far as my own experiments are con- cerned, the pioneer work has now been done. I have elsewhere told how the material has been gathered from all over the world, until the plums and prunes of my orchard carry hereditary strains in their germ-plasm from ancestors imported from five continents. And I have pointed out that there are thou- sands of new varieties among my plum trees that [258] Typical Good Bearer The branch here shown, the essential qualities of which are admirably reproduced in the color print, may be taken as a typical example of a good bearer. This may be depended upon to produce fruit in abundance, and of the best quality consonant with its inheritance. LUTHER BURBANK have exceptional qualities, and from the progeny of which, variously interblended, many new and important races of plums and prunes will doubt- less be developed in the immediate future. The sum total of my work with the plums and prunes, judged by the record of actual introduc- tions, comprises the development of only 62 new varieties. But it must be understood that these 62 introduced varieties are only the pick among thousands, very many of which were but slightly inferior to the ones chosen. And, as I said before, the final balance sheet for my work with this fruit cannot be struck for many years to come. My plum orchard might be compared, in this regard, to a large number of modern industries, manufacturing establishments, for example, which have a high first cost and which cannot be expected to pay more than the interest on the investment for a good many years, yet which may ultimately show a profit that will pay back the original expenditure and even give a balance on the credit side of the ledger. Plant Improvements Cannot Be Patented There is, however, one feature of plant develop- ment that puts it on a different plane, as regards probable financial returns, from that occupied by most other fields of inventive or creative industry. This is the fact that nothing comparable to a [260] Typical Good Purple Leaf Plum A tree with purple leaf always contrasts pleasantly in the landscape with the usual green trees. The purple-leaved plum is a particularly interesting tree. Mr. Burbank has made experiments in combining it with the usual green-leaved plum. There is an interesting segregation of colors in the second generation of such crossbreed varieties, resulting sometimes in the mottled leaves shown in earlier plates. LUTHER BURBANK patent can be obtained on new varieties of fruit trees or flowers, such as the developer of new, mechanical inventions or chemical combinations, or artistic productions can depend upon to guard his invention and make it at least probable that he will share in the profits that accrue from its intro- duction. The plant developer must either intro- duce his new varieties through direct sales to nurs- erymen and planters, or else sell them outright for a comparatively small sum to a wholesale dealer. In the latter case he receives a sum that is never large. In the former case his returns are altogether problematical, and at best there are only two or three years during which he has a partial monopoly of the sale of the product of his labors. In three or four years, according to the rapidity with which the new variety can be multiplied, orchardists who have purchased grafting stock can compete in the market with the original introducer. Suppose, for example, that I have a new plum that I decide to introduce directly. I sell grafting wood by the foot. The highest price I have ever received for grafting wood, even of the choicest new variety, is $10 a foot. This, to be sure, is at the rate of about $800,000 a cord, if you choose to reckon it that way; but [262] gg "5 •i <» a. LUTHER BURBANK unfortunately you sell only a very small fraction of a cord. There is not likely to be any very active demand for a new variety of plants, or until it has been tested out in several localities. Meantime, the first purchaser, in making the test, has grown a large quantity of twigs from his grafted cions; and with this, obviously, he can enter the market on an equal footing with the original producer. Thus, a single foot of wood gives enough buds to graft a strong, vigorous, young tree; and from that tree enough wood may be taken next year to graft nearly an acre of orchard. After that, of course, the supply is practically unlimited. Thus the cost of securing a plum or prune orchard of the very choicest variety is absolutely insignificant; to say nothing of the fact that the enterprising purchaser, when he has demonstrated the value of the new product, can sell grafting wood to his neighbors in such quantities as to pay back many times over his original outlay — even though, as sometimes happens, he makes the sales at only a fraction of the price charged by the original introducer. In this way, it is clear, any orchardist who pur- chases cions of a new stock may quickly enter into competition with the original producer or the firm that has purchased the right. Often the second man that comes into the field may take [264] A Diseased Specimen Instead of showing the vigor that usually characterizes hybrids, this specimen shows an impoverished condition of the nutritional system, which should lead to the rejection of this seed- ling. It might be compared with a tubercular or ill-nourished animal, and it cannot be depended upon to produce good fruit. The wise plant developer would never give it an opportunity to come to fruiting age. LUTHER BURBANK advantage of the advertising done by the first, and quite possibly make as great a profit as the pro- ducer and the original introducer. And each local nurseryman may in turn take up the work of distribution, supplying the local demand. So the few feet of grafting stock that the original plant developer sold for a mere fraction of what it had cost him to produce the new variety, have within a few years multiplied to make up the thrifty branches of scores or hun- dreds of orchards, until every one who desires the fruit is supplied, without an additional cent com- ing to the pocket of the originator. This was what I had in mind when I intimated in the beginning that the most successful new fruits, which bring fortunes to a large number of dealers and growers, may represent financial loss to the originator. Incidental Profits from the New Plum Not to dwell unduly on this aspect of the sub- ject, however, let me point out a little more in detail some of the benefits conferred by new fruits having exceptional merits. For example, a fruit may make an exceptional profit for the grower merely because of the fact that it comes into bearing very early in the season, before the market is glutted with fruit of other varieties. [266] A Weakling This seedling has a weak stem and not enough leaves. It is not unhealthy, but it simply lacks vitality. It may be re- jected without further tests. LUTHER BURBANK The Burbank, Santa Rosa, Climax, and For- mosa plums, among others, are striking examples of this feature, as they come into bearing very early. Several of these have come into the mar- ket at a time when it is nearly bare of fruit. Another advantage is secured to the fruit grower by varieties that are regular and abundant bearers. Regularity of bearing is a factor for which I have worked constantly, and it has been instilled into all my new varieties of plums. These trees are not constructed on the hit or miss plan. They can be depended on to give a crop each year. It requires no argument to show that the expense of starting an orchard can be paid much more rapidly by trees that will bear abundantly each season. An enormous crop every other year would not at all take the place of even a moderate crop every year. But, in point of fact, my new plums are not only regular bearers, but most abundant bearers as well. Sometimes the grower is deceived by receiving a large price for a variety of fruit that is produced in such small quantity as to bring a meager aggregate return. The wise orchardist, however, will look for a fruit that will produce abundantly and at the same time bring a good price per basket. The Tragedy at $2.00 a crate would generally pay much [268] Leaves Showing Mixed Inheritance This is a crossbred seedling, descended from purple- leaved and green-leaved ancestors. The segregation of colors in the second generation has been referred to, and is illustrated here in a very interesting wag. Most specimens have leaves that are all green or all purple; but here and there one mixes the colors, in a way that has peculiar interest for the student of heredity. LUTHER BURBANK less than the Burbank at $1.00 a crate, owing to the difference in the productiveness of the two varieties. But, in point of fact, the Tragedy, even with its small production, averages (according to the returns of last year) only 19 cents a crate more than the Burbank. And of course the Burbank was one of my early introductions. Some of my newer plums quite outclass it in selling value. All of the most successful of my new plums are early bearers and produce large and attractive fruit. The purchaser desires a large, high-colored, handsome fruit, and he is not disappointed if he finds that it has excellent quality also. Then, in order that a fruit shall earn money for its grower, it must be adapted to stand ship- ment to a distant market. Many beautiful plums lack this quality and as a consequence never have been, or can become, valued fruits for commercial shipping by the carload. But my new plums have been developed with this need constantly in mind. I have recognized that a fruit to become of importance for shipping long distances must have a number of qualities that hitherto have not been required in fruit. It must be of texture that will not break down in handling and shipping; it must retain its flavor, or even have improved flavor if picked before it is quite ripe; and it must remain firm and hard not [270] A Tree of Vigor A typical branch of the Burbank plum showing the strong, sturdy stem and the heavy, abundant foliage. These leaves suggest strength and vigor, and in point of fact the Burbank plum is famed for these qualities. The fruit itself has been shown in earlier pictures. LUTHER BURBANK only throughout the long journey but during sub- sequent days until it can be placed among the retail distributors. Very few plums in existence to-day are wholly up to these standards of excellence. The Wickson, one of my early introductions, fulfills these condi- tions better than any other plum hitherto pro- duced. But there are several among my pros- pective introductions that will excel even the Wickson. Often one new character in a plum, prune, or plumcot doubles its earning capacity. The ship- ping qualities of the Wickson; the color of the Santa Rosa; the flavor of the Geewhiz or Nixie; the bloom of the Plumcot which enables it to be placed on the market as fresh in appearance as when first taken from the tree — these are examples of characteristics that double the earning capacity of the fruit. Incidentally, we must not fail to note that improved varieties of plums and prunes have greatly enhanced the earnings of the transporta- tion companies. Where fruit is shipped by the carload, it can be handled economically by the railways, and as transportation is an essential link between the producer and consumer, there is no difficulty experienced by the common carriers in securing an adequate price for their work. [272] ON PLUM AND PRUNE PROFITS Another minor point that might readily be overlooked is that the Burbank plums increase the earnings of the retail dealer, who not only makes a direct profit from their sale, but so beautifies his exhibit by introducing these large and hand- some fruits as to attract customers, and thus facili- tate the sale of his less attractive fruit as well. Finally, the earnings of the Burbank plums advantage the ultimate consumer. The new plums can be produced so much more cheaply that sooner or later this reduction in cost of produc- tion will rebound to the benefit of the final pur- chaser. He gets the fruit at half the former price. The fruit itself is of greatly improved appearance and quality, yet it costs less than smaller, less at- tractive, and less highly flavored plums formerly cost. So in the end the consumer shares the profit of the Burbank fruits with all the other parties concerned. If in conclusion I revert to the statement that nobody is made financially poorer except the originator of the fruit, it is only that I may add that he also receives an adequate reward in the knowledge that he is a benefactor of all parties concerned and a detriment to none. If he can only pat himself on the back, while others may pat themselves on the purse, perhaps his satisfaction after all is not less than theirs. [273] © a. 55 a © a a S-SS Si IMlS ft. « a »- ft.-- ? _ S ala*s« .5 S S £ In 53 d S 3 ii^ s a « 5 aw o — «> .2 ■2 *-*: 51 = «2 •» 3 — ,5«,«s ~2 &&* c ~ Accomplishing the Impossible —The Plumcot A Cross Which Man Had Said Could Never Be Made EVERAL years ago a party of noted scientists from various parts of the world were visit- ing my nursery. I asked one of them — an American, even then well known to the public as an authority on horti- cultural subjects — to come over to another part of the grounds and see one of my crosses between the plum and the apricot; one of my first crosses then just ripening. "There can be no such fruit," my visitor declared. "The two species are wholly different in all respects. Everybody knows it is impossible to cross two trees of such widely varying types as the plum and the apricot." I was not surprised to hear him make this statement. For at that time very few biologists — and in particular few technical botanists — had quite given up the notion that there are hard and [Volume V — Chapter IX] LUTHER BURBANK fast lines between the different species as com- monly classified. This belief has undergone a radical change, in recent years, and the many combinations of widely different species made on my Sebastopol grounds have had at least a share in broadening and clari- fying the views of the classifiers. "Well, what kind of a tree do you think this is?" I asked a moment later. "Why, a plum, to be sure." "Please examine more closely, professor," I requested. "This leaf looks to me more like an apricot than like a plum!" "Yes — yes. I see now it is; it is surely an apri- cot— the leaf, though differing from most of the apricots, is certainly an apricot leaf." "Now look again, carefully — look at the foliage, bark, branches; and now let us examine the fruit. Then tell me what you really think it is." After a long and thorough examination, I heard the reluctant decision : "Well, it surely is what you claim it to be — a cross between the plum and the apricot. I never thought it could be made." I told him I had hundreds of others of different sizes, shapes, and qualities. "Show me another — quick! quick!" And I showed him not merely one other, but a score or two, to his added mystification. [276] 3b»?s ■ 2. 2 5. 3 s. « " c ^ B -H. 3 b<2 v » 2. c ** a *La S" ?~3 3 ?-o <* , 3 re &* a a ~ &> a ~. ■;, a, a 5. ** o"5 5" ■* S'-» _, s a ~ 5 03re--2.re Co LUTHER BURBANK threatens the offspring of every wide cross. One of the first plum-apricot hybrids produced did not have a stamen on the whole tree. It was evidently a cross of the plum and apricot, but in the combination the means for perfect reproduc- tion was overlooked. Experiments were made by applying pollen to the malformed blossoms. But few ripened — the majority remaining dormant. The cross brings out this striking malforma- tion, but there are doubtless almost numberless tendencies striving for mastery that remain sub- merged, seemingly neutralizing one another — perhaps destined ultimately to come to the surface under influence of a changed environment. At every stage of the development and im- provement of a plant short cuts must be intro- duced, where time and expense can be saved. Instead of waiting years for a seedling to bear, it is possible to save much of that time by the application of well known methods of grafting, elsewhere described. Some of the most vigorous and best growers of the hybrid seedlings were grafted into older plum trees. After two or three years several of them began to bear fruit abun- dantly. The grafts showed that fruit would actually be produced — fruit of fine quality; this much was assured. [282] ■»« ft a. S. 3 3- 3S ^ re re 'a a 3 a ?:;• o » 2 " ? « *S "a «• a •3 °* 2. T- £ re O a. a- 2 S <» re 3 a* a 52 a s a « <* a re re co re ™ ^ a «• re BO Co '•• s © ft<3 ?5-a * 2. a »33i a* re «. a _« re ^ re jj a a ^ re Co ~ 3 3* re re 3 i i ■ o a a* i .»• re _ 3" ~ _ ~. a. re a a -. >S ^ re 2; i a •« r- Si 3 a re co :;• s"** e» 5. - ? ~ ~. a 2 ~ ~ •»» — re tn S. a- a. b C1 a co -a S.S $■8-00.3 re J a i re i a re re ^« .*• » re ST § 5' LUTHER BURBANK And it was a fruit of a new order — neither apricot nor plum. In view of its origin, it seemed appropriate to christen the new fruit the Plumcot. Parental Resemblances The new fruit is similar to the plum in its firmness and color. In form also the cross usually follows the plum parentage, for every shape that is seen among the many thousands of varieties of plums is also seen among the plumcot seedlings. But there are varieties also that closely resemble the apricot in form. The stones vary widely, some of them almost duplicating the apricot stone, and others being similar to the plum stone. A few varieties have stones which resemble the peach stone in many respects, especially in the corrugated and honey- combed appearance and in thickness of the shell. There is no uniformity in the color of the stones. Some of them are almost white, others yellow; a few are wine colored; and there are browns of various shades. The sharp, knife-like projection from one edge of the stone — a characteristic of the apricot — is found in many of the seeds of the plumcot. Notwithstanding these extreme variations, however, it is usually not difficult to distinguish between the plumcot seeds and those of the plum or apricot. They are usually plumper than those [284] Sj'-ii 2 SB3 a a a* re ~ *■* ,:::a § 3 S "a tc 5" SS.a5' **= S re a ** -.&*■" S £.0* re's -"a Q p a re a -> 2 a- ?i-«?^? re a 5 a\*§ 5 re O 2-re «•- l ^'^ a * «3> re ~- 1 "» >>j tLa^a* re re n 2 „»J 2. £ 5 » «, g- 3 a re I2 - ,™ ; «i s « t ." * JTSre ^* p* CC *■■ c ~ re a ■ a -" E 2 a. i «» o o 3 i LUTHER BURBANK of the plum, and have an individual appearance that would be noticed by anyone who examines them. Some stones are attached to the flesh, while others are free, some are smaller than the stones of either the plum or apricot, while some are much larger, comparable to the peach stone. The flesh of the new fruit is — the flesh of a Plumcot. As great production as could be desired, com- bined with large size and other good qualities, had not up to that time been produced. This lack, while discouraging for the time, was by no means an insurmountable obstacle to the production of a fruit comparable in its relative perfection to our other standard fruits. When it is possible to add to the most stubborn plant, practically any desired element — color, hardiness, earliness, or any other it may lack — the plant improver may be assured that productive- ness can also be added. In order to give an idea how a number of seedling plumcots proved up, the following test records of some of the plumcots produced are listed. It is to be remembered that these are some of the results of earlier experiments. On consulting my record books, I find that the earlier Plumcots were usually listed as poor to [286] LUTHER BURBANK medium growers, and almost without exception as poor bearers. Such records as these are typical: "No. 10 — Poor grower; fruit small. No. 14 — Strong grower and poor bearer. No. 16 — Poor grower and poor bearer. No. 18 — Medium grower and poor bearer." This is not as discouraging as it might seem on the face of it. All of the trees represented by the above numbers bore regularly; they produced a fair crop every year. Moreover, there were others that were listed as "medium" bearers, and even as "heavy" bearers. One of these now fruiting produces such an enormous quantity of fruit that it would seem im- possible for the tree to hold it; the branches are literally crowded with plumcots from base to tip. Quality also is good. So this variety gives a good basis for more seedlings and for crosses that will produce regular and abundant bearers of fruit of superior quality. The plumcot was at first slow of improvement owing to the comparatively few seeds available, and the time it took those to come again to bear- ing, yet a number of varieties which combine the pleasing quality of the apricot with the hardiness and productivity of the plum are already in existence. The larger proportion of the successful crosses [288] 1 a a *l*e*l£l •*:ir* 2 So 3 g,» « _"o ^. ft« u l^ »^i '■•^3 **- n ^-. Ob sis? ^g^5-=a ' Q 2. O ft O § « :>» S 3 ft •rn i to f^ 2 §"o 8 3 1 7 n ' a a. LUTHER BURBANK between the apricot and the plum have been made with the Japanese plums. Few seedlings have been raised from the apricot trees pollenized with the Japanese pollen, the seeds generally being produced on the plum tree. The seedlings of the second generation show an astonishing number of variations. Although both trees and fruits of these variations usually resemble both parents in various respects, yet we are so unaccustomed to seeing such combinations of characters that they appear to be new. In fact, the combinations are new, though the characters exist in the heredity of one parent or the other; but these are often greatly intensified in certain individuals. Further Characteristics of Tree and Fruit The foliage, growth and general appearance of the plumcot trees most often combine the charac- ters of the two species in such a way that it is impossible to classify them either as plums or apricots. There are, of course, many gradations, so that some trees much resemble the plum, while others closely resemble the apricot. Several varieties of the new plumcots were exhibited at the Pan-American Exposition at Buf- falo in 1901. The exhibit aroused interest — both for its novelty and beauty and because of its prom- ise of a new fruit for the orchardist. [290] §£ a. •a - £."* a 5 rt ?* to 3 ?? J? j ' ™ ~ a "als.1 n « S '» § 3^§ Sj« iL r* ft £: s-x. <» s _ 2 ft ~ 0,"* 1 S ' 5 g 2S2 ft a C » rt a, 5: S&-S.I -» S- ft « a 0 a H "a c« c ft O ~» H JS*s» a-*1 a, ft C ft a - 2. a,*i a* ft x. c 1 c a Si!"* Ill >-> CO 00 LUTHER BURBANK As announced in The California Fruit Grower of May 24, 1903, a special gold medal was struck as an award — though no award had been sched- uled, or could have been for any such exhibit. Such fruit had probably never been thought of by the board of awards or any one else. Such recognition was pleasing. Yet the plum- cot in 1901 was far from being a perfect fruit. It was rather in the experimental stage. Further work in cross-breeding and selection was requisite for its perfecting. The first one of these plumcots introduced was sold to John M. Rutland of Australia. Mr. Rutland came from Kiewa, Australia, and lived near my Sebastopol proving grounds for several years in order to study these new fruits, as well as the cactus and other of my productions. When he saw this plumcot, he thought it good enough for introduction. Accordingly, in July, 1905, he purchased the right of distribution in the Southern Hemisphere, including all of Africa. He named this variety the Rutland. The following year the new fruit was intro- duced in the Northern Hemisphere by George C. Roeding of Fresno, California. The Rutland has long, slender branches and long, slender leaves. It is a completely balanced combination of the Satsuma plum and the apricot. [292] Cherry Plumcot This beautiful fruit is a curious combination. The fruit itself is a true plumcot, whereas the stem and leaves are dis- tinctively those of the plum. The coloring and dotting of the skin are characters that reveal the plum parentage; but the other qualities of the fruit are closely suggestive of the apricot. LUTHER BURBANK The exact pedigree of the Rutland is inferred rather than known. The crosses were so numer- ous and so complicated at that time, that no at- tempt was made to keep an exact record of all of them. There is little doubt, however, that Sat- suma is one of the parents, because the flesh of the Rutland is red, and the Satsuma was the only plum which had red flesh that I was using for crossing at that time. The fruit of the Rutland is large, globular, cling-stone; both the flesh and the skin are of a deep crimson color. The flesh has an acid flavor until mature, and when fully ripe resembles the Satsuma in its acid qualities. Its principal value is for jam and jellies. There are a dozen or more bearing trees of this variety on the Sebastopol place, and they have never failed to produce a crop each season. The amount of fruit, however, is too small to make the trees valuable commer- cially in this climate. The Rutland was a fruit of unusual scientific interest, and was introduced partly under that consideration — not merely as a commercial fruit. It was sent out as a curiosity, the type specimen of a new kind of fruit and the forerunner of numer- ous good varieties that will follow. Fixity of the New Species It might be thought that seedlings from plum- [294] ON THE PLUMCOT cots would revert to the type of plum or of apricot, but they do not. The combination is complete and permanent. Among the many thousands of seed- lings which have been grown, not one has pro- duced either true plum or true apricot. All are plumcots. It is therefore plain that the new fruit is fixed as a species. Of course it is not expected to fix any of the varieties so that they will come true to seed, any more than any variety of plum or apple or pear will come true to seed. Nevertheless, the mixed heritage of the new fruit is not altogether obscured. The tendency to segregation of plum factors and apricot factors in the second and succeeding generation is variously manifested. It would probably be feasible to se- lect specimens that by inbreeding and selection could be made to develop races fairly duplicating each of the parental stocks. Such an experiment would have scientific interest rather than practical value. The plumcots are still new; they have not been introduced to the general trade long enough to be fully tested in many parts of the world. It was hoped from the outset that among the new varie- ties some would be found bearing fruits equal to or better than the apricot in flavor, on trees at least as hardy as the standard varieties of plums. [295] LUTHER BURBANK This expectation has been realized in a variety of plumcot that has been named the Apex. This makes it possible to raise delicious apri- cot-like fruits in many localities where the apricot cannot be grown. The Best of the Plumcots — Up To Date The best of the plumcots so far produced is that just mentioned, the Apex, a final selection in 1911. It ripens with the very earliest of the early plums, about June 10. This means that its season is about three weeks earlier inland. It has not been fruited sufficiently long in other localities to know how it will yield elsewhere. The tree is a strong, upright grower, and has never failed to bear a full crop, even where apri- cots are failures. In some cases the Apex has borne a full crop of fruit even when the plums were a short crop on account of unusual weather conditions. This fruiting capacity is unusual in plumcots of such superior quality, and marks the beginning of a new race of plumcots as productive as the plum and as valuable as the apricot. The fruit of the Apex is extremely handsome, and very large for an early fruit, being 5% to 6 inches in circumference. It is globular, and pink, or light crimson in color. The flesh is honey yel- low, firm, rich, aromatic, resembling that of the apricot, and sweet and delicious to the taste. [296] Plumcot Seedling Cluster At first glance this direct color photograph print might be taken for a cluster of Japan plums, but the finely serrated apricot leaf shows it to be a plumcot. Perhaps the most striking characteristic of this particular variety is its abundant bearing; and this is a matter of great importance, as many of the apricots have been rather shy bearers, and Mr. Burbank is working with particular refer- ence to improvement in this direction. LUTHER BURBANK The Apex tree is a much stronger grower than the Rutland, and produces perhaps ten times as much fruit. The fruit is larger and much earlier. It has yellow flesh instead of crimson, making it one of the most valuable market varieties. The Apex resembles the apricot very decidedly in form, size, and quality of fruit, while it is more like the plum in foliage, upright growth, produc- tiveness, and smooth-skinned fruit. It thus illus- trates the tendency to segregation of unit charac- ters along Mendelian lines to which reference has been made. The Apex is the only plumcot yet introduced which has promise of becoming a standard market variety, though there are others equal or superior to it to follow. Its ability to withstand the require- ments of long shipping have not been thoroughly tested, but its firm flesh and tendency to ripen slowly are strong indications of its value for trans- continental shipment. The exact parentage of the Apex is not known. The crosses have been so extensive and compli- cated that a complete record was thought of less value than the production of a fruit that would feed the millions. It is certain, however, that the Apex, like the Rutland, carries blood of the Japanese type of plum combined with that of the apricot. [298] ON THE PLUMCOT The Triumph plumcot was introduced by my- self in 1911, having been, like the Apex, previously tested for several years. It is fairly productive here, the fruit ripening about August 1. It is of apricot form, is six inches around, with velvety purple skin, thickly dotted and mottled with scarlet. The flesh is firm and apricot-like in tex- ture. It is not so promising as a shipping fruit as the Apex because of its deep crimson flesh and lateness of ripening. The Triumph is primarily a home fruit, and is valuable because of unique combinations of the apricot and plum qualities. During the several years this variety has borne fruit, the trees have never failed to bear at least a medium crop. Another plumcot introduced at the same time as the Triumph is known as the Corona. It is a strong, upright growing tree, bearing beautiful, large, golden-yellow fruit with a velvety skin. The fruit usually develops a red cheek when perfectly ripe. It is firm, sweet or subacid, and delicious. The Corona is a cling-stone. It ripens July 25. It is an unusually rapid-growing tree, but it is not so productive as the Apex. It will probably be grown only for home use. It is possibly hardy enough to be grown in many localities where the apricot does not fruit, and may be appreciated [299] LUTHER BURBANK there because of its resemblance to the apricot. Besides the varieties that have been introduced, I have some thirty other selected varieties that have been given temporary names, for further testing. Some of these will doubtless be intro- duced if, as expected, they prove of value. Hundreds of other seedlings are being tested but have not developed sufficiently to give a very definite idea of their qualities. Hybridizing the Plumcot Now that the plumcot race has been thoroughly established, it is necessary to make further crosses. The obvious way to obtain improved varieties is to cross the best seedlings of those already pro- duced. This is being done every year. Seeds of all of the plumcots grown on my place in 1912 were saved and planted; possibly two thousand of these seedlings being grown. One of my named varieties that has not been introduced is perhaps the most prolific fruit tree ever produced. The seeds from this are being saved separately. It is probable that the seedlings grown from this variety will be remarkable producers. By crossing some of the plumcots with the Pru- nus pissardii plum, some purple leaved plumcots have been secured. This characteristic of dark foli- age is readily transmitted in the plumcot cross as [300] 2 ° 5*2. 2.2 5 2 3**53 55 5 © •» — to-|5is © 3 c -.£ ~. ft ■* S31 "8 3— 2 2 o. c 5 "i *S 3 w » r i i «• si" 22"o S. n ft « a O © O a c « * 2. a «"o ill n «= « -» <* "a oca 33SH ft ■* s • Co O.X: . ~. n 2.5" ~2o ~. C E <» n Tl m © 9 «•'«»£ a a*a- o* * ft "S.3 2! A a* O 2 5* ft 2 i a 3 © n a- LUTHER BURBANK it is in the plum crosses. It is expected that by this cross one or more varieties of plumcots will be secured that are valuable both for fruit and foliage. The purple-leaved plum trees have proved of great value for decorating lawns, and the plumcot trees are considered of even more value by some, because of the unique combination, and the bril- liant color of the foliage. From a study of the plumcots already pro- duced, it is safe to say that this new fruit will become known and grown in all climates where deciduous fruits are found. Numerous improve- ments must be made before the plumcot will become as popular as either of its parents. But only time and patient selection are required to effect these improvements. It is quite possible that in many regions the plumcot may in time replace the apricot as well as many of the plums. But more important by far than the quality of the plumcot as an orchard fruit is the lesson it has taught as to the possibility of producing new fruits by hybridization. The plumcot stands as the first addition to the list of orchard fruits that has been developed within historical times. Apples, pears, plums, peaches, cherries, apricots, quinces — all were [302] *B S-5 ^ ft ^i^S "SI o 5 « "« 5 a. "a n 3 ft ft q, <— . 2. 3 5. « "2. 1 s* £• 3' 5* a •ft 2. «5 £• 3 2 >2 1 ft "r 3 "£ ^ en « ■-* a ft a » 2 ft _ :;• ~i F ft' 2 ~ ft _ *» "b to r\ to r\ m *■* >• ft ™ — ft © £ O ft ~» ft E • «.- a fe o 3 - © ~ to J| ft ft fcf j ft* © -.3 W (y B ft o ^ft^ S~^ 3 5' ft © 5 o "a ^. -1 n> . 3" 1 § ? 2 •o ft "a fig ft 3*« a- I a" * ft 30S R 2 o o 09 O «•» © OS LUTHER BURBANK known to the Romans and Greeks and to their forbears of Oriental antiquity. The plumcot is a new species that originated just at the close of the 19th century. Its production forecasts a new JX%ijtf*^riu£V>^ development. \&\* %<& [End of VoLUME^Uf'* — Plant improvement of any kind tests purse and pa- tience; at every stage of the work shortcuts must be intro- duced in order that time and expense may be saved. List of Direct Color Photograph Prints in Volume V Apricots Page Siberian Apricot 274 Plums A Basket of Plums Frontispiece The Blood Plum of Satsuma C A Typical Chinese Plum It Typical Satsuma Plum Tree 13 The Fruit of the Burbank Plum 17 The Tree of the Burbank Plum 19 Crossed Plums 23 An Early Burbank-Satsuma Cross 25 The Prize Plum 27 The Sultan Plum 31 The Sultan Plum Tree 33 A Burbank-Satsuma Plum of 1913 35 The Lieb Plum 37 Plums of Chinese, Korean, and Siberian Types 41 Typical American Wild Plums 43 The Giant Maritima 47 The Late Shipper 51 A Kelsey-Satsuma Hybrid 55 Jordan Plum Fruits 57 Tri-Parental Seedlings 59 The Challenge Plum 61 Santa Rosa Plum 65 Formosa Plum Fruits 67 Formosa Plum Tree in Bloom 69 Beauty Plum Fruits 73 The Wickson Plum 75 A Wickson Hybrid 77 One of the First Stoneless Plums 138 A Curious Fruit 143 Not So Good as They Look 147 Stoneless Anomalies 151 Small but Luscious 153 Large and Luscious 155 LIST OF ILLUSTRATIONS (Continued) Page Striking Contrasts 159 Stoneless but Unmarketable 161 Absolutely Stoneless 163 Tbe Gee Wbiz Plum in Bloom 166 An Ideal Plum Tree 171 Spur Bearing 173 Skin Texture 175 A Practically Perfect Plum Tree 177 Ideal Foliage 179 Protective Foliage 181 Foliage Protection Further Illustrated 183 An Ideal Root System 185 Progressive Ripening 187 Ideal Form and Bloom 189 Ideal Form with Flesh to Match 191 An Example of Even Bipening 193 Seedling Red Leaved Plum 196 The Egg Bartlett Plum 201 June 25th Plum Fruits 205 "Three-String" Plum Fruit 209 The Apple Plum 213 Another View of the Apple Plum 217 Firm, Sweet Plum Fruits 221 Globe Plum Fruits 225 Early Crimson Plum Fruits 229 The Home Chestnut Plum 233 The Turkey Egg Plum 237 The Bully Plum 241 Big and Handsome but Nameless 245 Typical Wild Worthless Plum Seedling 249 Small, Poor Foliage 253 Mosaic Variation 255 Foliage of Fair Promise 257 Typical Good Bearer 259 Typical Good Purple Leaf Plum 261 Purple Leaved Plum with Fruit 263 A Diseased Specimen 265 A Weakling 267 Leaves Showing Mixed Inheritance 269 A Tree of Vigor 271 Plumcots A Faulty Beauty 63 The Odd Plumcot 277 Sweet Plumcot 281 Intermediate Form of Plumcot 283 Plum-Like Plumcot 285 The Abundance Plumcot 287 A Superior Plumcot 289 The Best Plumcot 291 Cherry Plumcot 293 Plumcot Seedling Cluster 297 The Plumcot Called the Burbank 301 Cluster of Apex Plumcots 363 LIST OF ILLUSTRATIONS (Continued) Prunes Prune D'Agen Fruit , Pa|l The Giant Prune and Its Parents 85 A Veritable Giant 87 The Giant Prune on the Branch 89 Prunes Drying on the Tree ...!!! 95 Prune Tree in Blossom. 99 Thinning a Prune Tree " 101 A Typical Prune Cluster Before Thinning. 104 Prune Cluster After First Thinning 105 Prune Drying in California [ 108 Fruit of the Splendor Prune \\[ ' j10 Splendor Prune Graft in Blossom 113 Fruits of the Sugar Prune . 117 The Standard Prune ]]] ' ' -(23 Sugar Prunes and Standard Prunes Compared...!..!..... 125 The First Stoneless Prune \ 129 Success at Last '.'.'.'.'. ' 131 The Conquest and Its Parents 133 Stoneless Beauties 135 fKoemrr library H. C. State College Mwrcrrr i»«A*r flw C. State Colleg*