6 810247800 I9ZLI wl OLNOWOL dO A ene Sa as aie pT es pin ea Mie Rey Soe bain HOW PLANTS ARE TRAINED TO WORK FOR MAN BY LUTHER BURBANK Sc.D x GRAFTING AND BUDDING VOLUME II IK Cf foe qe KE Gil EIGHT VOLUMES ~° ILLUSTRATED PREFATORY NOTE BY DAVID STARR JORDAN P. F. COLLIER & SON COMPANY NEW YORK CONTENTS THe Fragrant CALia THe STONELEsSs PLUM THE Roya WALNUT . THe WINTER RHUBARB THe BurBank CHERRY THe Sucar PRUNE Some INTERESTING FAILURES PLANNING A NEw PLant PLANT AFFINITIES . Practical PoLLINATION QUANTITY PRODUCTION GRAFTING AND BuDDING LeETTIne THE Bets Do THEIR Work 1 Vol. 2—Bur. A LIST OF ILLUSTRATIONS Tue Fracrant Catta . . Frontispiece PAGE THe Spaprx oF ONE oF THE CALLA Ae i Seer pinay ona een ha Wel were ay > - DO CRASS eet, es a STRAWBERRIES SHOWING VARIATION 2 A Tyricat Stonetess Plum... 88 DovuBLE SEEDS SoMETIMES TAKE THE Piss OF Ai STONE 2. (62 oe Se THe ORIGINAL AND THE FINISHED MmEOOUC?. § iar Bote oe 8 OG ae A SrxTeen-YeEAr-OLD “Roya” WaLNuT- 62 Woop oF THE “Royat” Walnut . .. 66 “Paradox” WaLtnut Woop Two INcHES tN Diameter Eaco YEakR . . . 70 VARIATION IN Hysrip WALNUT LEAVES . 76 3 4 LIST OF ILLUSTRATIONS Hysaew Wa.Nvuts ey A Grarren WaLnut TREE .. . A Typica, Piant or Giant Worms Ruvomage . . se te Beapy von Surpmuwr |... YF Tue Giant CHeRRy . . . =. .; Tue Asunpance CuErry THe Sucar Prune and Its PaReNTs . | A Luscious Faurr. .. . ae - Porato Sxzp Batis «ks. «94 ae Leaves or STRAWBERRY-Raspserny Hy- BRIDS . . >. ~ . . . Lge eo Comp ete Kir or Potienizixe Toors . ONE OF THE OriIeNTAL PEARS AMERICAN Pears witH BLENDED Herep- _ITIES . . . . . — . *. am ‘Tew Conn VaRniaTIONS . is Wee Corn Trosinte Hysrits SEVENTEEN FEET HiexH . LIST OF ILLUSTRATIONS Corn SELF- POLLINATED AND CROSSED WITH TEOSINTE Some STEMS OF BLACKBERRY-RASPBERRY Hyeprips A SHIRLEY Poppy—SHowIne REPRODUC- TIVE ORGANS PoLLEN-BeEarIne PumPxin BLossom SrED-BEarInc PuMPKIN BLossom A PoLLEN-BEARING GRAPEVINE . STRAWBERRY Bossom (ENLARGED) THe STIGMATIC SURFACE OF A Poppy Mucu ENLARGED Cross SECTION OF THE CacTus BLOssom RASPBERRY BusH AFTER POLLINATION . “Fiat” witH LAYER oF GRAVEL “Fiat Partiy FILLED witTH PREPARED Compost A CoLtp FRAME PROTECTING SEEDLINGS FROM THE BIRDs Younc PLaNts AWAITING SELECTION 6 LIST OF ILLUSTRATIONS — CompLeTe Grartine Ovrrir . Currine Srock ror WuiP Grart . A Smwe Grart is Postrioxn . Crown on Bark Grarr . . . . Curmmc tHe Bark to Receve A Bup : Tue Bup Grarr ComPpLerep Reapy ror SHIPMENT A Hysrew Evercrren + ee ‘€882 2281 THE FRAGRANT CALLA How Fracrance Was INsTILLepD IN A SCENTLESS FLOWER OT long ago a young woman visitor who \ had learned that the function of odor in flowers is to attract bees and other insects made a remark at once naive and wise. *Tt seems wonderful,” she said, “that bees and other insects generally have the same tastes in color and perfumes that we human beings have. The rose and the apple blossom are sweet to them as well as to us; whereas one might expect that they would care for something quite different, especially when we remember that cultivated people generally like more delicate perfumes than those that please uncultivated people.” This remark, as I said, was at once wise and naive. It was wise because it showed a tendency to seek causes for things in nature instead of taking them for granted as most people are prone to do. 7 5 LUTHER BURBANK — It was naive because it quite overlooked the true significance of the function of odors to please or displease man, but to please and attract the insect. ae And man learned to like the odors that were constantly presented to him largely because they were constantly presented; just as you may learn to like a food—say, for example, olives—by repeatedly tasting it, though at first you do not eare for it. | 2 The exception, of course, is the odor that is associated with unhygienic things, such as decaying vegetable and animal matter. These are attractive to the insects that feed on them — because the substances that produce the odors are to these insects wholesome. But they do not attract the bee because they contain nothing on THE FRAGRANT CALLA 9 But doubtless the carrion beetle finds the odor of decayed meat a much more attractive aroma than the odor of orange blossoms. And, to make direct application to the case in hand, unquestionably the flies and other insects that are useful to the calla in pollenizing its flowers would be quite unattracted by the sweet and pervasive odor that is given out by the new race of fragrant callas which I am about to describe. _ How THE Catia Is FERTILIZED It was on inhaling the perfume of my fragrant calla that the visitor made the remark I have quoted. And she followed it with this question: “Tf the odor of plants is of use to them in attracting bees, why do not all the callas have a perfume like this new one you have developed?” And here again a moment’s reflection would perhaps have supplied the answer. The calla does not need to attract the bee, therefore the production of the chemical substances that give out a sweet perfume would have been a waste of energy for this flower. Perhaps there may have been a time in the past when the calla, like so many other flowers, depended on bees for cross- fertilization, and lured them with its odor; but nowadays the process of cross-fertilization in this plant is effected in a quite different fashion. 10 LUTHER BURBANK If you closely examine the calla you will observe that what you would casually speak of as a single blossom is in reality @ case or — shield—in point of fact a modified leaf— twisted into a sort of cornucopia and adjusted about a central stalk or “spadix” on which many minute and inconspeunse aia clustered. The object of this Artengenuish senile in part to give protection to the flowers, but largely to supply a conspicuous signal to attract sight roving inessts) in petligee of small gnats and flies. —_- In point of fact the white conigiy lt tin alia effords 9 very convention’ (phee at ane numerous small insects. Testa have shown that the air inside sheila “blossom,” particularly toward its base, where the insects congregate, is perceptibly warmet than the outside air. It has been proved by recént experiments that the chemical processes associated with plant — growth generate heat. Germinating seeds, for example, give out a measurable quantity of heat. So it is not strange, perhaps, that the partially confined air at the base of the tubular calla flower case is at all times a little warmer than the surrounding atmosphere. THE FRAGRANT CALLA il In any event the insects find this a snug corner, the attractiveness of which is further enhanced by the presence of a certain amount of edible pollen, In short, for such insect tribes as like the particular fare which the calla offers, its beautiful white tube constitutes a highly attraetive lodging place and lunchroom. Meantime, while the insects are lodging at the base of the stalk on which the true flowers grow, these flowers shed their pollen and let it settle on the backs of the visitors. And when, in due course, the inseets resume their voyaging, they carry the pollen with them and in time transport it to other calla blossoms; for when they enter the new flower they are likely to find the stalk at its center a convenient -alighting place, and crawling down this are sure to leave some of the pollen in contact with receptive pistils. That the pistils shall be those of a different plant from the one that supplied the pollen is insured by nature’s familiar device of having the stamens and pistils of the same flower ripen at different times. A Gtrt or NATURE All this sufficiently explains the utility of the large white modified leaf or spathe which we THE SPADIX OF ONE OF THE CALLA LILIES . From this direct-color tb it will be soon, thet the coat ane within the lily, called the spadix, is in ite fact a composite flower itself, on which — many minute and inconspicuous blos-— soms are clustered. Both these stami- nate blossoms and pollen grains at the ex top, and the pistillate ones lower down, may be clearly seen. THE FRAGRANT CALLA 13 commonly speak of as the calla’s flower, and also the normal habit of this flower in producing only the musty odor which is rather disagreeable to us, but which is obviously attractive to the particular insects which the calla needs as coad- jutors. But it does not explain how it chanced that among a large quantity of seedlings of a tribe of calla, known as the “Little Gem,” I one day found a single specimen that not only lacked the disagreeable smell of the others, but had a mild yet unmistakable aroma that was distinctly pleasing. Explanations aside, such a specimen did appear among my callas, and it was by raising seedlings from this anomalous specimen and carefully selecting the best specimens for succes- sive generations that I developed the perfumed calla. The first plants that grew in the first gener- ation from seeds of the first fragrant calla showed no improvement over their parent in point of fragrance. But in the second gener- ation, as so often happens, there was a marked tendency to variation, and from among the numerous seedlings of this generation I was able to select one that had a fully developed and really delightful perfume. 14 LUTHER BURBANK | By propagating this specimen as usual, by division, fragrant callas precisely like the the mother plant were soon developed i in wee from the seed, draplepetngy ye varieties ever equaled the selected plant, and the finest fragrant callas in existence to-day are all the descendants, through the process of division, of the original second generation seedling. This mew. race of .collas -waacmemed tie Tur New Caria a “Sport” It thus appears that the perfumed calla was developed through selection, and in the short period of two generations, from a individual that appeared “spontaneously” among some thousands of odorless seedlings. . Using a term that is peculiarly populat. in recent years, we might say that so marked a variation from the normal or usual form of calla constituted a “mutation.” Hi THE FRAGRANT CALLA 15 In the size and color and general appearance of its flower, as well as of its entire structure, the new calla precisely resembles its fellows, Yet we are surely justified in speaking of so very marked an anomaly as the production of a strong perfume as constituting an important departure from the normal. No one knows precisely what the chemical changes are that produce the perfume of a flower, or through precisely what transmutation of forces one flower is made to produce an odor quite different from the odor of other flowers. But for that matter no one knows just what are the conditions that induce the stimulus that we interpret as an odor of any kind. The sense of smell seems the most mysterious of our senses. But whatever these inherent conditions may be, they constitute changes in the intimate structure of the plant itself that must be ad- mitted to be important in character, inasmuch as they have to do with the well-being of the plant, and may even determine—through their appeal or lack of appeal to insects—the perpetuation or _ the elimination of a species. In the case of the scented calla it was perfume that differentiated a particular individual from thousands of other individuals growing in the same plot. 16 LUTHER BURBANK © flower, put it in a plot by itself, gave it every encouragement, and determined that its progeny should live and perpetuate the particular strain it represented; whereas but for this single feature of variation, that individual plant would in all probability have been destroyed along with hundreds of others. The development of the fragrant calla, then, through artificial selection based on the recog- nition of the value of fragrance as an addition to the attractiveness of this flower, represents in a small way and in epitome the history of the development of numberless races in nature. through the operation of natural selection. , In this particular case, natural selection prob- ably would not have resulted in the production of a race of fragrant callas, because, as already pointed out, fragrance of this character has no value for this particular flower. It might even chance that the fragrance which to our senses is exquisite would prove unattractive or even repellent to the flies that normally frequent the spathe of the calla and aid it in perpetuating. its species. In that case natural selection would cestalely insure the early destruction of the race of fra- grant callas. It may well have been through such THE FRAGRANT CALLA 17 discriminative selection on the part of insects that the calla lost its scent in the past ages. For of course natural selection can operate even more effectively in weeding out organisms that have undesirable traits as in perpetuating organisms that show favorable variations. One process is necessarily complementary to the other; they are two sides of the same shield. . In another connection we shall have occasion to deal more at length with the processes of natural selection; and we shall see numberless examples before we are through of the way in which artificial selection is instrumental in de- veloping new races of plants. FouNDATIONS OF NATURAL SELECTION But for the moment I will consider a little more at length the question of the origin of the variation which resulted in giving this particular calla a perfume that was not normal to its race. In so doing, we shall gain a clue to the genesis of other types of variation or mutation through which various and sundry new races of cultivated plants have originated, and through which also, we have every reason to believe, numberless spe- cies of animals and plants in a state of nature have been evolved. HYBRID CALLAS _ A glance at a few of the curious combinations and variations which ap- pear after crossing the various species. — Some of the new Callas are of gigantic size, whereas others bear flowers only an inch and a half across. ee a a ee ae a. poe ga ee eM ee et < cM R igen OP ne a tae Re ee THE FRAGRANT CALLA 19 The presentation of this subject puts us in touch with one of the newest and doubtless one of the most important aspects of the problem of, evolution. Since Darwin we have fully understood that all evolution of organic forms must have its ori- gin in variations. No two individuals even of the same species are precisely alike, and it is not at all unusual to find individuals of a species showing very considerable differences, even as regards the essentials of size and form and function. Indeed, a certain range of such variations is considered to be absolutely normal. | One would never state, for example, that any particular bird has a wing or beak or tail of precisely a given length; instead of this the _ ornithologist records the average or mean length, or the limits of variation shown by different specimens. And it is universally recognized, since Darwin gave us the clue, that the building up of new species must be brought about through the selec- tion of favorable variations. A bird with an extra long wing, for example, might be able to fly a little faster and secure its insect prey with greater facility than its fellows; and this slight advantage might be instrumental in saving the life of such a bird, and thus enable it to transmit its peculiarity 20 LUTHER BURBANK to off spring that would constitute a long-winged, swift-flying race. Take the following incident as a tangite illus- tration. In the summer of 1904 it chanced that there was a severe drought in New England and there were entire regions in which the insects upon which the common house martin feeds failed to be hatched at the usual time. The result was that there was dearth of food for the martins, and a very large proportion of these birds died of starvation. In some cases forty or fifty birds would be found starved to death in a single bird house. __ There are entire regions in New England to- day where the martin is a rare or unknown bird, although prior to 1904 it was abundant. Now, we may reasonably assume that any in- dividual martins that escaped were those that had either greater powers of flight or a stronger inherent tendency to make wide flights in search of food than their fellows. The few individuals thus saved furnish us a concrete example of the survival of the fittest through natural selection. And this illustration is cited at length because it makes tangible the fact, to which I shall have occasion to revert time and again, that the proc- esses of nature through which species have been THE FRAGRANT CALLA 21 developed in the past are still in operation every- where about us. Many people are disposed to think of natural selection as a principle referring to past times and to the development of organ- isms long since perfected. In point of fact past times are like present times in the operation of their laws. The re- actions between organism and environment are now what they always were. No race is perfected, no organism freed from the struggle for exis- tence; although, of course, under the conditions of civilization the operation of “natural selection” may be modified through man’s influence, and the conditions of life for a given organism radically changed by artificial selection. Evo.LutTion THroucH MutTAatTIon But let us not forget our theme. With the case of the fragrant calla to furnish our text, I was about to speak of those variations from the normal on the part of any given organism which lie outside the ordinary range of variation and which therefore constitute so definite and pro- nounced a departure that they have long been spoken of as “sports.” To these some of the present-day evolutionists, following Professor Hugo de Vries, give the name of “mutations.” 22 LUTHER BURBANK | It has already been said that the appearance of a fragrant calla constitutes such a change. But of course the anomalies that are usually listed as mutations are often of an even more noticeable character. A classical illustration was given by Darwin himself in the case of the Ancon ram, which was born with legs only half the normal length, and from the progeny of which wes developed a short-legged race of sheep. _ But the word mutation had not come inta vogue in Darwin’s time, and the idea of evolution through such marked departures from the normal was subordinated in Darwin’s interpretation of the origin of species, or at least in that of his immediate followers, to the idea of advance through the preservation of slight variations. So when, just at the close of the nineteenth century, Professor Hugo de Vries came forward with his “mutation theory,” it had all the force of a new doctrine, and was even thought by some enthusiasts—though not by its originator—to be in conflict with the chief Darwinian doctrines. The observations that led Professor de Vries to the development of this theory were made on a familiar American plant that had found its way to Europe and was growing in profusion by the roadside near Amsterdam. The plant is known as the evening primrose. THE FRAGRANT CALLA 23 Professor de Vries noted a hitherto unde- scribed variety of this plant in a field near Amsterdam. He took specimens of the plant to his experimental gardens and carefully watched the development of successive genera- tions of seedlings. . To his astonishment he produced in the course of a few generations more than a dozen divergent types of evening primrose, all descended from the original plant, each of which bréd true to the new form suddenly assumed. Professor de Vries spoke of these sudden and wide variations from type on the part of his evening primrose as con- stituting “mutations.” He conceived the idea that similar mutations or sudden wide variations had probably consti- tuted the material on which natural selection had worked in the past. Such mutations being ob- served to occur in the case of the evening prim- rose, it is not unnatural to argue that similar mutations might occur in the case of other organ- isms; and it requires no argument to show that such wide variations offer better material for the operation of the laws of natural selection than could be offered by the minute and inconspicuous variations that had hitherto been supposed to mostly constitute the basis of evolutionary changes. 24 LUTHER BURBANK | There were many reasons why the mutation theory appealed to contemporary biologists, thus accounting for its very cordial reception. “a For example, there are numberless instances in nature where the development of a useful organ is exceedingly hard to explain on the basis of natural selection, because the organ in its incipient stages could have no utility. Similarly a modification in the location of an organ—say the shift in the flatfish’s eye until both eyes are on one side—is difficult to explain as a process taking place by infinitesimal stages, on the basis of natural selection. A slight shift in position of the eye of the flat- fish would have no utility whatever. It is only when the shift has become sufficient to bring the eye on the upper side of the fish that the creature would have any advantage over other flatfish whose eye is on the under side. If we imagine a mutation in which a fish appears with an eye distorted in location suffi- ciently to be usable while its owner lies flat on its side in the mud, we can readily under- stand how such a mutation might be favor- able to the individual and thus might furnish material for the development through natural selection of a race of flatfish having both eyes on one side. THE FRAGRANT CALLA 25 We have every reason to believe that the races of flatfish now existing have recently— in a geological sense—developed their observed condition of having the eyes thus located; indeed, proof of this that amounts to demonstration is furnished by the fact that the young flatfish even to this day is born with its eyes located like those of other fishes, the migration of the eye, so to speak, taking place as the individual] develops the racial habit of lying on its side. But as I said, it is unquestionably difficult to conceive how the useful distortion came about unless it began suddenly as a “sport” or muta- tion. This is one instance among many. And so Professor de Vries’s observation, which proved that mutations do sometimes seem to occur “spontaneously” in nature, was seized on as affording a solution of one of the puzzles of evolution, and the mutation theory was pretty generally regarded as a valuable supplement to the Darwinian theory of evolution. It should be clearly understood, however, that neither Professor de Vries himself nor anyone else speaking with authority, has thought of the mutation theory as in any sense contradicting the Darwinian theory of natural selection. On the contrary, it is to be regarded as supplementing and supporting that theory. If creatures are 26 LUTHER BURBANK subject to large variations in a single generation, such variations afford peculiarly good material for the operation of natural selection. Moreover, evolution by mutation would presumably be much more rapid thenssvaletiae ee for He arennge Upcs ae ee Wuat Causes Mutation? — Jncideotally the ides of relatively aaphl ove | tion, thus given plausibility, answered the objec- tion of certain geologists who had questioned whether the earth had been habitable long enough to permit the evolution of the existing forms of life through the cumuletive » series of fragmesitary pleas seas placed before him, and added: : “To make a stone grow smaller was certainly a notable feat. How did you manage it?” This is a question that has been asked more often, in connection with the stoneless plum, than in the case of almost any other of my plant pro-— ductions. For a plum which looks on the outside precisely like any other, but which is found to:he : : stoneless, never fails to excite surprise. Even visitors who know what to expect, when asked to bite through one of these specimens, can seldom refrain from exclamations of wonder when the teeth go right through the fruit as read- ily as they would through a strawberry. Many persons are not greatly interested in the daisy that combines four specific strains, because they know nothing of the difficulty of making such a union, and are quite unmoved by the spectacle of a white blackberry or a fragrant calla, because they have seen white fruits before, — and because fragrant flowers are rather the rule : | than the exception. But no one ever saw an edible stone fruit without a stone until one was produced here on my farm. So “How did you do it?” is the nihil question of laymen and scientific botanists alike on seeing this really remarkable fruit. THE STONELESS PLUM 37 And when an attempt to answer the question is made, the story seems absurdly short and simple; yet to my mind it recalls reminiscences of what was perhaps the most strenuous series of experimental efforts that I ever undertook—a quest that occupied a considerable share of my time for a period of fifteen years, and which even now is not altogether completed. As you follow the outline of this story, please recall that while it takes but a phrase to tell of the pollenizing of two plum flowers and the pro- duction of one anomaly in the first generation and of some other anomaly in the second, in reality a period of five or six years has elapsed between the pollenizing experiment and the ob- servation of the second generation results. When this is borne in mind and it is further recalled that breeding through many generations is necessary to secure the results desired, it will be clear that the production of a stoneless plum was an achievement that required its full share of patient waiting. Tue Raw MatTeRIALs At an early stage of my almost endless series of experiments in the hybridizing of plums, I chanced to hear of a so-called seedless plum that was said to grow in France, where it had been A TYPICAL STONELESS- PLUM — People are generally amazed to find i it possible to cut directly through a plum that exteriorly looks no differ- o oo ent from ordinary plums. (Note the plum at the right, offering no obstacle to the knife blade.) Some visitors are skeptical and cut cautiously into the plum expecting to encounter a stone, and are surprised to find their suspi- cions unfounded. i a a aN et Na cn 8 Lo a “ess Ao Cee a? : y ni my es RYE PEW PMOL Weeks Mee Saas neo at THE STONELESS PLUM 39 known for a long time as a curiosity. About 1890 I sent to the Transom Fréres Nurseries in France and secured grafts of this plum, which was known merely as the Sans Noyau. These were grafted on one of my plum trees, and in due course produced a crop of fruit, which, as expected, proved to be a blue-black, cranberry- sized fruit, extremely sour, soft, and unfit for eating either raw or cooked. The original shrub, as I have been informed, and as it grew here, is a rambling, thorny bush rather than a tree, utter- ly worthless for any purpose except the one for which I desired it. The fruit, besides being flavorless and unpalatable, was scanty in yield. Moreover the fruit was by no means stoneless, notwithstanding its French name. It was only partially stoneless, as most specimens produced fair-sized kernels in the fruit, and every kernel had a thick rim of stone around one side partially half covering the kernel. While it therefore lacked much of exhibiting the condition of stone- lessness that I had hoped to see, it did never- theless show a tendency to abandon the stony covering that has always characterized all the fruits of the plum family. From the outset I was convinced that by proper hybridizing and selective breeding it could be made valuable. 40 LUTHER BURBANK | The second season the blossoms of the freak plum were fertilized with the pollen of the French prune and with that of numerous other plums and prunes, , The seedlings from these crosses were to insure their earlier bearing. In the first gen- eration I obtained some plums fully twice as large as their seed parent. Most of these had stones, however, and were soft, sour fruits. A very few — of them were partially sence, ee the work was continued. Gettine Resv.ts The next generation gave some general ae provement in the growth of the tree and the size and quality of the fruit. All the seedlings of the cross from the Sans Noyau were grafted on older trees where they soon bore fruit, even though many of them showed the thorny, dwarfed, ill- shaped type of tree of the uncultivated ancestor. ) After still further selection there was a very marked tendency to improvement. In a large lot of seedlings, in 1904, I obtained two that seemed to me of favorable appearance— for much can be known from the quality of leaf and stem long before the time of fruiting. — And when, two years later, the grafts thus selected bore fruit, it was delightful to find my THE STONELESS PLUM 41 predictions verified; the fruit was almost abso- lutely stoneless, only the faintest splinter of stone occasionally appearing. And combined with this stoneless condition there were qualities of size and flavor that made the fruit practically equal to the French prune. Moreover, as is often the case with hybrids, one strain of which is wild stock, the new plum proved to be a very good bearer. , So my thought of an ideal plum having no stone about its seed was almost achieved. I say almost achieved, because there still re- mained, in the case of the plums of best quality, a fragment of shell which varied from an insig- nificant crescent about one side of the kernel to an almost complete obliteration. There were some individual plants among the numberless seed- lings that bore fruit in which the stone was absolutely eliminated, and in some cases the seed also. But it proved extremely difficult to com- bine this quality of entire stonelessness with the desirable qualities of size and _ fiavor, lacking which the fruit could have no practical value. Further hybridizing experiments, aimed at the production of an absolutely stoneless plum of fine flavor, are still under way; but in the mean- ” LUTHER BURBANK —_— time there are several varieties setuslly i Salil that are of the most admirable quality and yet wholly stoneless. In the ordinary French Preah ties $0 six pee cant’ At Aaa aaa stone; while in my stoneless prune called the “Conquest” the fragment of stone does not rep- resent more than a thousandth part of the bulk or weight of the fruit. And among the nine or ten hundred varieties — of stoneless plums now growing in my orchard, — there are sure to be some that will show still further improvement. Wuy tHe Task Was Dirricunt— The task of producing a stoneless plum had proved very difficult chiefly because it had all along been necessary to bear in mind a number of quite different objective points. It was not sufficient to produce a stoneless plum. From the practical standpoint there would be no object in that unless the fruit about ee ee ee palatable quality. And, unfortunately, there appeared to be no tendency to correlate stone- lessness with good quality of fruit. ; In point of fact the tendency was quite the other way; and, indeed, this was to be expected in view of the fact that the original partially THE STONELESS PLUM 43 stoneless plum was a small acid fruit growing on a wild bush. The problem was to combine two lines of ancestry that were in many respects directly in conflict. It would have been impossible to do this had it not proved that stonelessness and good quality of fruit, although not originally combined, have the attributes of what may be called unit characters, and hence can be assembled in a single fruit in the later generations of a hybrid progeny. THE ORIGIN OF THE STONE FRUITS A very natural question arises as to what had originally caused the little French “bullace”—as the Sans Noyau is sometimes called—to develop the extraordinary tendency to give up the stony seed covering which no other member of the family had ever been known to renounce. The question is doubly significant when we recall that some sort of shell or stony covering is almost absolutely essential to the preservation of the seeds of plants in general. The shell is often very thin, as with the seeds of most garden plants. It may be reduced to a mere filament of cellulose, as in the case of a grain of wheat. With pulpy fruits it is usually a very significant cover- ing, of which the seeds of the apple and orange afford typical examples. And with the great DOUBLE SEEDS SOMETIMES TAKE THE PLACE OF — A STONE bt In some cases the cavity left in the — plum by the removal of the stone is” wy filled by the development of a double seed. We have seen in other illustra- tions that the hereditary forces seem — to be puzzled, if this expression be — allowed, in determining how to deal — woith the altered conditions of the in- ternal structure of a fruit that lacks — the supporting stone at its center. One solution of the difficulty is shown — in this picture. hoster ¢ em ly eet Ce lines SAAN EEA AO I AN RON NE THE STONELESS PLUM 45 tribe of fruits represented by the plums, cherries, peaches, apricots, and almonds, this shell has been developed until it is veritably stonelike in texture. . It is almost self-evident why this extraordi- nary development of the protective seed covering was necessary in the case of this particular tribe of plants. It is altogether probable that the original pro- genitor of all the family of stone fruits grew in central Asia. I have received from that region a shrub that may perhaps be regarded as the pro- totype of the entire race of the stone fruits—not perhaps the direct progenitor, but an early offshoot from the ancestral stock which has remained in the original environment and has not, perhaps, very markedly changed from the original state during the hundreds of generations in which the other branches of the family were spreading southward and westward across Asia and Europe. If we could know just what the enemies of the primitive Asiatic stock of the stone fruits were like, we could perhaps surmise the reason for the development of the unusual seed cover. Perhaps the stone was necessary to protect the kernel from the teeth of monkeys or primitive 46 LUTHER BURBANK | men; perhaps it was more particularly needed as’ a protection against climatic conditions, to insure preservation during semi-Arctie winters; or to keep vitality in the kernel during protracted periods of drought, since, unlike most other fruits, the seeds will rarely germinate if fully As to all this we can only surmise. But we may have full assurance that the thick, stonelike seed cover served a useful purpose, else it would never have been developed and so persistently preserved in all the divergent races of stone fruits that were evolved under the new conditions of southwestern Asia and southern Earepe to which these fruits found their way. The roving tribes of Arabia developed a tender modified form of the fruit adapted for preserva- tion by drying, and now termed the apricot. Other people consciously or unconsciously se- lected and developed the almond; and yet others the juicy and luscious peach; while the plum ran wild and put forth a galaxy of hardy offspring that made their way to the north of Europe and also, along some now obliterated channels, to the Western Hemisphere. But each and all of these descendants main- tained, and some of them like the peach intensi- fied and elaborated, the unique characteristic of a THE STONELESS PLUM 47 hornlike or stonelike protective covering for the seed. And so, it becomes matter for wonderment that with all these uncounted generations of heredity clamoring for fruit with a stony cover- ing there should have developed in France a member of the tribe, even though it be an incon- spicuous outcast, that rebelled against the fam- ily tradition and dared to produce a seed that lacked a part of the habitual covering. How THE FREAK ORIGINATED As to just how this break with tradition came about, we can perhaps make a better guess than we can as to the precise origin of the _ tradition. It seems likely that the little bullace lost the power to produce a protective stony covering for its seed through the impoverished condition due to some defect in the condition of the soil in which it chanced to grow. Unquestionably the produc- tion of the stone makes a strong draft upon the resources of the tree. Obviously the material to supply this dense horny structure must come from the soil, and in case the exact chemicals needed are supplied in scant quantity, the shrub might be forced to economize in producing a shell for its fruit kernel, just as a hen is forced to 48 LUTHER BURBANK _ economize in the shell covering of a OE | lime is lacking in her food. The same sort of economy is practiced wien, the human child finds inadequate nourishment. In such case the bones may be not only small but defective in mineral substance, a well- type of abnormality resulting with which med- ical men are familiar. So it ‘seems: planailike thet & panei aaa food materials was the explanation of the origin of the original Sans Noyau. It is in keeping with this explanation that the Sans Noyau is, as we have seen, a small shrub, a mere dwarf as competed with anal age stature of trees of its family; and that its fruit is reduced to the proportions of a small berry, and is utterly lacking in those qualities of — sweetness and flavor that are the almost universal characteristic of other stone fruits. In a word, then, it is highly probable that the plum that supplied the character of stonelessness, _ upon which my experimental endeavors in the production of a marketable stoneless plum was founded, was a pathological product. I may add that many other “sports” or muta- tions in the vegetable world that have furnished a basis for the evolution of new races or species may very probably have had the same origin. THE STONELESS PLUM 49 Urpwiiiu WorkE This explanation of the origin of the Sans Noyau makes it easier to understand the diffi- culties that attended the progress of this experiment. Had the little plum been absolutely stoneless —so that no factor whatever bespeaking a stony fruit remained as part of its heritage—there would probably have been no very great diffi- culty in producing through hybridization a stone- less fruit of good quality in the second or third generation. All experiments seem to show that the stone condition is, as might be expected, prepotent, or, in the Mendelian phrase, dominant. So in crossing an ordinary plum with a stone- less one, it was to be expected that the offspring of the first generation would bear stone fruit. But the latent or recessive trait of stoneless- ness may be expected to reappear in a certain proportion of the offspring of the second generation; and the stoneless fruit thus pro- duced may in some cases be expected to breed true. Such is what might be expected provided one were dealing with an absolutely stoneless plum as one of the progenitors. 50 ‘LUTHER BURBANK a But unfortunately we are not dealing with an absolutely stoneless plum, but only with one in which the tendency to produce a stone has been minimized or partially suppressed. And so our relatively stoneless plum of the second genera- tion still retains traces of the hereditary propen- sity to produce the stony covering; and, as we have seen, this propensity manifests itself in the fragmentary stone, sometimes reduced to a mere © eee en thet euany of ay exhibit. Nevertheless there remains not a doubt that | from subsequent generations, from the stock in hand, an absolutely stoneless plum that — retains all the valued qualities of the fruit and in all sises, colees, and: flavess/ Geet Weare: produced. That it has been posnthle to eligniasts alee altogether, advancing thus markedly in this re- gard upon the original partially stoneless form with which the experiment began, suggests the truth of a view now held by some prominent biologists, notably by Professor William E. Castle of Harvard, that a unit character may be modified in successive generations—not merely blended or made into a mosaic with other characters, but actually modified as to its potentialities. | THE STONELESS PLUM 51 Professor Castle instances in support of this view the case of guinea pigs bred by him that developed a full-sized fourth toe on the hind foot from a rudimentary stump of a toe. The experiments just cited illustrate the oppo- site condition of causing a rudimentary organ— in this case a plum stone—io be altogether eliminated. It should not be overlooked that both experi- ments are perhaps capable of interpretation in other terms. In each case what actually happens may perhaps be better explained as reversion to a very remote ancestor. Doubtless there were among the ancestors of the guinea pig races with four toes; and doubtless if we go far enough back we should find ancestors of the plum that produced a seed having no stony covering. And we are perhaps not far wrong in assuming that it was the long-subordinated influence of this vastly remote ancestor that, in the case of my plums, sided with me, so to speak, against the forces of the more recent heredity, and made barely pos- sible the ultimate success of my hybridizing experiments. THE VALUE OF THE NEW Propuct We are so accustomed to putting up with the annoyance of the stone in the fruit that we for 52 LUTHER BURBANK the most part never give it a thought. But a moment's reflection makes it clear that the plum stone: serves men no Se ee inconvenience it gives us is obvious. 3 It requires no argument to show that a solid fruit without.« stone wauld aaaes alee acceptable. But this is not the only vessons Aims haps a sufficient one, for the development of the — stoneless fruit. The other reason looks to econ- omy of production and saving of material from — the standpoint of the tree itself. It has been — estimated that a tree requires several times as much solid material and the expenditure of far — more energy to produce the stony covering of the — fruit seed than to grow the flesh of the fruit itself. So it might well be expected that other things — being equal, a tree bearing stoneless fruit would — prove at least twice as peoaeaaes es ae i stone fruit. Under the conditions of nature, this nein fruitage would by no means compensate for the — loss of the protective stony covering, for the seed unprotected by its coat of mail would be at the mercy of any bird or animal or insect that at- tacked it. There would probably be no represenbaliis of the stone fruit family in existence to-day were it THE STONELESS PLUM 53 not for the protection afforded the seed by its hard and indigestible covering. Regardless of animate foes, the seed would perish from the effect of the sun, wind, rain, and frost, if denied protection. And this is by no means a mere matter of inference. One of the great difficulties that at- tended the experiments which I have just nar- rated was the preservation of the stoneless seeds from one generation to another. It was found to be exceedingly difficult. Various insects, es- pecially aphides, millipedes and eelworms, would get among them and quickly destroy them. Fungous diseases also attacked them. And for several years more than three-fourths of the seeds kept for planting were thus lost. At a fairly early stage of the experiment I had large quantities of seeds in hand, for I was operating on an expansive scale in order to have wide opportunity for selection. Several hundred thousand plum seeds, all stoneless, were once placed in cold storage, at freezing temperature, as soon as they were gathered and cleaned. Some were placed in sterilized sawdust, and some in charcoal dust, and some in sand. Another assortment, similarly packed, was kept in boxes in a cool shady place until the first of January, when all were planted. In both lots, 54 LUTHER BURBANK the seeds that had been kept in sand ei better condition than those preserved in the ster-— ilized redwood sawdust. Those kept in charcoal — differed little from the other lots. The ones in cold storage had suffered from blue mold more tea the others, a ee ee All were planted ‘ty thé pase iialntaeaan > by side. The seeds that had been kept in cold — storage germinated at once, and in a week were — all practically above ground. The seeds of the — other lot, which had come from the same trees, — did not commence to germinate for about six — weeks. Yet later in the season very little differ- _ ence could be seen between the two lots; on the _ ve ee : Furtuer [IMPROVEMENTS OF Mernop | An even better method of preserving the seed _ was presently developed, and I was finally able — to preserve the stoneless seeds almost as securely — as if they had their original protective covering. — My new method consists in washing the stoneless seeds in clear fresh water when first — removed from the fruit; immersing them for a — few minutes in a weak solution of “Bordeaux mixture” (sulphate of copper and limewater), THE STONELESS PLUM 55 then rinsing for a brief period in fresh water, and placing them in damp sawdust that has been sterilized by boiling, care being taken that the sawdust is barely moist, not wet. The box con- taining the seeds is placed on the north side of a building, in a cool, shady place, and examination is made from time to time to see that the seeds do not become too dry or infested with insects or mold. If treated in this way, the seeds are practically all saved; they may be planted out of doors like other plum seeds, and they will germinate promptly, , It is obvious that a seed requiring such careful treatment to preserve it all the winter would stand small chance of being able to perpetuate its kind in a state of nature. But, on the other hand, it must be admitted that it is well worth while to give the amount of attention required to the preservation of these seeds, in view of the enhanced value of their product. It will be understood, however, that the aver- age fruit grower will not be required to concern himself about the seeds, as his orchards will be propagated by grafting in case of this fruit as is customary with all orchard fruits. There can be little doubt, then, that the time is almost at hand when all our plums will be THE ORIGINAL AND THE FINISHED FRODUGE: contrast in size between the original ee of the perfected enti one o: Many generations lie between the two, yet the essential character of ate stonelessness that gave the little plan its only value has been retained in the remote descendant, while the strains of — phe numerous cultivated plums have been bred in, so that the offspring of the Ee deer} plum oe a ee - fine quality of flesh. “6 eanrthe smemen tener meer ets ~ eNO AP RR MINN RI i ae igen aie daanehl a Nils i fe be Te ‘THE STONELESS PLUM 57 grown without stones, since the experiment of removing the stones from a large number of varieties can now be followed up without great difficulty. The pioneer work has been done, and the cross breeding of my best present varieties of stoneless plums, to secure ail the desirable qualities of any existing plum, may readily be effected. | Even though the fruit should not be of better quality in other respects than that which it sup- plants, the fact that the elimination of the stone permits an increased abundance of fruit, to say nothing of the value of the stoneless fruit itself, will offer an inducement that the progressive fruit raiser will find conclusive. It should be added that the plum which has been induced to vary in the matter of seed pro- duction, is not always content merely to have cast out the stone but sometimes tends to eliminate the seed itself. Tue SEED Atso Must Go One of my stoneless plums has nothing but a jellylike substance to take the place of the seed. It is probable that plums actually seedless as well as stoneless will prove favorites with some fruit growers. 58 LUTHER BURBANK . cannot be propagated from the seed. But in this regard they do not differ from a number of i ee sa plants, the banana and the sugar cane, and many others. And for that matter it must be recalled that very few orchard fruits are reproduced from the seed. The favorite varieties of apples and pears are so blended that they do not breed true from the — seed. If you were to plant the seed apple, a Bartlett pear, or a Sugar prune, is only the remotest chance that you produce a seedling that would resemble the parent. : ! Yet apples and pears and prunes are prop- — agated year after year by means of buds and © grafts, The same method of propagation would of course suffice for seedless plums. | ) It would still be possible, however, to produce new varieties of seedless plums by using the — pollen of these varieties to fertilize the flowers — of other plums that were stoneless but not-— seedless. 3 The seedlings from such a cross would tend ' to vary in successive generations, as all hybrids © do. A certain number of the offspring of the © second and later generations would doubtless be — seedless, and it would thus be possible to develop — Hb THE STONELESS PLUM 59 new varieties of seedless fruit from a parent stock that is itself incapable of producing viable seed. The stoneless hybrids already produced repre- sent almost every color of the plum—white, pale yellow, orange, scarlet, crimson, violet, deep blue, almost black, striped, spotted, and variously mottled. They vary indefinitely in quality. Some of them are of abnormal size. They ripen from the middle of June until Thanksgiving. So the stoneless plum already constitutes a new race having numberless varieties, and the possibilities of further improvement are limitless. In producing seedless fruits we are simply hastening their evolu- tion for the benefit of man. THE ROYAL WALNUT ‘SPEEDING THE GROWTH OF A LEISURELY 'TREE F on visiting my grounds you were to notice two trees, one ten times as large as the other, growing side by side, you would perhaps be surprised to be told that the two are of the same age and grew from seed of the same parent. And it perhaps would not greatly clarify the matter in your mind to be told that these are varying individuals of a remarkable hybrid known as the Paradox Walnut. But probably your interest would be aroused in a tree that could show such diversity of progeny. The tree in question was developed more than thirty-five years ago. One of its parents was the native California black walnut tree; the other parent was the European tree usually called the English walnut, but with somewhat greater propriety spoken of as the Persian or soft-shell walnut. 61 A SIXTEEN-YEAR-OLD “ROYAL” WALNUT At sixteen years of age, the new “Royal” Walnut trees were sixty feet in height and as much in breathe we ee had a spread of branches only « * * a one-quarter that of the youthful “Royal.” This verity orighictd from ce a cross of Juglans Nigra and Sate: Californica, b's tm Denia i baat Abie cabbopdelt Veda nde dpe viata aR ld he Eire THE ROYAL WALNUT 63 The European tree had been introduced in California a number of years before the time of my experiments, where it thrives and produces abundant fruitage. I had heard of a supposed natural European hybrid walnut, and I deter- mined to make the experiment of fertilizing the fiowers of the California species with pollen from the Persian. The experiment itself presented no particular difficulties and the results were of a striking character. The nuts that grew from the hybridized flowers were to all appearance unchanged. This, of course, is quite what might have been _ expected, for the influence of foreign pollen on the ovum of a plant manifests itself in the innate qualities of the seed, and not in the exterior qualities of the fruit immediately produced. But when the hybrid nuts were planted the following season, a part of the seedlings that sprang from them showed at once the effects of the inter- mingling of racial strains. As compared with seedlings of either the California or the .Persian walnut, they mani- fested an enormously enhanced capacity for growth. Indeed, they sprang forward at such a rate as presently to totally dwarf their pure- breed relatives. 64 ‘The phenomenal growth of times ineAAnann: continued year after year. The tree so far out- stripped all competitors in the matter of growth that it might fairly be said to represent a new type of vegetation. At sixteen years of age these trees were sixty feet in height and as much in breadth of branches, the trunk being two feet in diameter at about four feet from the ground. Meantime © English walnuts on the opposite side of the © street averaged only eight or nine inches in diameter at thirty-two years of age, and had a spread of branches only about one-onethk that of the youthful Paradox. | tendency to droop. Tt makes a besutiful shu tree. The leaves are of extraordinary length, | sometimes measuring three feet, although usually — only about half that. Another curious charac- — teristic is that the foliage has a delicious apple- like fragrance, of which the foliage of the parent tree gives no suggestion. | These anomalies of growth and foliage show the mingling of racial strains. A further result — of this mingling is shown in the fact that the THE ROYAL WALNUT 65 hybrid tree produces very few nuts. It is obvi- ous that the two strains brought together are so variant that their progeny is made relatively sterile. The sterility is not absolute, however, for the few nuts produced germinate readily if planted. But another anomaly manifests itself in the characteristics of the seedlings thus produced; for these are the ones that show such extraordi- nary variation in size. In the same row, as already intimated, there will be bushlike walnuts from six to eighteen inches in height side by side with trees that have shot up to eighteen or twenty feet; all of the same age and grown from seeds gathered from a single tree. This rate of growth continues throughout life, and the fraternity of dwarfs and giants has been a puzzle to European and _ American laymen and botanists alike. These second generation hybrids vary as much also in regard to foliage and general character- . istics of form and development as in size. Some resemble the California walnut, others the Persian ancestor, and there are scores of vari- ations, the manner of growth of some of which— notably those that trail their limbs along the ground like a gourd or squash—bears scant resemblance to that of any walnut. From this Vol, 2—Bur, C WOOD OF THE “ROYAL” > WALNUT | It might naturally be supposed that — the “Royal” would produce a soft wood like that of most quick-growing trees. Such is not the case, however. The wood is harder than that of the black — walnut, and has the beautiful walnut _ color and grain shown in the photo- graph print opposite. te aes om es THE ROYAL WALNUT 67 extensive variation, it has been possible to select trees of even more rapid growth than the second generation hybrids, and the field seems to be open for the production, through selection in successive generations, of trees of still wider diversity of form and growth. Cur!ously enough the wood of the Paradox walnut is exceedingly hard, even harder and more close-grained than that of any other walnut. This is surprising in view of the rapid growth of the tree. Ordinarily trees that grow rapidly have soft wood, as mover? cabinetmaker knows. The Paradox further justifies its name by producing a wood that has great firmness of texture (superior in this respect to all other walnuts) and is well adapted to take on a cabinet finish. I had planted a row of these trees on one side of an eighty-foot street here in Santa Rosa, and, after making a few years’ growth, the street Was made impassable and the trees had to be removed. All in all the production of the Paradox hybrid, and the development of a race of hard- wood trees of exceedingly rapid growth, consti- tutes a genuine triumph in tree culture. A tree that grows to the proportions of a handsome shade tree and furnishes material for the cabinet- 68 LUTHER BURBANK mak in si o iter, ha ey evims economic importance, Tue Roya. Watnvt At about the time the Paradox was prodoned, I undertook another series of hybridizing experi-— ments with walnuts thet resolen eae: tam scarcely less anomalous. These experiments consisted of the conten of < the California walnut with the black walnut of © the eastern United States. The latter tree pro- duces perhaps the finest cabinet wood grown in America, but it has almost disappeared from our eastern forests owing to the rapacity and lack of foresight of the lumberman. The California and eastern walnuts are rather closely related, yet the divergence is sufficient to give the hybrid a character markedly different tom either parent. | In some respects this hybrid, which was christened the “Royal,” showed characteristics analogous to the Paradox. It had the same tendency to extraordinary rapid growth, and in subsequent generations it showed to a certain extent the same tendency to produce a varied company of dwarf and of giant progeny. There was also a considerable variation in foliage, although not the extraordinary diversity shown THE ROYAL WALNUT 69 by the second generation seedlings of the Paradox. In one important respect, however, the Royal hybrid differed fundamentally from the other. Instead of being relatively sterile, it exhibited the most extraordinary fecundity. The first generation hybrids probably produce more nuts than any other tree hitherto known. At sixteen years of age one of these trees produced a harvest of nuts that filled twenty apple boxes, each about two feet long by one foot in width and depth, and in one year I sold more than a thou- sand dollars’ worth of nuts from a single tree. The nuts themselves are closely similar in » appearance to those of the parent trees, but are individually larger. Unfortunately seed- lings grown from the nuts cannot be wholly depended upon to reproduce all the good quali- ties of their hybrid parents. Like most second generation hybrids, they tend to “throw back” to the divergent grandparent strains. To propagate the race extensively, therefore, it is advantageous to adopt the well-known method of grafting or selection of the strongest growing seedlings. It has been found that rootstocks of the Royal hybrid furnish very valuable stocks on which to graft the English walnut in California. On most ibe “PARADOX” WALNUT woop’ Be, eit TWO INCHES IN Diam ve RTER EACH YEAR The cross section of a “Paradow” Walnut trunk, pictured Pail a the annual rings of the tree, marking —— ite yearly growth. The photograph is we | made exact size, and it will be noted — < that some of the markings are an inch ‘. apart, thus showing that the tree in- Ra creased in diameter two full inches Ks within the year. On good lead mena crease of four inches in eee is usual. ’ THE ROYAL WALNUT 71 soils a tree grafted on this hybrid will produce several times as many nuts as a tree of corre- sponding age growing on its own roots. The trees are also much less subject to blight when they are thus grafted. It may be well to state here, as a matter of history, that the two first hybrid walnuts ever produced by the hand of man were first pro- duced on my own grounds and first named, described, and introduced by myself, GRAFTING THE WALNUT The importance of the new walnut and the _ fact that it may best be propagated by grafting makes it desirable to add a few details as to the method by which grafting is effected; for in the ease of the walnut the process is far more difficult than with ordinary fruit trees. Grafting the walnut is not, indeed, as difficult as grafting the pecan or the hickory, with both of which species the process was until recently found impossible of accomplishment. In this regard the walnut is rather to be likened to the fig, both being difficult to graft, yet not pre- senting insuperable difficulties for the skilled operator. Persons who first attempted to graft the wal- nut in California often failed four times out of 72 LUTHER BURBANK _ five; and budding was even less successful. But the importance of the subject led to a care- ful study of methods, and to-day grafters who thoroughly understand their work are so success- ful that they scarcely have more than two or three failures to hundred successful grafts. To attain such success, however, it is neces- sary to attend carefully to the various stages of the process. The grafting should not be at- tempted until quite late in the season; just after the buds begin to start is the most opportune moment. Hard wood should in all cases be selected for grafting; the pithy tips are utterly worthless for this purpose. Some grafters claim that only about two cions should be used from the base of the last year’s growth where the wood is very firm. Of course the principle of fitting the inside bark or cambium layer of stock and cion accu- rately together applies here as in the case of every other tree. Further details of the method _ will be given in a subsequent chapter, where the special methods of grafting and budding will be more fully examined. It suffices for the moment to emphasize the fact that these methods of propagation are as advantageous in the case of the walnuts, whether hybrid or of pure strains, as in the more familiar case of fruit trees. THE ROYAL WALNUT 73 Of course the stocks on which to graft must be grown from nuts, and I have already pointed out that the seedlings are likely to show diver- sity. But all that is necessary is to plant the seeds rather thickly, and then to save the seed- lings that show the best qualities. STARTING A WALNUT ORCHARD A practical method of producing a permanent and profitable orchard with a foundation to last for a century, is to plant some seeds of the Royal hybrid in groups of three or four at intervals of fifty feet each way. By the end of the first season the strong growers will have asserted themselves, and the others can be weeded out. There will almost surely be at least one good tree in the group. Failing that, there will be other groups in which there are extra seedlings of good quality that may be transplanted. The seedlings should be allowed to grow for four or five years, the ground about them being cultivated and may be used for crops of corn, potatoes, beans, or pumpkins, but preferably not sown with grain, lest the growth of the trees be checked. At the end of five or six years there should be a fine walnut orchard with trees having trunks three to six inches in diameter. 7 LUTHER BURBANK — Now the stock is ready for grafting. The stock branches selected for this purpose should not be over two or three inches in diameter. The cions grow rapidly and an orchard produced in this way surpasses all others. Its trees have a — natural black walnut vigorous system of roots, with undisturbed tap root. A year’s growth has been saved by not transplanting, and a start equivalent to the growth of several years has been gained by using the faster-growing hybrid. = So the English walnut grafted on this stock becomes a producing tree at a very early age, and — an orchard of English walnuts thus grafted is worth perhaps at least twice as Se own roots. | The tree thus grafted has not only the adv tages mentioned, but it is more om therefore more productive than the tree; and Ose otcenil of Sibits Ghana root system, which thus insures a good supply of nourishment and the capacity to produce large : crops even in dry seasons. We have seen that the hybrid: walnuts 8 dds the Paradox and the Royal types have the peeul- iarity of producing trees of quick growth and gigantic stature in the first filial generation, and a mixture of dwarfs and giants in the ‘second generation. THE ROYAL WALNUT 75 Tue STRANGE TRAITs oF Hysrips The tendency to surpass their parents in size is a characteristic that is very commonly mani- fested when plants of different species are hybridized. It is a familiar and now well-recog- nized fact that the crossing of diverse strains of living creatures, plant or animal, tends to result in what for lack of a better term is usually described as increased vitality. It would appear as if the conflict of new tendencies so stimulates the cellular activities as to give them an unwonted capacity for reproduction. In this case we are not concerned, as we were in some of the other hybridizing experiments already examined, with the prepotency or domi- enance of the qualities of one parent. Instead of this there is a distinct blending of characteristics so that the new product is in many respects inter- mediate between its parents in matters of foliage and fruit. But in growing capacity it far sur- passes them both. Thus we have produced, as the offspring of the slow-growing English walnut and the not very rapidly growing California species, a tree that grows so rapidly as presently to tower far above either of its parents. VARIATION IN HYBRID WALNUT LEAVES | With thie work, a with alt other — cceathis of those soidibees which have a the largest and best leaves, and the best leaf formation. Many seedlings, prom- ising in other respects, have faulty — leaves, and promptly go to ewell the ~ bonfires of rejected plants. | THE ROYAL WALNUT 77 As to form of leaf and fruit the hybrid may resemble one parent in one direction and the other parent in another. The leaf of the Paradox walnut, for instance, more closely resembles the leaf of the English parent. The outside appear- ance of the Paradox nut is also similar to that of the English walnut. But on breaking the shell we find that it is thick and strong like the shell of the American species, and the kernel is rela- tively small, quite different in form as well as in flavor from that of the English walnut. It cannot be said that anyone has a very clear notion as to precisely what the changes are that give to a hybrid race this enhanced vitality. But this mystery is after all only part of the great all-pervading mystery of heredity, which in turn is merged with the mysteries of life processes in general. Wuy Some Are Dwarrs What I shall consider a little more at length here, however, is the conduct of the seedlings . of the second generation grown from either the Royal or the Paradox hybrids. How does heredity explain the observed fact that some of these are dwarfs that can by no process of urging be made to attain anything like the average stature of walnuts in general, whereas others, sprung from nuts grown on the 78 LUTHER BURBANK — hybrid parent, not to mention their moderate- sized grandparents? The fact of this diversity is unquestionable. It affords a surprise to all who | inspect the trees of this — Gnerited fraternity. But how explain it? ih chive 46 the exzpliciatitns So gual a learn that a California walnut, which, it will be recalled, was a parent form in each of the hybrid strains, is a tree showing great variability in the matter of size when growing in a state of nature. In the northern and central parts of California it is usually a large spreading tree, often with gracefully drooping limbs. But farther to the south it becomes a mere shrub, and on the moun- wok Theat deuce te a bush. The nut diminishes in size co until, in Texas and Mexico, it is scarcely larger than a pea. When growing still farther to the south, in New Mexico and Texas, the black walnut is sometimes classified as a different species. It appears to me, however, that these dwarfed southern forms are only varieties that have ac- quired different characteristics through the in- fluence of what for them has proved an unfavor- able environment. In any event there is no THE ROYAL WALNUT 79 reason to doubt that the dwarf form and the rela- tively large one are descended from the same original stock, though doubtless divergence has gone on through numberless generations. Meantime the English or Persian walnut, the other parent of the Paradox, is also a variable tree. In its native home it is very small, and even the cultivated variety cannot be depended upon to reproduce a given racial strain when grown from the seed. It is obvious, then, that the tendency to dwarf- ness, which appears in such conspicuous fashion in some of our second generation hybrids, may be accounted for as reversion to dwarfed ances- tral strains in both parents in the case of the Paradox and of one parent in the case of the Royal. The tendency to grow relatively large pre- vailed in the strains of walnuts that were used in _ my hybridizing experiments, and the prepotency or dominance of this tendency is clearly shown in the hybrids of the first filial generation. But the latent tendency to dwarfness, which in the Men- delian phraseology would be termed a recessive trait, is able to reassert itself in a certain number of the offspring of the second filial generation, causing these to “throw back” to their dwarfed ancestors in the fullest measure. THE ROYAL WALNUT 81 The capacity for large growth has been abso- lutely left out of their individual make-up. In the Mendelian phrase they are pure reces- sives; or, using the more technical terminology, they are “homozygous” as to the heredity fac- tors or determiners of the unit character of dwarfness. The reader may or may not feel that the new terminology adds to our comprehension of the phenomena. But in either case the fact of the appearance of the dwarf specimens of the second generation among the hybrids is at least in a sense explained by our knowledge that there were dwarfs in their ancestry. How Account FOR THE GIANTS - But while we are thus supplied with a more or less satisfactory explanation of the appearance of the dwarf hybrids, the colossal companions of the same generation are as yet unaccounted for. It is a familiar fact, as just pointed out, that hybrids of different species do tend to take on new capacities for growth. But what hereditary warrant have the upstarts for thus outdoing their parents? So far as we are aware, there is no record of a pure-bred walnut of any of the three species involved that ever showed such capacity for rapid growth or such propensity to 82 LUTHER BURBANK anne Sree Sane See ee tions as the hybrids manifest. Theseg no reedtded ‘or-chedesead Maciel ta whom we can appeal in explanation of the de- velopment of these new races of giants. As yet we are not denied at least a cal explanation that may perhaps account for the observed colossal growth of these new races of trees. The explanation demands that we go back in imagination through very long periods of time, and consider the ancestors of our wal- nuts not merely for hundreds of generations but for thousands or perhaps for millions of generations. Hi fa necessary, isi slice’; to tran hannaneanene ancestral history of the walnut to those remote epochs when the primordial strain from which the present trees have developed grew in tropical regions, and, in common with tropical vegetation in general, doubtless acquired the habit of luxu- riant development. It is permissible even that we should place in evidence the exuberant vegetation of that remote geological era known as the Cretaceous Age. In that time, as the records in the rocks abundantly prove, the conditions of climate now restricted to the tropics prevailed even in the temperate zones, and the vegetable life was char- THE ROYAL WALNUT 83 acterized by the abundant production of colossal forms. In successive ages the climate changed, and it became necessary for the plants that were unable to maintain existence under the changed con- ditions to adapt themselves in size and in struc- ture to a less bountiful supply of foodstuffs drawn from both soil and air; for the soil of the temperate zone is relatively arid, and the air probably became progressively less rich in car- bon, owing to the permanent storage of vast quantities of this substance in what ultimately became the coal beds. So it came about that all the descendants of the colossal plants of the Cretaceous Era formed races that were dwarfs by comparison. Here and there a straggling species, like the California redwoods, preserved a reminiscence of its imposing heritage. But in general the trees that make up our forests in the temperate zone are but insignificant representatives of a lost race of giants. These, then, are the remote ancestors that may be invoked in explanation of the rapid growth and relatively gigantic stature of our hybrid walnuts. In this view the exceptional growth of these hybrids betokens reversion to remote ancestral strains that for countless generations have not A GRAFTED WALNUT TREE The selected varicties of walnuts do not breed true from the seeds, so it is — necessary to graft them in making commercial orchards, just as in the — case of the orchard fruits. This is a typical specimen grafted on the — “Royal” black walnut. THE ROYAL WALNUT ~— 85 been able to make their traits manifest, but which have always transmitted these potentialities as submerged and subordinated tendencies. The admixture of the divergent racial strains—one from Europe, the other from California, or in the case of the Royal, from origins senarated by the breadth of a continent—sufficed to bring together factors of growth that for all these generations had been separated, and the atavistic phenom- enon of a giant walnut came into being. Thus interpreted, the case of the big walnut is not dissimilar to the case of our white black- berries or to that of the fragrant calla. In each of these instances, as in that of num- berless others that we shall have occasion to ex- amine, a mixture of racial strains brings about a reversion to the structure or quality of a remote ancestor. In the case of the walnuts we have had occasion to go back a few thousand generations farther than in the other cases, but there is ample warrant for believing that nature sets no limit on the length of time throughout which a submerged character may be transmitted, with full possi- bilities of ultimate restoration. We shall have occasion to examine further evi- dence of the truth of this proposition, drawn from a quite different field, in a later chapter. Here, for the moment, we may be ‘cldeeened merely to place our colossal walnuts in evidence. Towering above their dwarf blood sisters, they present a vivid object lesson in heredity that appeals directly to the senses and strangely stini- ulates the imagination. 8 hare HAT gee ae oe 2 RSP eS: Nature sets no limit on ag lh ir length of time throughout which — a submerged character may be transmitted. THE WINTER RHUBARB MAKING A Crop For A HicuH- -Pricep MARKET ORE than one enthusiast has declared that the most important garden vege- table that has been introduced to the world in the past half century is the giant crimson winter rhubarb, This no doubt is an overestimate, if for no other reason than that it overlooks the Burbank potato or the thornless blackberries or the new series of giant shipping plums. Still, there is no question that my winter rhubarb has proved to be of great economic importance. Although intro- duced quite recently, it has already made its way to all quarters of the globe, and has proved of unusual value in regions where no other rhubarb had hitherto been, or could be grown. At the Cape of Good Hope, for example, efforts to grow rhubarb had been made for two hundred years at least, and always without suc-, cess; but the new variety proves an especially sat- 87 88 LUTHER BURBANK > interest a conservative Greet Beliay Sia older varieties thrive and have been & 3 grown, specimens having been obtained direct | from my plantation by Robert mes ber of the Royal Horticultural Society, ? others. The royal gardens of England are now ; supplied with it. i Me Meantime the Emperor of Japan aiid tel ‘ing of Italy obtained it directly from my gardens and the plant has been taken back to its original home in New Zealand, from whence came the material for its production, and in its improved or, one might better say, metamorphosed condi- tion, it now finds favor there, whereas its ances- — tral form was justly regarded as a plant of no importance. Bea eh 3 Tue QvaALities or THE NEw Rustad It must not be supposed that this wanig i tended approval of the rhubarb is dependent on _ any mere caprice. It is based on qualities of the most enduring and substantial character, other- wise it would not have been possible to plant Ssblinds of acres of this crop in California and to find a ready market for the entire productin the eastern United States. In point of fact, so _ THE WINTER RHUBARB 89 eager has been the market that the rhubarb has been quite often called by its growers the “king mortgage lifter.’ Many substantial fortunes have been made by growing it here in California and shipping it to the eastern States during the holiday season when fruits and green vegetables are relatively scarce. It retains, as to general appearance, the aspect of the usual stalk of the familiar rhubarb or pieplant of the eastern vegetable garden. But the stalks are of a characteristic rich crimson color, and as brought to the table the sauce made from them is not only delicious in flavor, sug- gesting the strawberry and raspberry, but it is quite devoid of the stringiness or fiberlike texture and the disagreeable “ground taste” of the ordinary pieplant. Many people who have hitherto regarded pie- plant as a plebeian dish to be avoided are en- thusiastic in the praise of the new product. The crimson winter rhubarb produces not only far larger stalks than the old New Zealand prototype, but at least ten times as many of them to each plant. The stalks begin to appear in great abundance early in September and con- tinue to produce a product of unvarying quality for eight to twelve months together—in Cali- fornia throughout the entire year—instead of + taal aa 90 LUTHER BURBANK for a few weeks in the spring. So the popular of the winter rhubarb from the standpoint o grower as well as of the dealer and con is not hard to understand. $a It may be added,'as further evidene unusual qualities of the new plant, that i in almost any soil, although giving ¢ sponse to good conditions of cultivatior older varieties; that it propagates rea mains altogether true to the perfected typ that it is unusually productive and requi unusual attention, so that any amateur ma it in his garden even more readily Ws It must be understood, hocnaven Ain he plant cannot thrive in latitudes where it is k nder snow; the shoud pecans eae to be essential to its very existence. — ee In the colder parts of California it does in ndeed — cease to grow actively in the heart of winter, but even then it submits to adverse conditions reluc- tantly, if the phrase may be permitted; that is, \ it stops putting forth new leaves bas when the conditions are exceedingly ble a immediately resumes new growth when — slightest change for the better in the wonthet occurs. cm THE WINTER RHUBARB 91 THE ORIGIN OF THE WINTER RHUBARB The importance of the new plant, and its wide departure from the traditions of the rhubarb family, might lead one to suppose that the pro- duction of the new variety had been a task of great difficulty. Perhaps from the standpoint of the average plant breeder it could hardly be said that its creation was altogether easy; yet compared with some of my other plant develop- ments the production of this one was at least relatively simple. . The original stock from which the new variety was developed came to me from the antipodes. It was sent vy the firm of D. Hay & Son from Auckland, New Zealand. The first two or three shipments were lost, as the plants died on the way, but at last I obtained half a dozen very diminutive roots that showed some signs of life. These, as anticipated, produced stalks during the winter instead of following the conventional rhubarb custom of putting forth stalks for only a few weeks in the spring. The stalks of this original winter rhubarb, however, were very small—about the size of an ordinary lead pencil—and certainly not worth cultivating for immediate use, as they would A TYPICAL PLANT _ This picture shows a single plant of the Giant Winter Rhubarb that grows _ to the height of almost four feet. — The handsome crimson stalk contrasts finely with the green foliage. The quality is far superior to any othe, — rhubarb, and the production of the stalks is perpetual throughout the whole year. The flavor is much more like that of strawberries than of the old~ — style rhubarb. THE WINTER RHUBARB 93 have proved quite unmarketable. The plant was admitted to have no great value in New Zealand. Indeed, in point of value the imported plant bore no comparison with ordinary pieplant of our gardens. It was solely and exclusively the quality of winter-bearing that made the plant appeal to me and suggested the possibility of developing from it a valuable addition to our list of garden vegetables. My original stock of half a dozen plants soon increased to a hundred or more. These plants produced seéd abundantly in successive years, and all this seed was carefully planted and the seedlings that grew from it, to the num- ber of hundreds of thousands, were closely examined and tested as to various desirable qualities. From among the thousands I was able to select here and there a plant that showed exceptional qualities of growth, standing well up above its companions of the same age. Of course selection was made of the plants showing this exceptional virility, and in the course of a few years I had thus developed, by persistent selection, a race of plants that grew with extreme rapidity, and to a size, by comparison, quite dwarfing that of the original parent stock. tas! ‘otture andl: diea oh Aaa ) referred to, but they retained and advanced upon the tendency of their ancestors to grow con- — stantly throughout the year. This anomalous tendency, rather than the improvement in the — other qualities of the plant, is obviously the one that requires explanation. Remarkable im- — provement in size and in other desired qualities, — through selection, is a more or less — pence method of plant development. a But the production. Gf «secs of plagieaslanal : departs radically from the most pronounced and characteristic trait of the rhubarb family, namely brief period of ‘bearing; 2s ani | quires explanation. rae: A clue to the explanation is found whenwe. | recall that the plants were sent me from a region lying on the other side of the equator. The plants were exceptional even there in that they had shown a tendency to bear—that is to say to produce small juicy leafstalks—during the cold — season. Through some unexplained freak of | heredity or unheralded selective breeding they had developed a character that had enabled them to put forth their leaves much earlier than is customary with all other races of rhubarb, THE WINTER RHUBARB 95 The difference was only a matter of weeks, and was of no greater significance, perhaps, than the observed difference in time of bearing be- tween different varieties of other vegetables and fruits. Everyone knows that there are early and late-bearing varieties of most commonly culti- vated vegetables and fruits— summer apples and winter apples furnish a familiar illustration. Perhaps some one had discovered a root of rhubarb that chanced to have peculiar qualities of hardiness, and had propagated it until he had a variety that begari bearing while the relatively mild New Zealand winter was still in progress. But this is only the beginning of the story. The sequel appears when we reflect that the season that constitutes winter in New Zealand is coincident with the summer time of the Northern Hemisphere. So when we say that the crimson rhubarb was productive during the winter in its original home, this is equivalent to saying that it had the habit of bearing during our summer time. Trans- planted to California, the New Zealand product continued to put forth its stalks, quite in accord- ance with its hereditary traditions, during what, according to its ancestral calendar, was the win- ter season, although the climatic conditions that now surrounded it were those of summer. 96 LUTHER BURBANK its Ghat Tue INFLUENCE OF ENVIRONMENT pe But meantime this plant, like every ae | living organism, was of course subject to the directly stimulative influence of its environment. Its hereditary traditions had developed what we may speak of as an instinctive tendency to grow at a given time of year regardless of climatic conditions; but they had also given it an equally — powerful tendency to respond to the stimulus of — cold weather, and to become productive not — merely in thie Sebvon of -witter: SE climatic conditions of winter. In other words, the combined infininibed! ret heredity and of immediate environment were here as always influential in abarrnay eie cig! ditions of plant growth. But, whereas in New Zealand the envivorieuad of winter—characterized by cold temperature— coincided with the calendar months of June, July, and August, in the new environment of California the conditions of winter were shifted to the calendar months of December, January, and February. So the two instincts, one calling for productivity in June, July, and August, and the other for productivity during cold weather, were now no longer coincident, but made them- selves manifest at widely separated seasons, thus THE WINTER RHUBARB 97 perhaps aiding in the production of a perpetual rhubarb. So the net result was that, merely through the retention of old instinctive habits under the trans- formed conditions imposed by migration to the Northern Hemisphere, the winter-bearing rhu- barb of New Zealand was transformed, by most careful and persistent selection, into a summer and winter-bearing plant in California. And inasmuch as there are no sharp lines of demarca- tion as to just when the pieplant begins and ends bearing, the two seasons tended to merge, with the practical result that some of these plants became all-the-year bearers. THE Power oF Hapsit Possibly the use of the words habit and in- stinct as applied to a plant requires a few words of elucidation. We ordinarily take the habits of a given plant so much as a matter of course that we are prone, perhaps, to overlook their close correspondence with the habits of birds and animals and other animate creatures. Yet a moment’s considera- tion will make it clear that we may with full propriety speak of the fixed or regular “habits” of plants, and that there is no logical reason why we should not speak of them as being Vol. 2—Bur. D 98 LUTHER BURBANK — : determined by “instinct,” which after all sug ‘Arad the force of the warious Bamana aan in the case of a plant, as in the case of birds and animals, is overwhelmingly powerful cmap : beyond the possibility of change in any generation. He age To cite a single illustration from thecal hand, every gardener knows that he cannot by any process of cultivation make the ordinary rhubarb plant change its fixed habit of spring production. No amount of coaxing and no man- ner of soil cultivation or fertilization can take from the rhubarb the impelling force of the hereditary tendency to put forth its stalks in the spring time rather. thas J saeaaaaaes or winter. And a similar fixity of habit chareehenionss i greater or less measure, most other familiar cultivated plants. Artificial selection has ex- tended the season in certain cases, and early or late-bearing varieties have been developed as already noted; but for each variety the habit of producing at a given time of year is one of the most fixed and—as regards any given ated tion—unalterable of tendencigs. Ee eet ae ope ae a a ape Br ty a neg ee Bai ace THE WINTER RHUBARB 99 ILLUSTRATIONS FROM BIRDLAND Perhaps the all-importance of this inherent tendency to gauge habits in accordance with the calendar will be more clearly apprehended if we cite another illustration from the organic world. Take the migrations of birds as a familiar instance. If you watch the birds at all, you have doubtless noted that the migrants that come to temperate regions from the tropics arrive each spring in your neighborhood at a date that you may fix in advance with almost entire certainty. The hardier birds, to be sure, such as the robin, the bluebird, and the meadow lark, retire before the blasts of winter somewhat unwillingly and they begin their northward migration at a period that may vary by a good many days or even weeks according to the forwardness or backward- ness of the season. But the coterie of tender birds—orioles, vireos, wood robins, tanagers, fly- catchers—which spend the winter in the region of the Equator, must begin their northward migration without regard to the climatic condi- tions, inasmuch as their winter home is a region of perpetual summer. They start northward merely in obedience to an instinctive time sense that has been implanted through long generations of heredity, and they 100 LUTHER BURBANK move across the zones with such scheduled regu- larity as to reach any given latitude almost eas fixed day year after year. In Massachusetts or New York or in Oblo ar in Iowa, for example, you will find the last flight of migratory birds, comprising the various species of wood warblers and vireos, the orioles, __ and the scarlet tanager, appearing between the tenth and fifteenth of May each year, without regard to the advancement of the season. = And a few months later you will note, if you are observant, that these and the other migrants disappear in the fall, having taken up their re- turn voyage at about the same calendar period year after year, although in one season the Sep- Teather days may bp Se hot ss Ae another season chill as November. Countless generations of heredity hheve fied in the mechanism of the bird’s mind the instinct that impels it to migrate at a fixed season; and no transient or variable conditions of the imme- diate environment can alter that instinct, even though, in a given case, its alteration might be vastly to the advantage of the individual. Even Unto DeatH As proving the latter point, and as further illustrating the force of the instinctive time sense THE WINTER RHUBARB 101 under consideration, let me recall the case of the martins to which reference was made in an earlier chapter—the case in which these birds starved to death because in a particular season drought pre- vented the hatching out of their insect food. Everyone knows that the mariin is a bird of very swift and powerful flight. Its estimated speed is more than a mile a minute, and it habit- ually remains hour after hour on the wing. It was easily within the capacity of the martins that starved to death in New England to have shifted their location at the rate of more than a thousand miles a day. And assuredly within half that distance, prob- ably within two or three hundred miles at the most, they would have found an abundant supply of food. Now the season at which the martins actually starved was August; only a few weeks, therefore, before the time of their regular autumnal migra- tion. Had the birds lived another month they would instinctively have begun a long journey to the south, and a single night’s flight would have brought them to regions where no doubt their food needs would have been abundantly supplied. From a human standpoint, it would seem only natural that the birds, deprived of food, should have begun their seasonal migration 102 LUTHER BURBANK a few weeks before the usual time; whereby thi 4 lives would have been saved. Whoever understands the force of hervdliduss instinct will realize that such a departure as this was for the birds impossible. The instinct of migration comes to the martins in September, not in August, or at least not in early August. ‘The habit of migration isnomore determined by any conscious judgment of the bird than is the habit of spring growth deter- mined by a conscious judgment of the rhubarb. The force of untold generations of ancestors impelled the martins to remain where they were, even though starvation was the penalty, __ Wings they had, with which they might have sought and found a new environment where food was plentiful; but they were powerless to use the wings at this particular season, because the __ particular week had not arrived at which the hereditary clockwork of their organisms would strike the hour for migration. Taken by the ass ot large, is ia ether dom Se eee should not migrate until September; this fact had been established through the test of thou- sands of generations, and the result was regis- tered indelibly in the organism of every bird. Were it possible to destroy the racial tradition in the interests of any single generation, the life THE WINTER RHUBARB = 103 habits of the species would become so variable and desultory that racial continuity would be endangered. So the individuals of a generation throughout a large region were sacrificed to a racial instinct which in the main was beneficial to the species. It will be clear, I trust, how this illustration bears directly on the case of our winter rhubarb. RESTORING SUBMERGED INSTINCTS. It could make no difference to the roots-of this plant that they had been unwittingly trans- planted from a land where winter comes in July to a land where that month betokens summer. The instinct of bearing at that particular season had all the force of the instinct that impels the bird to migrate at a given time; and this instinct could by no chance be repressed in a given gener- ation, any more than the martins could make over their migratory instinct to fit a transitory condition. But all this leaves quite unexplained the other fact, which bore so important a part in our story, that the New Zealand rhubarb when transplanted to California assumed a new habit of bearing during the.cold season of the Northern Hemis- phere which corresponded to the summer of its original habitat and therefore to a calendar 106 LUTHER BURBANK accustomed to assume a condition of do Flow fo our theme of the poner aca 4 habit to be made to coincide with this seemingly illogical departure? Our answer is found, as it has been found in the explanation of other anomalies of plant development, in an appeal from the immediate ancestry of the rhubarb to the countless galaxies: 4 of its vastly remote ancestry. In point of fact the rhubarb is, in all probe ability, a tropical plant that has but recently migrated to temperate zones—using the word recently in the rather wide sense necessary when we are dealing with questions of racial develop- — ment under natural conditions. In other words, it is perhaps only a matter of a few hundred q generations since all the ancestors of the existing _ rhubarb tribes were growing in a tropical tem- perature, and hence, like the tropical mca 4 general, were all-the-year bearers. In more recent generations, this habit of per- petual bearing has been modified, in case of the — 4 rhubarb as in the case of nearly all plants of temperate zones, to meet the altered condi- tions of a climate in which seasons change. To adapt themselves to this change of climate, plants were obliged to go into retirement in the THE WINTER RHUBARB § 105 winter season, and natural selection preserved only the races that showed this adaptability of habit. Thus the common race of spring-bearing rhubarb, as we know it, was developed. But the latent capacity to bear at all seasons— to live a fully rounded life throughout the year which may be considered the normal and in- herent propensity of all living things, and which is. observed to be the habit of tropical plants in general, was never altogether lost. Submerged generation after generation and century after century, the hereditary factors that make. for perpetual growth were still preserved, capable, under changed conditions, of being resuscitated and of making their influence manifest. The changed conditions came, in case of the rhubarb, when the plant found itself in the new environment of California. New soil, new atmosphere, new climate—all these are stimulative. Then successive genera- tions of the plants were bred from seeds, and we have already seen that the mixture of strains thus effected tends to have a disturbing influence on the life forces permitting new combinations of characters and resulting in the development of new forms. We saw this in the case of the Shasta daisy and very notably in the case of the hybrid wal- eee ee Tt me READY FOR SHIPMENT The handsome appearance of the Crimson Winter Rhubarb adds greatly to the attractiveness of this “vegetable _ and fruit” in the market. We have a ‘ given particular attention to the devel- _ oS opment of plants that will grow stalke of a uniform size, this being an obvious additional advantage in marketing the product. The color of the Winter Rhubarb gives it added attractiveness — when it finally comes to the table. Fa ig i a a a A ET SRO NT Rerk re ea oe site st ie ee techs loan te ae Len se Pa Sa Te, Mae ee Ree eee eh Eee Gey Tat ese ie ea i 2 A AN a MS ell Sm a i Ie RE EE THE WINTER RHUBARB 107 nuts. We shall note the same thing again and again in connection with a multitude of other plants. In the case of the rhubarb, the response was almost immediate. Artificial selection en- abled the plants that manifested the atavistic tendency in largest measure to propagate their kind. And, thus, in the course of a few generations —though not without making selection among hundreds of thousands of individuals —I was enabled to assist the plant to bring to the surface the long submerged tendencies that impelled it to grow fast, to grow large, and to grow per- petually. No New Princierte INVOLVED And thus the crimson winter rhubarb as it finally came to perfection in my gardens is accounted for. In developing it, no new princi- ple was invoked, no new method even. I merely took advantage of opportunities afforded by the translation of the plant from one hemisphere to another, and aided the plant in putting forth potentialities that had long been repressed but which still stubbornly persisted as latent factors or submerged tendencies in the racial germ plasm. 108 Perhaps the matter seems rather complex as thus explained; and indeed all matters pertain- : ing to living organisms are complex in the last analysis. But the methods of operation were in practice simple. Granted certain conditions and certain hered- itary tendencies; granted, in other words, the materials with which to work, it required only clear-eyed selection and patient waiting—the encouragement of some tendencies in the right direction and the suppression of other tendencies in the wrong direction—to produce the desired result. 3 PROPAGATING THE WiInTEeER RHUBARB To make the story complete, however, it should be recorded that although the winter rhubarb was developed by mere selective breed- ing of a pure strain, yet the experiment was not carried forward without numerous tests of is hybridizing method. From the outset the New Zealand plant was crossed with the native rhubarb, hoping thus to stimulate variability. And, almost needless to say, variability was stimulated. The hybrid plants took on sundry forms and diverse habits. But it chanced that no one of these forms was an improvement on those THE WINTER RHUBARB 109 that were secured by selection from the pure New Zealand stock. Nor did this New Zealand stock, even when developed into my new all-the-year bearer, prove capable of sure propagation from the seed. It can readily be propagated by dividing the roots or by cutting out little sections of the root containing a bud, so there is small neces- sity of development from the seed. But in this case, as with so many other cultivated plants, it is essential to use this method of propagation if we wish to have an absolutely fixed variety. An obvious explanation would be that the original New Zealand rhubarb was of mixed racial strains. This, indeed, would account for its tendency to vary, and to contribute to its suc- cessful development in California. The inter- breeding which produced the winter-bearing strain may have been done quite by accident in New Zealand, the plants that came to me em- bodying the germs of possibilities of develop- ment without further hybridizing. PERPETUAL BEARING Now FYIxep It should be added, however, that even when grown from seed, the new winter rhubarb always manifests the tendency to perpetual bearing. 10 LUTHER BURBANK This one trait is fixed, though some of the other qualities of the plant are still variable. — oe Using the new terniinslogy anemia ie the tendency to winter-bearing is a unit character _ that is latent or recessive, and that the winter rhubarb has no factors of the opposite trait of limited bearing and therefore cannot revert so long as it is inbred. When crossed with the — ‘ spring-bearing race, however, the offspring some- __ times revert to the old habit, as nalght be a expected. As already noted, nothing so far has rae : < gained by such crossing. Nor is there any neces- __ sity for the growth even of pure-bred seedlings. — Propagation by root division answers every pur- pose and, thus multiplied, the new crimson winter rhubarb, in its perfected varieties, con- ‘stitutes 6 fixed race and is © Dee sition to the list of garden vegetables. It required only clear-eyed selec- tion and patient watching—the en- couragement of tendencies in the right direction and the suppres- sion of tendencies in the wrong direction—to produce the result. Es Pre nN 1 ES aE rae RT aT er ON ae er wee ee ee Oe THE BURBANK CHERRY THE EXPLANATION OF A DOUBLE IMPROVEMENT " OW many assistants have you in your H orchard?” a visitor asked me. And when I replied, “About a hun- dred thousand this morning, I fancy,” my visi- tor looked quickly this way and that across my eighteen-acre Sebastopol farm, and then seemed politely incredulous. “T don’t see quite so many,” he remarked. “In fact, I can see but eight.” “No,” I said, “you don’t see them; but you can hear them if you listen. They are mostly up there among the cherry blossoms. Notice how their wings hum as they go from flower to flower.” “You mean the bees?” “Just so; the bees—they are my most impor- tant helpers at this season. I should get no cherry crop without them, and for that matter no plum crop, no apple crop, and very few 111 112 LUTHER BURBANK — flower seeds. In fact, most of us who grow fruit would soon go out of business, or reduce our farms from acres to square feet, if it were not for the bee helpers busing abot Se to blossom.” “But do you depend entirely upon the bees . to pollenize your cherries?” my ee continued. “Not altogether. I am obliged to do some pollenizing, particularly at the beginning of an experiment, to make sure of the exact cross that I desire. But after the experiment is under way, the work is for the most part left to the bees. They operate, as you see, on a large scale, mak- ing a thousand pollenizing experiments where I could make one. And in the end: ty aaaaers their work are highly satisfactory.” How Po.ientzation Is Errecrep To illustrate the necessity for the aid of the insect helpers, it is well to show the method by which cross-pollenizing is effected when done 4 human hands. A blossom is selected that is almost matirs but has not opened, and is cut all around with a very thin, sharp knife, taking the petals about two-thirds the way down, thus amputating all the stamens, but leaving the pistil. Pe a Th hae ate Ae Ee, Pee, en eae Pe Sy ee ee THE BURBANK CHERRY 113 Pollen which has previously been collected upon a watch crystal from some open flowers is applied by lightly touching the finger to it, then to the stigma, taking care to cover the top of the stigma completely with the pollen. This is a simple enough procedure, but it must be done carefully, as the number of tests that one experimenter can manage-is limited. Moreover, it is necessary, of course, in a case that calls for hand pollenizing, to mark the blos- som with a tag of some sort, else there would be no record of the experiment, and no way of tell- ing whether it finally proved successful. Again, it is usually desirable to remove other blossoms from the cluster in which the artificially pollen- ized one grows, to give a better opportunity for development of this individual. If, finally, we are to make absolutely certain that no other pollen comes in contact with the stigma, thus guarding against the possibility of fertilization of the flower by other pollen than that intended, it may be desirable to tie a paper bag over the flower. The latter procedure is not usually necessary, particularly if care has been taken to cover the stigma with pollen, as once this is dene there is almost no danger that any foreign pollen will find lodgment. Moreover, the flower from which the 14 LUTHER BURBANK petals have been cut, an just:densiliial aan | hp festilined ab ll if ou pase tion should for some reason fail. Time THe Limirine Factor Aigo But even when restricted to the cosentiale; the | 1 process takes time; and although some thousands of hand pollinations are done annually in my gardens and orchard, yet, as intimated, we try to leave the bulk of this work to the bees. Of course, these otherwise admirable helpers make _ no distinction between different varieties of blos- soms, passing freely from one tree to another, — regardless of the variety; but they usually con- fine their attentions on any given day to trees of _ a single species; that is to say, they do not ordinarily pass from cherry blossoms to the blossoms of the plum or almond, even if all are in season. They seem to prefer not to mix their — sweets. So they do not distribute pollen to the wrong flowers as often as might be supposed. — Where pollenizing experiments are to be madd on a larger scale, I sometimes place a branch of — a cherry tree in full bloom among the branches of the tree of another variety, with which I wish to effect hybridization. The bees then transfer the pollen from the borrowed limb to the flowers THE BURBANK CHERRY 115 on the surrounding branches, and a_ thor- oughly satisfactory cross pollination is often thus brought about, as anyone of any experience knows. If a visitor who observes my cherry trees in the blossoming time chances to visit my orchards a little later, at the time of fruiting, he will prob- ably be disposed to admit that my various meth- ods of experiment have produced very satisfac- tory results. For the cherries that grow on my trees are the largest and most luscious, as well as the most abundant, that have ever been produced, and the visitor will perhaps be surprised to find many hundreds of cherries quite different in appearance sometimes growing on_ the same tree. This, however, is only the result of grafting. Seedlings grown from seed produced on a single tree may vary widely, but the immediate fruit of any individual tree is fairly uniform, un- less the tree has been grafted. But trees on my farm always are grafted, so the phenomenon of diverse varieties of fruit on the same tree is a familiar one. AN UNSTABLE RACE The cherry is at best a variable fruit. Like most orchard fruits, it can never be grown de- THE BURBANK CHERRY 117 pendably from seed. But, of course, it is neces- sary in producing new varieties to work from seedlings, and from the standpoint of the experi- menter who wishes to produce new varieties, it is fortunate that the tendency to vary exists. For, as our other experiments have taught, in the case of plants already described, it is only when a tendency to vary from a fixed racial type has been brought about by hybridization, or other- wise, that the material is furnished upon which the experimenter can build. In the ease of the cherry, all the familiar varieties are the result of hybridizing uncon- sciously in the past. By working with the seed of any single exist- ing variety, one secures plants of numerous types that suggest different possibilities of de- velopment. Tue IpeEAL CHERRY In the course of these experiments, however, I have had occasion to bring together, through artificial pollenization, various standard varieties of the cherry, and, although it has not been found to be necessary to send to foreign countries, yet the stock with which I have worked represents races which have been developed in regions as widely separated as Russia, the eastern United States, California, and Japan. . = 2 qualities of different of = lings of widely diverse types. ni eee The foundation stock swith while chiefly was the variety known as Early Purple Guigne, crossed with the Black Tartarian; but in subsequent crosses the qualities of Russian, — French, and American cherries and of numerous othe ‘were intzocuoced, in ats “tena ara the ideal cherry. | A familiar but notable characteristic of tha a cherry, in which it differs markedly from most — other fruits, is its habit of ripening at the very — beginning of summer, while many of the small — fruits are not yet in blossom. This character- istic gives the cherry peculiar commercial value, as it comes on the market at a time when there is a a scarcity of fruits. a It occurred to me many years ago that fe : would be a still greater advantage if a good — cherry could be produced that ripened much 4 earlier than any variety then known. Sh es So early ripening was one of the first ideals i at which I aimed. With that object in view it — was natural to select for these early hybridizing _ so eehiacsile = yn ee THE BURBANK CHERRY 119 experiments specimens growing on trees that were observed to bear earlier, even if by only a few days, than other kinds. To come at once to the sequel of the story, I was able after many years of experimentation to produce a fine, large, productive cherry that ripens about two weeks earlier than any variety before grown. This result was achieved by per- sistent selection, generation after generation, of specimens that manifested the early-fruiting character. But the full bearing of the story can- not be understood unless attention is given to the almost numberless complications that were involved. SEEKING Many Ewnps at ONCE Had the only object sought been the produc- tion of a cherry that ripened very early, it would not have been very difficult to attain success. In that case all other qualities could have been disregarded, and attention given solely and ex- clusively to the question of time of fruitage. The cherries that ripen earliest each season being selected, presently a race of early bearers would have been produced beyond peradventure. Se- lection carried through a comparatively small number of generations would have sufficed to give me what was sought. 120 LUTHER BURBANK % But a moment's reflection makes it clear th there would be no commercial value in a cherry that ripened earlier than its fellows, unless this cherry combined with the quality of early ripen- ing other qualities of size and abundance and fitness for shipping that give the cherry its value — as a market fruit. It is obvious that in selecting — these cherries it was constantly necessary to bear — in mind not merely one quality but several quali- — ties, and it requires no great knowledge of plant — experimentation to see that this aero plicated the problem. DiversirieD QUALITIES Requirep be ae In point of fact, the qualities that are required in a really satisfactory commercial fruit are much _ more diversified than the ordinary observer would q 3 ever suspect. In the case of the cherry thefe ane/l asi 4 dozen quite distinct qualities, which might be — spoken of as unit characters, that must cot A stantly be borne in mind. A cherry that will bring a good price in ie a market must be large in size; it must be attrac- — tive in color; it must be sweet and savory to the taste; and it is of prime importance, particularly from the California standpoint, that the fruit shall be of such texture and quality of skin as to — ee ee THE BURBANK CHERRY 121 bear shipment across the continent, and so reach the Eastern market in good condition. As much as this will be obvious to every eater of cherries. _ But from the standpoint of the fruit grower, there are many other qualities that are no less important. It is necessary-that the tree that bears the cherries shall be hardy and able to with- stand ordinary frosts; that it shall have the quality of vitality that makes it fairly immune to the attacks of insects; that it shall have abun- dant foliage to protect the fruit from the sun and birds; and that it shall be a prolific bearer no less than a bearer of fruit of marketable quality. All this, and more, in addition to the quality of earliness of bearing to which reference has al- ready been made. If we add that there are certain minor quali- ties to be borne in mind, such as the question of length of stem, number of cherries to the cluster, and tendency of the fruit to cling to the stone in one case or leave it readily in another, an inkling will be gained of the complications of the prob- lem in heredity that confronts the developer of an improved race of cherries. But the full significance of these complications can scarcely be appreciated wholly by anyone 122 who has not been confronted by them in actual , practice. me uF have boon able 45 Guanine nnn in a relatively brief number of years, it is — because I have worked persistently, selected — with discrimination, and invoked the aid of — the bees in making experiments on leans 8 scale. de De. wk " The modern student of heredity, in dealing : with cases such as this, is able to give a somewhat — tangible illustration of the difficulties involved — with the aid of simple mathematics. He does — this on the basis of the Mendelian interpretation — of the method of transmission of unit characters _ of which we have learned something a sre : Tue ComPLications ILLUSTRATED ane It will be recalled that we had occasion Seema sider such opposing traits as blackness and — whiteness in our white blackberry, large size and dwarf size in the case of our walnut trees, stone — fruit versus stoneless fruit in cases of our plums, — and perfume versus lack of perfume in cases of — the calla, as pairs of unit characters that are — mutually exclusive in case of any individual, but — which both tend to recur in the second generation of hybrid offspring. THE BURBANK CHERRY 128 It will be recalled, too, that a specific illus- tration of the formula according to which such recurrence takes place, was found in Professor Castle’s experiments in crossing a black guinea pig with a white one; in which ease, although all the offspring were black, the quality of whiteness reappeared in one- fourth of the descendants of the second filial generation. Now it should be observed that this ratio of one in four is a ratio that has been found to hold good in a very great number of experiments applied to various races of animals and plants, when a cross has been made and a record kept of the results with reference to a single pair of unit characters, such as blackness versus whiteness in the case of the guinea pigs. In such a case, where the offspring of the second filial generation are interbred, it has been clearly demonstrated that, on the average, one- fourth of the offspring of the second filial generation will resemble the paternal grand- parent, and one-fourth the maternal grand- parent; the remaining half being of mixed heredity. Stated otherwise, there is an even chance that in any group of four offspring of the second filial generation, one individual will resemble each Applying thls rue to the ant ol and considering for the moment only the matter — of early-bearing versus late-bearing, it should — result, if these qualities constitute a pair of unit — characters, that by crossing an early-fruiting — cherry with a late-fruiting one, the descendants — of the second generation would show one speci- men in four growing early fruit, one in four growing late fruit, and two of mrp tendencies, : {All that: would then be required waalll cin breed exclusively from the one-fourth that were — early bearers, destroying the three-fourths that — lacked ‘this quality (or tel ae undesirable quality. Not so Simpie my Actua. Worx age 3 But, unfortunately, the simplicity of the formula vanishes as soon as we come to consider — a second, and third, and fourth paket ae characters. 7 Here also the formula has been worked. os 4 in mathematical terms; and it appears that when — several characters are involved, we at once come — to deal with numbers that are no longer easy — to keep track of. Moreover, the various pairs — THE BURBANK CHERRY 125 of unit characters may be juggled in an almost infinite variety of ways. We are seeking, for example, (Q) an early- bearing cherry of (2) good size, (3) fine color, (4) sweet taste, and (5) good keeping quality. Suppose, for the sake of argument, we con- sider each of these to constitute, as contrasted with the opposite condition, one member of a pair of unit characters. Then it appears that, according to the theory of chances which underlies the interpretation of the Mendelian formula, the probability that any given combination of these five qualities will appear in an individual specimen of the progeny of the hybrid generation is only one in about five hundred. We shall have early bearers that are of good size and taste, but lack shipping quality; other early bearers that are good shippers but lack size or quality; yet other specimens that have size and taste and shipping quality, but lack the quality of early bearing; and so on throughout all the possible combinations of five pairs of qualities. But the combination of all the desired char- acters in a single individual will take place very rarely indeed. consideration, the number of possible combina- tions among them increases at an alarming — geometrical ratio. peu It appears that whereas there is | chance, when only a single pair of qualities was — in question, of producing one offspring like each — parent in each group of four; and whereas there — is the same even chance of producing one off- — spring like each parent in every group of 256 . individuals when four pairs of unit characters — offspring like each grandparent only in each | group of more than a million progeny! Quantity Propuction NECESSARY —C | Such a computation, as made in accordance — with the Mendelian formula, in itself serves to supply a ready answer to those Mendelians who have questioned the necessity of making experi- — ments on the elaborate scale that I have all along THE BURBANK CHERRY § 127 followed out. According to strict Mendelian reasoning, it is clear that we must deal with thousands of seedlings in order to stand a chance of securing a single one that shows a desired combination of qualities, when six or eight qual- ities are in question—and I seldom work with less than twice this number in view. And the case is even more complex than this computation would show, because I am always concerned not merely to combine a half dozen or a dozen desirable qualities, but to have a wide range of choice among numerous individuals showing this combination, that one may be found which exhibits the desired qualities in the swper- lative degree. It is fair to assume, then, that I should never have secured the Burbank Cherry, and following it my newer varieties of cherries that: (1) fruit weeks before the usual cherry season, and (2) produce a superabundant crop of fruit of (3) the largest size, (4) best color, (5) firmest texture, and (6) finest quality; growing in (7) easily gathered clusters on (8) trees of fine shape that are (9) hardy and (10) immune to the attacks of insects, had I not extended my experi- ments far beyond the narrow limits of hand pollination, with the aid of my hosts of indis- pensable helpers, the bees. CHERRY aye fh ih hie shows the ottval is ana ance of one of my cherie elled the “Abundance.” Like the is the product of crossing various highly developed ers of the cherry colony. 1 do not taiodmee=- a new fruit unless it is equal to any existing variety in all its qualities, tite superior to any other in at Teast one quality. The “Abundance” | herry fully meets these conditions, we eminent quality being its habit of ea sg and prolific bearing. In size it is also notable, as the illustration shows. THE BURBANK CHERRY 129 So the biometric computations give fullest support to the practical methods that I have employed for the past fifty years. _ Meantime, the results of these experiments— proving the possibility of segregation and re- assembly of these diverse qualities — give vivid illustrations of the fundamental truth of the theory of unit characters, if these be properly inter preted. Goop Fruit From BaD ANCESTORS As a further illustration in point, note this curious circumstance: I have in various instances used as a pa- rental stock, for purposes of hybridization, a cherry that produced a totally worthless fruit. The object of this selection was to intro- duce into a developing strain of cherries some good quality — say prolific bearing — that the otherwise worthless cherry exhibited in high degree. The immediate progeny of this cross would be of no value as the bad qualities of the worthless cherry were dominant. But among the remoter descendants I have been able to discover indi- viduals that combine the quality of prolific bearing with the good qualities of the other parent stock, and in which the undesirable qual- Vol. 2—Bur. E 130 LUTHER BURB ANK ene " ities of the original worthless ancestor were E quite eliminated. | Tt must be ‘clear that ‘thi wenill(aaenaa heve been brought about’ if the various pairs of plasm of the hybrids in sucha way. thal thereat characters could be sorted out and pad good quality transmitted unimpaired by its contact with the opposing bad quality. in:cther word had tiene hoon na traits in the sense in which the older experi- menters imagined the traits of hybrids to be blended, we should have had at best a cross which the qualities of the worthless cherry were mingled with thosé of the valuable one; a race which, if better than its worthless —o worse than its valued one. (Aid: it/smnight: never: daxve~been saan breed out altogether the undesirable qualities that the original cross had introduced. et 5 8 SEPARATING THE TRAITS ist: we Ihave sceh in the! caseo seahinaa as we had previously seen in the case of some other plants, and as we shall have occasion to see in numberless others in future, that it is possible THE BURBANK CHERRY 181 to breed traits into a hybrid strain, and then breed them out again. In point of fact, no progress in the production of new varieties could have been made in my experiments, were it not for this possibility. The Shasta daisy, for example, is not inter- mediate in size between the species from which it sprang, but larger than any of them. The white blackberry is not intermediate in color between the parental strains, but is of a far purer white than its light-colored ancestor.. The stoneless plum is more stoneless than the race from which it sprang, although that race has been crossed again and again with strains of plums that invariably produce a stony seed covering. Some of my hybrid walnuts are far larger than either parent stock, and some are far smaller than either. And so on throughout the list of the hybridizing experiments through which the new races of plants have been developed at Santa Rosa. Everywhere we find evidence of segregation of unit characters and recommin- gling and reassortment in later generations. Nowhere else, probably, can there be found such an aggregate mass of testimony to the operation of this principle as will be supplied in the pages that tell of my various experiments. 132 + LUTHER BURBANK And, reverting to the cases in hand, there is’ no better illustration of the truth of this propo- — sition than that furnished by the new cherries — which present, in a single individual, ten or a dozen clearly definable qualities that have been _ sorted out and brought together from the com- mingling of widely divergent ancestral strains. — The traits that were developed through — response to the environment in widely scattered _ geographical territories and through hundreds — of generations, have been brought together, in 2 combinations never hitherto presented; with the — result that my early-bearing, large-sized, bright- _ colored, and highly flavored cherries constitute essentially a new variety of fruit, while at the — compassing influence of the laws of heredity. eat ee Pa According to strict Mendelian reasoning, it is clear that we must deal with thousands of seedlings in order to stand a chance of securing a single one that shows a desired combination of qualities, = =—— when six or eight qualities are in question—and I seldom work-with less in view. SA en ae Ba SAE ee ie Fr Pee ee ee eee ep eee P| ee ee THE SUGAR PRUNE How a Tree WaAs CHANGED To FIT THE WEATHER ROBABLY you have heard the story of the general who declared it impossible to build a bridge across a certain stream that obstructed the march of his army until he had plans and specifications and blue prints for the work. While he waited for these—so the story goes—a subordinate built the bridge, and re- ported to his superior with the suggestion that it might be well to march the men across the bridge forthwith and then make the drawings at leisure afterward. A visitor at my orchard told me this story, and applied it to the case of some of my newest varie- ties of plums. “It appears to me,” he said, “that your custom resembles that of the young soldier who built the bridge without the plans and specifications. You appear to have developed a good many of your fruits on the same principle. You seem to have 133 134 LUTHER BURBANK ~~ gone ahead and produced the fruit, while a more cautious experimenter would have been occup in designing hybridizing methods and testing unit characters, and would not have been fully prepared to start on the actual constructive work until about the time you finished.” Whatever the force of this comparison, it is true that I have often succeeded in producing a fruit of the finest quality by methods that t a less practiced experimenter ‘might look hapha ard; methods that did in point of fact lack some- thing of the precision that an investigation eon- ducted solely for purposes of scientific record rather than for practical results might have Such is the case with a large number of ex- periments in plum breeding. Here I have dealt with such vast numbers of individuals and brought into the hybridizing tests such varied and so many races, that accurate record of every step of a series of experiments extending over a term of years was quite out of the question. 4 My “Combination” plum has a pedigree that includes strains of almost every race of plums under cultivation. From the seed of this strange hybrid you may produce trees that will bear fruit closely similar in all respects to at least a score of entirely ae ee ee ee tr THE SUGAR PRUNE 135 different well-known varieties or races of plums. The mixed pedigree of the product is recorded in this motley galaxy of offspring; but details as to all the parental crosses, tracing back along an experimental search of thirty years’ duration, are not to be had. The original parents used in the first cross are of course known; but successive generations deal with tens of thousands of seed- lings. So it was impossible for anyone who was carrying out, as I have been, not less than three thousand different plant-breeding experiments each year, involving in the aggregate not fewer than six thousand different species, to trace ac- eurately, much less to record, each and every cross-fertilization among the myriad blossoms of my orchard. Yet a chance hybridization might by some good fortune effect precisely the needed combination of qualities to produce a fruit that had long eluded my most earnest efforts at systematic breeding. But by my very extensive and varied experi- ence I can judge from the result what the racial strains most probably were that were blended to produce the new hybrid. But even this is not always possible, and not a few among the thou- sands of new varieties of plums that have orig- inated on my farms are of untraced and untrace- 186 LUTHER BURBANK able pedigree, at least as regards some of th When I say tint event ee SEU half million seedlings of the plum have passed under my hand and eye in the course of my many series of experiments in the perfection of this fruit, the reader will not wonder that there are Bape in the-recond, Otherwise thee ae records not plums. “ok Dirricuttires [yvo.vep On the other hend, it must be cnniheliaa a there are almost numberless instances in which the hybridizing of different strains of plums has been effected by hand, in accordance with the most rigid scientific methods, and accurately recorded in my plan books. Indeed, this is true in almost all cases of the first cross through which a tendency to variation has been brought about. The first generation hybrids are usually very much alike, and inspection of them often gives no clues to the ultimate results to be expected. But in the next generation all the divergent char- acteristics of both racial strains strive for repre- sentation, and the diversity of forms produced may baffle anything like accurate description. Beyond this stage it is usually necessary for the practical breeder to turn over the task of THE SUGAR PRUNE 137 cross-fertilization to the bees, contenting himself with keeping a sharp outlook for seedlings that show desired combinations of traits. How diversified these traits may be in case of a market fruit has been illustrated at some length in the preceding chapter. In this respect, most plums are at least as complex as the cherry, and the requirements in the case of the sys prune are even more exacting. The word prune, it should perhaps ie ex- plained, is applied in California to any plum that can be dried with the stone in place without fermentation of the pulp. The quality that per- mits such drying is largely dependent on the amount of sugar that the fruit contains. There are prunes and prunes, as even the most unprac- ticed observer must know, and there are grada- tions of size, flavor, and sugar content that are vastly important from the standpoint of the or- chardist and by no means without interest from the standpoint of the consumer. One of the tasks I early set myself was to pro- duce a prune that should excel all others in the qualities, singly and combined, that make for per- fection in this valuable fruit, and there can now be no doubt but that this end is fully accom- plished, although I shall not say that my com- plete ideal of a perfect prune has thus far been to ative dan, ao anhinsen sana a It is a matter of record that the prune was originally introduced into California by a French sailor named Louis Pellier, who came to San reached. The most important of the varieties of prests thus introduced was the common French prune, sometimes known as the prune d’Agen. The descendants of this stock made up the large prune orchards of California for the ensuing half cen- tury. THE SUGAR PRUNE 139 The French prune, while not without its good points, is by no means a perfect fruit. It is a clingstone, which is a serious defect in a prune. Moreover, the stone itself is rather large in pro- portion to the flesh. The fruit ripens too late to be profitable in some parts of the country, and the risk of having the crop destroyed by the early rains is a serious defect everywhere. Neither is the tree a strong grower, or a very reliable producer, or of the most symmetrical growth. It occurred to me, therefore, when I first took the matter in hand, that among the essential qualifications of the ideal prune at which I must aim would be early ripening and the production of a larger, still sweeter freestone fruit -that would be borne in profusion. THE IDEAL PRUNE We have had occasion to point out that the commen orchard fruits do not breed true when grown from the seed. Explanations of this fact have been given, and fuller explanations will ap- ‘pear in subsequent chapters. Here it suffices to note that the prune is no exception to the rule. Very seldom does the seed of a prune tree pro- duce a fruit that much resembles the prune. . onbeciiia THE SUGAR PRUNE AND ITS PARENTS pi FOS Te ge Rae The § Prune was developed by . selection from a cross between | ee French prune and the Hus however, manifesting, also, a most un- i vigor. The French prune is still: Hes # largely grows in | California, but this: ae. must ultimately displace it. fet THE SUGAR PRUNE “141 Usually the fruits are of all sizes, shapes, and colors. They are sweet, sour, bitter, as the case may be. Some of them crack and others remain smooth. The trees on which they grow are many of them ill-shaped, weakly, or subject to disease. Although the parent form may have been an early ripener, the seedling may produce fruit that ripens so late as to be useless. All of which serves to give an inkling of the difficulties that beset the plant experimenter who sets out in pursuit of an ideal prune. Moreover, the variety of characteristics re- quired to make up the ideal prune is far greater than the novice might suppose. It is a matter of course that the fruit should be large and well flavored—though not too large, lest it become too difficult to dry; and that it should be produced in abundance. But there are various equally essential points that the novice might overlook. There is, for example, the matter of quality of skin, determining the fitness of the fruit to un- dergo the lye bath which is an essential part of prune curing. It is necessary to dip the prunes in this bath, consisting of a solution of potash or lye, in order that the skin may crack in such a way as to per- mit the rapid evaporation essential to quick dry- 142 LUTHER BURBANK _ ing. But, in a very large number of cases, prunes that have every other essential quality fail when subjected to this final test. It is not too much to say that I have developed hundreds of new varieties of prunes that were well nigh perfect as to quality, but which had no commercial value Whatever because they: failed to staataae amma or to be literal the alkali-test. So the experimesiter is always cbufeedsed/iel the possibility of failure at the very last, even when his efforts seem to have met with complete success at the earlier stages. With the utmost solicitude, therefore, he must watch the fruit as it passes through the potash bath. If the skin peels from the fruit instead of dracking, that partioular variety 9 aEREeanE matter what its other good qualities. 7 Moreover, the cracks in the skin must be very smal] and numerous. If they are too far apart by the hundredth of an inch the prune will have a rough appearance that mars it from the com- mercial standpoint. If the skin is too thin, so that in gathering and handling the fruit is bruised, it can never make a commercial prune. But, on the other hand, the skin must not be too thick as then it would not be properly cut by the lye. In a word, there must be the most nicely balanced qualities of the skin of the fruit, and THE SUGAR PRUNE 148 without this final touch the prune is a failure, even though it grows to seeming perfection on the tree The intrinsic qualities, in addition to perfection of skin, that I aimed at from the outset, were large size, increased production of sugar, and early ripening. The matter of size is doubly important because this largely determines the price that a prune brings in the market. The sugar content is ob- viously important because upon this chiefly de- pends the drying quality of the fruit. And the matter of early ripening is at least as essential as any other quality, because the prune is dried in the sun, and the fruit that ripens late in the season, not only often lacks sunshine to complete the process, but may be absolutely ruined by the rains which begin to fall in the early autumn. How I AcHI£veD SUCCEssS When I began the quest of a perfect prune, in the year 1879, it at once occurred to me that something might be accomplished by hybridizing the French prune with another variety known as the English Pond’s seedling but usually called in California the Hungarian prune. This was a large and handsome fruit, while the French prune brought to the combination the qualities of 144 LUTHER BURBANK rich flavor and relatively high euguriitctelan. | If these diverse qualities could be combined in a — single fruit, I saw that a great aie made. ee The little French prune was ohana mother tree and many thousand blossoms were _ hand-pollinated from the Hungarian. The offspring of this cross were as variable as had been expected, and among the seedlings were _ some that produced fruit of superior quality. — Four years later, at the meeting of the California _ State Horticultural Society, I had the pleasure of exhibiting no fewer than seventy varieties of the most promising of these crossbred seedlings. And in 1898 two new plums were introduced as _ representing the hestealersion Sasa 7 myriad forms of the hybrid progeny. = One of these new plums was named the Giant, the other the Splendor. The former is a handsome plum priactiontigt ta termediate in qualities between the original parents. It has peculiar value as a shipping plum, and in particular it gained popularity with the canners because its skin has the property of rolling away from the fruit when placed in boil- ing water, leaving the rich, honey-colored flesh. But these, of course, are not the qualities desired in the prune. THE SUGAR PRUNE 145 The other variety, named the Splendor, is about ene-third larger than the common French prune and contains something like 5 per cent more sugar; its quality and flavor are also superior. It has, moreover, the drying qualities of the prune, and it was freely predicted by - many who knew it that it would soon completely displace its French progenitor. But unfortunately it had one single peculiarity that placed it at a disadvantage; namely, the propensity of the fruit to cling to the tree when ripe. It dries into a first-class sweet prune, but it dries on the tree, and that is an insuperable de- fect, because the prune grower demands that the fruit shall fall naturally to the ground. He does not wish to be obliged to take the trouble even to shake the tree. So the unfortunate propensity of the new prune to hold to its moorings, so to speak, greatly marred its value. At Last A SUPERLATIVE PRUNE In the year 1899, however, after almost twenty years of continuous and laborious effort, I was finally able to present a prune which met the expectations of the most sanguine; a prune which combined all the good qualities of its progenitors 146 LUTHER BURBANK and combined them in superlative degree, and quality of ripening about the first of August, two eo'mane weeks in ‘nevada ee the prune harvest. Tho -clancet ‘perfect. pratie!nae/ Sanna market in 1000 nde he ee Prune. ee ing A description of the new fruit was aia by Mr. B. M. LeLong, secretary of the California State Board of ee - follows: The Gager prime is dn extremelppeiulieiaadiie ripening August 1; it grows superbly with yellow flesh, tender, and rich in sugar. The skin is very delicate, at first of a light purple tinted with — green, changing at maturity to dark purple, cov- __ ered with a thick white bloom. The form is ovoid, — slightly flattened, measuring five by six and a half inches in circumference, average size fifteen to a pound, which is two or three times larger than the French prune; the fruit stalk is short, and severs very easily from the stem as the fruit reaches maturity; the pit is of medium size, flat- tened, slightly wrinkled and most often separated from the flesh; the skin is so thin or porous that the fruit begins to shrink on the tree as soon as ripe.” THE SUGAR PRUNE 147 To add to the value of the Sugar prune, the tree on which it grows is unusually vigorous and astoundingly productive; in fact, almost to a fault. Analysis of the fresh fruit at the State Univer- sity discloses the fact that it is nearly one-fourth sugar—the exact amount being 23.92 per cent, contrasted with the 18.53 per cent sugar content of the French prune, and the 15.383 per cent of prunes in general. Not only does the Sugar prune contain far more sugar than any of the varieties from which it sprang, but it fully equals the French prune in flavor, and it is two to three times as large. It is far more productive, and can be grown for one- third to one-half the cost of producing the French prune. In flavor it is fully equal to the celebrated Imperial, and, in most striking contrast to that fruit, it is exceedingly productive. Add that the new prune excels al] other vari- eties in the extreme earliness of its time of fruit- ing, and it will be obvious that the Sugar prune marks at least a long step toward the ideal at which I aimed. It ripens at a time when the weather is hot and dry, so that it can be rapidly cured. A week or two later when the other varie- ties are maturing, the weather is often foggy and cloudy and sometimes even rainy, so that fruit 148 LUTHER BURBANK curing is earried on under diffculties and often with serious loss. : Sewtes eet It is not strange, then, thet the Sugar grand met with an immediate and enthusiastic welcome from many fruit growers, although of course there were regions in which a prejudice was shown against it, such as always ee : product. In the markets of the Kast, the damnit Saati q Sugar prune was soon far in et ti ah LEAVES OF STRave ERY: i: aes : RASPBERRY HYBRIDS _ The strawberry-raspberry hybrids had leaves which were uniformly ri 4 foliolate, but which varied greatly in “a - size and shape. Characteristic samples of the different forms are here shown, Tt was pe culiarly to be regretted that — at the hybrids were not fertile, as a new and highly interesting form of Ls, been possible to establish a owe race combining the strawberry and the raspberry. hot INTERESTING FAILURES 175 effected. The raspberry was selected as the pistillate plant, and pollen was necessarily ap- plied from whatever strawberry was at hand. It was impossible to choose as to the latter point, for the strawberry is for the most part out of season when the raspberry blossoms. Such material had to be used as could be found. The pollination -proved effective, and the raspberry plant produced a full crop of fruit, There is no very marked immediate effect observable from such hybridization, The pulp of the berry seems not to be affected; but the essential seeds within the berry are enormously modified, as the sequel showed. For when the raspberry seeds were planted in the greenhouse, the young hybrid plants that come up in pro- fusion had all the appearance of ordinary straw- berry plants. No one who inspected them casually would suspect their hybrid origin. The raspberry, the pistillate parent on which the seeds had grown, has leaves with five leaflets. But there was no leaf of this character among all the hybrids; without exception their leaves were trifoliolate like the leaf of the strawberry. In other words, in the matter of foliage, the strawberry plant was entirely prepotent or domi- nant, and the characteristics of the other parent were latent or recessive. depart from the habit of the strawberry. To close inspection it might appear that the main stem was unusually thick, and that the leaves were a little more wrinkled than is usual with the strawberry, and their edges slightly more — serrated. But aside from this, the hybrid plants were in appearance true strawberries. About the first of June, however, the plants began to throw out underground whereas strawberry runners are normally on the surface. These stolons suggested roots of the raspberry, yet the new plants that sprang from them here and there were exactly like 1 strawberry plants. So at this stage it would seem that the influence of the mother parent had been but slight. But along in July came the transformation. Rather suddenly each main plant sent up two, three, or more strong smooth canes, which grew to the height of from two to five feet. These canes were absolutely thornless, as were all other portions of the plant; they were as smooth as strawberry plants in leaf and stem, but their form and manner of growth now departed INTERESTING FAILURES 177 strangely from the traditions of the trailing parent. . Obviously the influence of the raspberry parent had at last made itself potent. Some of the plants were yellowish, indicating that the berries would probably be yellow; others were reddish. There were no blossoms the first season, but the ensuing year clusters of blossoms of great size were put forth, some of the bunches being twelve inches in breadth—far larger than those usually seen on the raspberry. In asingle cluster there were sometimes several hundred flowers. The individual blossoms were gener- ally larger than the flowers of the raspberry, but slightly smaller than those of the straw- berry. In the center of each blossom was a miniature berry, which might be said to resemble either a strawberry or a raspberry, being so small that its exact characteristics could hardly be dis- tinguished. I was quite sure I had a valuable cross, and that at least one might be found among the many that would produce fruit. But in this I was disappointed; not a plant produced a single seed. The miniature fruit remained unchanged in size until it finally dropped from the bush in the fall. 178 LUTHER BURBANK The following season a. few ol Aianmnaada one or two fruits having two or three drupelets each, like mere fragments of a normal raspberry. — But not a seed was found, The plants were as — sterile as mules. So here the experiment ended, and the hybrid strawberry-raspberries — the hybrid Gewberries to the brush. Ramee | Whuy THe EXPerrmMents Faun — If we now consider the vonults of Wiaeeaual : experiments, it will be clear that they have — certain elements in common. In all cases the — hybridizing was effected between species that are botanically related. But in no case was the relationship between the mated forms very close. Ann ies feck sf Oe ee in enabling us to comprehend the results, | It is almost axiomatic to say that the hybrid- izing of plants generally becomes increasingly difficult in proportion as the attempt is made to cross more and more distantly related species. — Even within the same genus it is very often impossible to produce a hybrid that is not sterile. | I might cite in further illustration of seed difficulties the experiments through which I have — hybridized the apple with the pear, and with the | quince; the cherry with the plum; and the peach — Sa iz INTERESTING FAILURES 179 with the almond, with the Japanese plum, and with the apricot, without in any of these cases producing a product of value. These crosses, like the ones just detailed, bring together racial tendencies that are too widely divergent to be harmonized. It would appear that it is essential to the differentiation and perpetuation of species that bounds should be set on the possibility of pro- ducing a disturbing influence through hybrid- ization. When plants, even though sprung from the same origin, have diverged so widely and for such periods of time.as to produce forms differ- ing from one another so greatly as, for example, the mountain ash, the apple, and the rose differ from the dewberry; or the strawberry from the raspberry—it would seem not to be of advantage to the plants to combine these forms. The changes that would be produced, were such hybridization to result in virile offspring, would perhaps be too divergent to fit into their environment successfully. At all events the possibility of such crosses would constitute a disturbing influence of organic nature at least in some of its orderly character. And so it appears, so far as may be judged from these experiments, that even when hybrids between these divergent forms are produced, the 180 offspring are generally sterile, and ie rests of the hybridization are not perpetuated. Such, then, is the barrier that nature press the interest of rece pecbetysticay San that have already widely diverged. __ But, on the other hand, we have seen many | illustrations of the fact that when species a little — more closely related are hybridized, the result may be not to produce sterility butto' Gwe mies virility to the offspring. | We saw this illustrated, for example, ns : the walnut of the eastern United States was crossed with the black walnut of California. The hybrid progeny not only exhibited tremendous individual vitality, growing with great rapidity and to enormous size, but they produced an altogether extraordinary abundance of fertile fruit. The hybrid variety thus produced--siiill it will be recalled, the “Royal”—constitutes a new race that can more than hold its own against the parent forms, And the reason for this seems to be that the two species of walnut had not become sufficiently divergent to introduce a greater diversity of conflicting tendencies than is consonant with racial progress when the strains are brought together. INTERESTING FAILURES 181 _ But it will be recalled that when the California black walnut was hybridized with the English walnut—producing the “Paradox”—the results in this regard were quite different. While the individual offspring showed great vitality, they were almost sterile, producing only a few stray nuts in contrast with the profusion of the Royal hybrids. And we may infer from this result that the California walnut and its remote English cousin have diverged to a point lying just on the border line of the limits of desirable racial mingling. These limits have not quite been crossed as they have been in the case of the dewberry and apple tree, and the strawberry and raspberry, but they are being approximated; and there is no probability that the hybrid offspring of the black walnut and the English walnut could maintain itself through successive generations as a new race in the state of nature. At all events, its prospect of success would be a doubtful one. Tuer APPLICATION TO THE HUMAN SPECIES It is more than likely, then, that the lessons taught by the unsuccessful experiments recorded in this chapter are quite as important as if they had led to what might appear to be more practi- 18g «= LUTHER BURBANK on cal results. For they serve to emphasize a great 7 fundamental truth of heredity, which has a more important bearing on the problems of racial — development of all organic beings, including — man himself. It has become more and more clear in recent years that the underlying prin- ciples of evolution apply to plants and animals — alike, and that much may be learned about the better breeding of mankind from a direct study of the breeding of the lower organisms. = And as regards the particular case under con- sideration, it is scarcely to be doubted that we may draw important lessons from the obvious results of the hybridizing of plants Sr seein the commingling of human races. > Tt is commonly hheld thet the various siheilal oF races of man constitute a single species. But — this classification was made under the influence of the old idea that sterility of offspring isa valid test of specifie difference. No one nowadays — holds that view, with regard to plants at any rate, and the view is probably no more valid in its application to a great number of animals, in- cluding man himself. But, in any event, the question as to whether mankind constitutes a single species or several species is a matter of definition of no real impor- tance. It is beyond question that the human INTERESTING FAILURES 1838 family comprises widely divergent races, and it is scarcely open to question that the divergences in many cases are so pronounced as to make hybridization between these races inexpedient, even though still possible. The student of history tells us that the great civilized races of the past were all mixed races. This was true of the Egyptians, the Babylonians, the Greeks, and the Romans. It is true of the chief nations of .to-day. But the races that intermingled to produce the great peoples have always been somewhat closely related. No permanent good result has been generally achieved, for example, by the commingling of Mongolian and Aryan blood, or of Aryan with Negro. Such wide crosses must be expected to produce at least a measure of infecundity, and a commingling of racial tendencies too divergent to be advantageously blended. The case is comparable to that of the Paradox walnut, even though it be not quite so extreme as the case of the hybrid strawberries and dew- berries. But what chiefly concerns us now is not the past history of mankind, but the present and future history; and in particular the history of mankind here in America. There is taking place 18§ LUTHER BURBANK — in our day what is doubtless the greatest migra- tion in all history. The races of Europe are — flooding into America, and there is a more pro- taking place on our soil than perhaps ever occurred in any one place, or in any single epoch, in the history of the world. America owes its present greatness in consid- erable measure to the mingling of moderately divergent strains in the past; but this fact should not blind us to the menace that lies in the mingling of races that are too divergent to blend advantageously. It is this thought that I would put forward as the most important suggestion that arises from the study of the hybridizing experiments which were unsuccessful in blending the hereditary tencensiies vot 'coetalas rocks ‘of eee too widely divergent. PLANNING A NEW PLANT THE First STEPs IN PRACTICAL WorK ITH many examples of the actual work before us, let us now proceed to investi- gate some of the interesting details of the methods, treating the subjects of pollination, grafting, plant affinities, fixing traits, selection, and spreading before us all of the processes which have been employed in more than 100,000 sepa- rate experiments. The purpose has been to lead the reader, by easy and interesting stages, up to a point where a delineation of the actual processes may be most readily grasped. This will complete the consid- eration of general methods and, with the two preceding descriptions, give us a more intelligent survey of the work. Some one has said that an artist is a man who can see the picture in the landscape. In similar fashion it may be said that a success- ful plant experimenter is one who can see new 185 186 «=©9LUTHER BURBANK varietieg of feture plants when ia au: uae 4 existing varieties. But of course the painter, whatever bis ome structive imagination, does not always see at 1 first glance every detail of form and color that will ultimately appeal to him. Nor can the plant experimenter claim, by any manner of means, to 4 know always from the outset just what his new plant creations, as a result of these new combina- tions, will be like. There are numberless in- stances, indeed, in which a plant experimenter who operates on a large scale may make various ] experiments in the combination of different — species and varieties of plants; but, on the other hand, it is necessary in the pursuit of practical plant developments to have a tolerably precise idea im mind as to the) pextieeeh ee which progress is desirable. Lacking such an ideal, the breeder of ‘plants a would be about as likely to produce new creations of value as an architect would be likely to con- struct a fine building by putting materials to- _ gether at random without a carefully precon- — ceived plan. ‘The mind of man has sounded no linaits 60 ‘ines 4 or space and is learning that all the varied forms and conditions which we know are intimately connected and interdependent upon past condi- a gs de eat OR oe: Ee | ee ee ee | ae PLANNING A NEW PLANT 187 tions which have shaped their course and struc- ture. The ever-varying influences of environ- ment which have surrounded plants, animals, worlds or atoms have molded their characters and tendencies into their present condition. This we may call heredity or stored environment. The more permanent aggregations with which we are familiar, like rocks, metals, air, water, and hundreds of others, seem very uniform and fixed in their characters, while, if chemically combined into the forms of animals or. trees, they are quite able to vary before our eyes in aspect, habits, and characters in order to adapt themselves to the varying conditions of life; if plants and animals were not more pliable and alive than rocks and metals, they could not exist. Even the apparent qualities of most chemical combinations which seem arbitrarily and perma- nently fixed may, when combined and placed under certain environments, develop unsuspected characters and tendencies. Everybody knows, for instance, that the char- acters of iron are more fixed than those of plants and animals. The characters and habits of iron, lime, soda, and hundreds of other chemical sub- stances and compounds can be fully depended upon; they will always act according to their in- COMPLETE KIT OF. IZING TOOLS This shows all the Pe for elaborate experiments in cross-fer- tilization. The scalpel is used some- — = times to cut across unopened een A : | —for example, apple blossoms—in such — ae a way as to remove the pollen-bearing CL anthers all at once. Where the formof the flower does not permit this, the — wee pincers are used to pluck out the sta- — mens. The watch crystal is used on which to collect pollen, which is trans- ferred to the stigma of another flower, —__ either with the finger tip or with a . camel’s-hair brush. The other imple- _ ments are sometimes required to manip- ulate a flower of peculiar form. The magnifying glasses are needed only with very small flowers. The use of the ‘i paper bags is illustrated elsewhere. The cardboard labels are to record the _ experiment. | PLANNING A NEW PLANT 189 herent qualities, but the chemical substances from _ which animals and plants are formed are so numerous and in such diverse combinations that their behavior is vastly more complicated and un- certain. : The structures which we call plants and ani- mals make use of the chemical combining and separating forces of nearly every substance so far discovered in the universe. Nature has been carrying on selective world- wide breeding of plants and animals on a con- stantly widening scale for millions of years; but nature does not care for sweet corn, melons, Bart- lett pears; luscious, juicy, fragrant peaches; large, early, sweet cherries; thin-skinned, seed- less, juicy oranges; large grapes of many seasons, colors, and flavors; pineapples with their delight- ful aroma; prunes with sugar content sufficient to preserve them while drying; large, crisp cab- bages; head lettuce; “Quality” asparagus; self- blanching celery; double roses; varicolored car- nations; cactus dahlias or wonderfully colored gladioli; cannas and lilacs with new perfumes and a beautiful varied range of splendid color effects, _ or the farmers’ crops of varied grains and pota- - toes which now are, in most cases at least, a hun- dred times as productive and of almost infinitely improved qualities. 190 LUTHER BURBANK ot man hen ‘at fish wien anna consciously, produced all these marvelous im-— provements and ten thousand others and is now making and will make improvements in every- thing, plant and animal, which is useful to him; not by nature’s method of selective breeding for the continuance of life at any cost, but for dsfuits ‘purpose to sapply hee clothing, shelter, and luxuries. “In what percentage of cases have you achieved the ideal at which you aimed in the produstion of new variation of Seuleaet ta is asked. The question ie almost impossible of Geaalle answer. When I first commenced, doubtless a very small proportion of these experiments came — out as expected. But now, with years of experi- — ence to guide me, it may be said that I always get something not far different from what — is desired. In most cases the result comes just — about as expected. But this is because I am — working with plants that I have previously — tested. With a new plant there is sometimes doubt. — But if it is a case of poppies or walnuts, plums, 7 corn, peaches, wheat, carnations, potatoes, and a — thousand or more others that have been fully — tested, I know just about what to expect. Co Ree Peay oe Sacer Te Rear Wie: Ree Ree ee RRP ee ee RI eg 4 . , PLANNING A NEW PLANT 191 At best, however, I am very often reminded that each species has its own individuality and that even the most familiar plant may hold sur- prises in store for us. Tue RoucH SKETCH “But just how do you start out when you are seeking to create a new form of plant life?’ I am constantly asked. And here again the answer is difficult. Every- thing depends upon the ultimate object. If Iam seeking merely to test the possibilities of making certain crosses, or as it were feeling my way along new channels, it is more or less like a person grop- ing in the dark. This form of vague experimentation is often full of interest. Instances have already been given of what may come to pass when we combine plants of widely separated species or of different genera. The reader will recall the case of the petunia with the tobacco habit and of the dew- _ berry crossed with such remote cousins as apple _ and pear and mountain ash. These experiments were made without a clearly defined object—ex- cept to ascertain whether it was possible to com- _ bine plants of such diverse character. . And the results of these experiments, while of _ Very great scientific interest, were not practically 192 LUTHER B successful in a commercial wae and i primarily expected to be. eae omer, on the enee of “dead work,” in which he emphasized the fact that the main bulk of the experiments which any scientific worker must make will lead to no definite goal. A large ps of the time of every experimenter must be given up to following trails that lead nowhere in par- ticular or that end in cul-de-sacs. ee!) Apes The work of the plant experimenter is no ex- ception, but there is always an incentive to fur- ther .effort in the knowledge that a path that — seems to lead only into impenetrable mazes may presently bring one out into the light. To make the application to one illustrative case ar many: For twenty or more successive seasons I attempted to hybridize certain species of Sola- num before I finally succeeded in effecting a — cross that gave me a few seeds from which sprang a the new race of sunberries. E But it must be understood that the main bulk 4 of my experiments are not made in any haphaz- — ard manner. 4 On the contrary, my most important results q have been attained by continuing the experimen- — tation along rigidly predetermined lines and by — PLANNING A NEW PLANT 193 methods of hybridizing and selection that my earlier work had fully established. Having tested the usual limits of making new plant com- binations, I was presently able, like any other trained technician, to apply the knowledge thus acquired toward far more definite results than were at first possible. ) In the case of the Shasta daisy, the plans were all laid out beforehand as to just what type of flower I wished to produce. The ideal of a white blackberry was also, of course, a perfectly precise and definite one. Obviously the fragrant calla, the stoneless plum, the early-bearing cherry, the sugar prune, and the spineless cactus are other instances in which the ideal pursued was as clearly conceived and as definitely outlined in advance of my, earliest experiments as a cathedral is outlined in the mind of the architect before he commences his preliminary drawings. In one case as in the other the details may be modified as the work progresses, but the general idea of the structure aimed at—be it new fruit or new building—must be conceived with a scien- tifie definiteness from the outset. My original conception of a new plant creation, in the cases outlined and in a large number of others, cer- ' tainly bore as close a resemblance to the final ONE OF THE ORIENTAL PEARS The Oriental pears have not the characteristic shapes of the European = pears. The latter were presumably modified in shape through selectionata | comparatively recent period. The orig- inal home of the pear was, without doubt, central Asia, and the fruit was carried into Europe, probably in pre- historic times. The pear is often char- acterized by having a fibrous or woody — | ‘ deposit in the skin and near the core, — indicated by the dotted orn | ene this Oriental specimen. wees CNR A Sd) ee a we ee ae Oe, Ere eam i a ica a a ai i a oe 2 is he Peas PLANNING A NEW PLANT 195 product achieved as the first rough drawing of the architect ever bears to his finished plans. “But how do you begin? What is the very first thing?” : The “very first thing” I have already described —it is the conception of an ideal, a mental picture of the new plant form desired. CLUEs TO BE FoLLOWED It has occurred to me, for instance, that the cherry crop is not what it might be. I have learned that there is a steady market for early cherries and that a difference of a few days in the time of marketing may make a difference of more than one hundred per cent in the price. And so I ask myself, why not create a new cherry that shall be ready for shipping at least a week or two earlier than any cherry now in the market. Of course, an early cherry must have a number of other desirable qualities—large size, rich color, lusciousness of flavor. Knowing this at the out- set, I soon learned that it is desirable also, from the standpoint of the shipper, that the cherries shall grow on short stems. I know that the tree producing them must be hardy, capable of with- standing both cold and wet winters, and dry sum- mers, and that it must have an inherent vitality 196 LUTHER BURBANK that will make it resistant to most of the attacks > of insects and fungoid pests. Next 1 ask whet warrant tes ili aes ing that such a fruit structure can be built. And here the answer is supplied solely by the use of imagination in connection with an inspec- tion of the existing races and varieties of cherries. On examining the best fruits already in the or- chard, we find that there is a large measure of variation between the cherries grown on differ- ent Kinds.of trees, as well as betwoakane lam vidual specimens on the same tree. In imagination T-look ‘beck far Salaneaaae and inquire as to the racial history of this fruit and am led to believe that certain among the an- cestors of the cherry have grown in semitropical climates, and I know that even in the present day there are species, doubtless sprung from the same original stock, that grow far up into Canada. Why is it that the cherry shows such a propen- sity to vary? The answer is found in the assump- tion that the existing cultivated races carry in their veins, so to speak—tendencies drawn eaters varied strains of a mixed ancestry. ‘And I-know thet it should ‘be poi aaa centuating the tendency to variation through fur- ther hybridizing, and by careful combinations and selections, to attain the object sought. - PLANNING A NEW. PLANT 197 It will be obvious, then, that I am not prepar- ing to make bricks without straw and am count- ing well the materials with which I must work, just as the architect from the first stroke of his pencil bears in mind the materials of the future cathedral. We do not imagine that an apple tree can be produced from cherry trees, any more than the architect assumes that he can build a marble cathedral out of bricks; well knowing that there are sharply defined hereditary limitations be- yond which the cherry cannot be made to go within any such period of time as that limiting the experiment. In other words, I do not ask the impossible, although it has often seemed to some of my less intelligent critics that I have asked the highly im- probable. But the results attained are in themselves very sufficient answer to these critics. If my vision has in some cases been the ¢learer, it is merely that my knowledge of plant life, drawn from the school of experience, has been wider. To the uninitiated observer it may have seemed that I set no limits to the transformations at- tempted. In reality, my plan has always from the outset recognized most definite limits—al- though often enough the limits as conceived were spring hybrid off. hd f such mixed specimens 0 “ good material for the develop ck fests: PLANNING A NEW PLANT 199 quite different from those that had been set by theoretical botanists and compilers. Alm FRoM GALTON’s LAw In attempting to estimate the possibility of improvement in a given form of plant life, it is of value to recall the formula put forward by the late Sir Francis Galton; a formula often spoken of as Galton’s law. _ According to this estimate, the hereditary traits of any given organism are so intermingled that we may assume as a general rule that off- spring of a given generation will inherit about half their tangible traits from their parents, one quarter from their grandparents, one-eighth from their great-grandparents, and so on in de- creasing scale from each earlier generation. Stated otherwise, according to this rule, we should be able by observation of the parents of any given organism, to see presented half of the traits of the offspring, but we may expect that the offspring will manifest, as the other half of their inheritance, traits that have come to them through the process of reversion or ata- vism, from remote generations of the ancestral strain. And this obviously gives opportunity for the appearance of an enormous variety of traits in 200 LUTHER BURBANK : any given generation that were not manifested ia the preceding generation. Thus any given individual has normally, as a moment's reflection will show, four grand- parents, eight great-grandparents, sixteen ances- tors in the generation before that, then thirty- two, sixty-four, one hundred and twenty-eight, and so on in a geometrical ratio with each re- moter generation. So the normal ancestral clan of any one of us numbers more than a thousand different individuals within the relatively limited period of time compassed by ten generations. And, according to the estimate of Galton, to which numberless cases of atavism give force, certain traits and tendencies of each and every one of these ancestors may make themselves manifest in the personality of any given descendant. Galton’s studies, upon which his formula was based, were chiefly made with reference to hu- man beings, but we now know that the laws of heredity apply with equal force to all kinds of living organisms, including plants; and whatever the limitations of Galton’s law as a precise for- mula, there can be little question as to the general truth of the principle that he invoked. Hence the value of that search in imagination for the ancestors of our cherry in their widely mee To ee Re RT TIRE 4 RTs By PLANNING A NEW PLANT 201 separated habitats and with their widely diversi- fied traits and habits. But of course in making practical studies for the development of the mental blue print with its forecast of qualities of our new cherry, we must perforce be guided largely by the observed qualities of the parent stock with which we deal. Precisely what were the qualities of the remote ancestors we can only infer. But we can see for ourselves what are the qualities of the fruit before us. We know, then, pretty definitely what we may expect as to one-half the traits of a hybrid that will result when we cross two varieties of cherries in our orchard. The other half must be some- what a matter of conjecture, to be revealed by the actual product or, as is practically the case, by succeeding generations. What we actually do, then, in practice, is to take pollen from a variety that has been observed to bear fruit somewhat earlier than neighboring trees, and with this pollenize flowers of other varieties that have been observed to produce fruit of exceptionally good quality. Pollination accomplished, by the method elsewhere described, we can only mark the branch and the individual fruits so pollenized for future identification, and await results. TEN CORN VARIATIONS _ The smallest figure, at the lower left, | shows the grain of an improved teosinte, the primitive type of corn. It has no- rachis or cob, the kernels uellng oe : like wheat. The other figures fet A ! few gradations from this primitive to field corn, as developed through selec- , tion. We may suppose that eli passed through some such stages as these in the course of its long evolution- : ary development. SF ae epee Sean hy PLANNING A NEW PLANT 203 The seed thus secured will be planted next season, and in due course we shall have a seedling which, when grafted on another tree to speed its maturing, will come to blossoming time—after another period of waiting—and finally show us the first fruits of our experiment. From this fruit we shall raise a new generation of seedlings which will reveal to us beyond peradventure a varied assortment of ancestral traits that the parental forms of our first hybridi- zation did not show. And from among: these diversified forms we shall be able, by a long series of selections and new combinations, to make our way toward the attainment of our original idea. The precise steps and the varying details through which this may be attained will be dis- cussed in other chapters. Here we are concerned only with the general outline, and, this having been presented, we may leave our cherry in this interesting stage of partial construction. To be sure we have not apparently advanced very far toward our ideal in these two gener- ations; but in this our case is only comparable, after all, to that of the architect who, when he has planned a building that shall ultimately tower toward the skies, must be content to see the workmen first begin digging in the opposite 204 LUTHER BURBANK direction, to lay foundations far beneath e earth's surface. Voie This matter of the very doubtful seslt olla. firet stages of » hybeidising sap ==aeae } pretty sure to hecome discouraged at the outset and to proceed no further. Many an experimenter has given up a quest q crossed the offspring seemed inferior as to the : desired quality to either of the parents. But the © experienced plant breeder knows that this is very _ often to be expected and that he should not be in the least discouraged by this result. It is gener- ally necessary to go on to the next generation be- __ fore we can Bope to Higuower Ge ae of the experiment. 4 The simple fact is that, where varieties or 4 species of plants that differ markedly as to cer- tain qualities are combined, the offspring very — frequently seem to present what has been spoken — of as a mosaic of characters rather than a blending. It may and very commonly does manifest, as regards any given quality, the influ- ence of one parent seemingly $0 1: Sam of the other. A familiar illustration of the same rule may be observed when a person having black eyes PLANNING A NEW PLANT 205 marries one having blue eyes. It is obvious that no individual child of this union can have both black eyes and blue eyes. In point of fact, it is a matter of common observation that the offspring in such a case will have dark eyes. But it has also been observed that the blue eyes of one of the parents may reappear in the second generation. The tendency to blue eyes was entirely sub- ordinated or submerged in one generation, yet it was by no means eliminated, as its reappearance in the next generation clearly proves. Similar instances without number may be studied from our plant experiments; for ex- ample, the case of the white blackberry. If flowers of this kind are fructified with pollen from flowers of a blackberry of the usual color, the hybrid progeny of the first generation will all bear black fruit. The quality of blackness has proved prepotent or dominant, and the opposed quality of white- ness has been totally subordinated so far as this generation is concerned. But if these black hybrid blackberries are cross-fertilized, from the seed thus produced there will spring a generation of brambles, some members of which will in due season produce CORN TEOSINTE HYBRIDS SEVENTEEN FEET HIGH Corn was originally a subtropical plant, and the primitive teosinte is a se plant of rather tall growth. By hybrid- ization and selection giant varietice have developed here which grow with tropical lu«uriance, reaching a height of seventeen feet. Superior for stock feed, but having small, inferior ears, — a ‘ PLANNING A NEW PLANT 207 white fruit precisely like that of the maternal ancestor. Such, it will be recalled, was indeed the experience in the development of the new race of white blackberries. To instill good qualities of fruit into the inferior original berry, it was necessary to cross with the large and well-flavored Lawton black- berry. The immediate result was seemingly to oblit- erate the white-fruiting tendency altogether. But a wide experience of similar instances led me to continue the experiment, which for the moment seemed to be carrying me away from the ideal of a white blackberry; and the principle of reversion came to my aid in the next gener- ation and gave, as will be recalled, a berry that combined the light color of one of its grandparents with the size and flavor of the other. As already suggested, it aids the memory, and helps to give tangibility to the facts, to recall the Mendelian phrase which speaks of blackness versus whiteness in such a case as constituting @ pair of unit characters; naming blackness as the dominant and whiteness as the recessive feature; and which gives assurance that a fruit which shows the recessive character of whiteness 28 LUTHER BURBANK in the second generation will thereafter breed true, thus affording us evidence of definite progress toward the ideal of our experiment. Ar rrom Unrirr CHARACTERS — As the principles that govern these cases are of very wide application, it follows that there is very great advantage from the standpoint of the plant developer, in the discovery of pairs of unit characters and the demonstration of their rela- tion toward each other as regards dominance and recessiveness. An interesting illustration of this is afforded by the experiments made by Professor R. F. Biffin, of Cambridge University, in the suc- cessful attempt to develop a new race of wheat. Professor Biffin through a series of ale 3 ments showed that when beardless ears of wheat are crossed with bearded ones, the beardless condition proves dominant, so that all the off- spring are smooth-eared; but that the recessive quality of bearded grain reappears in the second generation. The same thing held true for various other pairs of unit characters, such as red chaff versus _ white chaff, red grain versus white grain, hollow stem versus solid stem, and the like. 4 PLANNING A NEW PLANT 209 Professor Biffin was able to make an imme- diate practical application of his experiments through which he developed a new race of wheat that is proving of great economic importance. It appears that the best races of British wheat have been peculiarly susceptible to the fungous pest known as rust. There-are, however, certain races of wheat that are immune to the pest; but unfortunately these produce a very poor quality of grain. Professor Biffin found that susceptibility and immunity to rust constitute a pair of unit char- acters, in which susceptibility is prepotent or dominant. When he crossed the susceptible grain with the immune one, he therefore produced an entire generation of susceptible grain. His experiment had seemingly gone back- ward, quite as in the case of my first generation of white blackberries. But in the ensuing generation the recessive character of immunity reasserted itself; and, combined with this desired character, in a certain proportion of the progeny, there appeared the other desired quality of a good variety of grain of fine resisting qualities. So by the application of this principle of the segregation and recombination of unit charac- CORN SELF-POLLINATED AND CROSSED WITH TEOSINTE — The upper ear is an ordinary ear a | sweet corn, presenting no marked pecu- liarities. The lower ear was developed _ on the same stalk by pollenizing the type of corn called teosinte, which is — illustrated on earlier pages of the present volume. The influence of the pollen parent is clearly shown in the es modified form of the kernels. With — most plants the pollen does not directly affect the fruit, but corn is a notable — exception in this regard. a: PLANNING A NEW PLANT 211 ters Professor Biffin produced a new race of wheat in two or three generations, and this new race of wheat breeds true. We shall see this principle illustrated over and over in connection with the long series of my plant experiments. In case of the wheat, as in that of the white blackberry, the process was relatively simple because we were dealing only with two pairs of unit characters. Moreover, the case of wheat is further simplified by the fact that this plant is self-fertilized and under conditions of cultiva- tion has become a very fixed race, little subject to variation. When we deal with races of fruits that tend to vary almost indefinitely, and when further we are concerned with ten or a dozen unit charac- ters, the matter becomes vastly more involved, as we have previously seen illustrated. But the amateur will do well to begin his ex- periments with simple cases, dealing with only a single quality, say a particular color of flower, that he may thus learn to distinguish the prin- ciples here enunciated. In due course he may go on to apply these principles to more complicated experiments in plant combinations. But unless he learns at the outset that certain characters that are submerged in the first hybrid generation PLANT AFFINITIES CHOOSING THE LINEs oF LEAST RESISTANCE * HY do not plants cross in a state of nature?” a friend asked me. “You seem to get most of your new varieties by crossing old ones. Why does not nature take a leaf from your notebook and produce new species in the same way?” And I was able to inform this inquiring friend, much to his surprise, that the method he sug- gested was one that nature had practiced from the beginning, and is constantly practicing all about us. We were standing near the gateway of the Sebastopol place. “Just over by the roadside,” I said, “you may see for yourself precisely such an experiment in plant combination as I have made in the case of thousands of plants. Do you see those tarweeds? Doubtless you are familiar with them. 213 214 LUTHER BURBANK | : “Qne of them bas large showy fowans, Ge 4 other small and inconspicuous ones. The botanist calls the large-flowered species Madia elegans, and the other M. sativa, The two species do not look much alike, and some botanists ¢7Gn aiaaan them in different genera. “If you look at ell cloeely you will sala there is a third form of plant, bearing some re- semblance to each of them, growing among the __ others, and that this is a natural hybrid between 4 the two. “If you examine this hybrid, you will find that its branches are less spreading than those of its large-flowered parent, although not upright like those of the other parent; and that the stem is __ stouter than that of either parent. As to foliage, the hybrid plants have larger and thicker leaves — than those of the large-flowered tarweed, more ; closely resembling the other species in this re-— spect, but the ray flowers are intermediate in size and shape as well as color, the reddish-brown that __ characterizes the flower of the more parent being reduced in the hybeid' 8 Sra in the top of the tube. 4 “So here you are probably witnessing the crea- tion of a new species in nature. You, of course, 4 are an evolutionist and therefore are aware that all species of plants as well as animals have been a Sah a a a a ae PLANT AFFINITIES 215 - evolved in past ages by a development from earlier forms, but you very probably supposed that this creative process has now come to a standstill. Let me assure you, then, that this process is going on to-day very actively, in all probability quite as actively as at any time in the past. “Species of plants in a state of nature are constantly crossing and new species are being developed under our eyes. “There is nothing anomalous about the case of the tarweeds, although they afford a very interesting illustration of the development of which I speak. The same thing may be ob- served in the case of certain genera of the mint family. Here in some cases the hybrids thrive almost to the entire exclusion of the parent species. In other cases they gradually dis- appear, being too unstable to establish them- selves by seed. “Everything, of course, depends upon the qualities of the hybrid. If it is well adapted to the environment it survives. If better adapted than its parents, it probably displaces them alto- gether. But, on the other hand, if the hybrid is less well adapted than the parent forms to make its way in the world, it is of course weeded out by natural selection.” 216 LUTHER BURBANK In response to « farther quesy. § an for my friend, among plants that often cross in a state of nature, the various species of the genus Rubus, including the blackberry, raspberry; in the tribe of wild roses and crab apples; the California lilac, the various members of the oak tribe, the willow, the strawberry and the huckle- tactile extent Sa Indeed, is my firm conviction that erosing : between natural species is a pheneenee i almost universal occurrence. No other equally plausible explensiue all : been given of the appearance of what may seem to be spontaneous varieties or forms that furnish the material for the operation of natural selection, and are thus among the bases of organic evolution. i It is true that such a suggestion aa ae have seemed heretical not very long ago; but vast numbers of experiments in the combination of different species, and even representatives of different genera, in my orchards and gardens _ have afforded a mass of evidence that no one can ignore. So to-day it is coming to be recog- nized quite generally that the combination of wild species is one of nature’s conventional — methods of producing variability, and, asit were, PLANT AFFINITIES 217 testing out the environment by supplying new forms that come in competition with the ones already developed. Limits oF HyBripizIne But why then, you will perhaps ask, does not the production of new forms between natural species take place so universally as to disturb the entire scheme of organic nature. In point of fact, the zodlogist and the botanist are able to describe vast numbers of species, each of which has certain fairly well-defined characteristics and differs in certain definite regards from other forms. It is true that the more closely the matter is studied the more commonly varieties are found that manifest characteristics intermediate between those of the suipposedly fixed species. But even when these are taken into consideration, it still remains true that the word “species,” as applied to a vast number of familiar forms of vegetable and animal life, has a pretty definite and tan- gible meaning. How is this possible, if the interbreeding of species is a universal phenomenon? The answer is found in the facts (1) that the hybrid forms produced, when species in nature are crossed, for the most part quickly disappear SOME STEMS OF BLACK- BERRY-RASPBERRY HYBRIDS The rose, the tlethnee the ae and sixty-two other plants, dissimilar — in appearance, are ail members of the same family, and often give evidence — of the possession of common family traits. | : wleene + ¥e . (Mens Sevag na Nae abe y opus ata PLANT AFFINITIES 219 because they are not an improvement, from the standpoint of adaptation to their environment, on the parent forms; and (2) that limits are im- posed by the relative lack of affinity of one species for another. As to the first point, it must be recalled that each existing species has been produced only after long generations of struggling against ad- verse conditions. Constantly there is a tendency to variation within certain limits even in the case of the most fixed species. Such variations con- stitute tests of the fitness of the species to live in the environment in which it finds itself. Favorable variations are preserved by natural selection, simply because they have the capacity to outgrow the original form, or outlast it in times of drought or other hardship. And so every existing wild species proves by the very fact of its existence that it has a large measure of adaptability to the existing environment. It is always improbable, then, in the nature of the case, that any new intermediate form, such as would arise from the combination of two al- lied species, will be better adapted to survive than the parent form. Such cases do arise, else we should have no new species, but in general the Tule holds. So we may fairly count it excep- 220 LUTHER BURBANK _ i: tional if a combination between natural species survives beyond the first or second generation. — The struggle for existence is always keen, and the individual organism that lacks ever so little of equaling its fellows in vitality and responsive- ness to its environment must inevitably perish. Nevertheless, the experiment of producing new forms through the combination of old ones is perpetually being made, and must continue to be made, if existing forms are to remain plastic, ready to take advantage of the changed condi- tions of environment; that is to say, ready to evolve in future as they have evolved in the past. But there are limits beyond which this per- petual experimentation with new nascent species could not advantageously be successfully car- ried, and so nature puts a sharp limitation upon the extent to which the experiment may be undertaken. AFFINITY FouNbDED on CoUSINSHIP And this is done by the simple procedure of making it increasingly difficult for species to interbreed in proportion as the species become q divergent in character. 5 Tarweeds, for example, may interbreed among themselves, and various species of mint may q similarly interbreed, but no species of tarweed PLANT AFFINITIES 221 would combine with a species of mint. One member of the rose family may cross with an- other—blackberry with raspberry, let us say, or quince with apple; and in the same way dif- ferent species of oak may interbreed; but the combination of apple or blackberry with any species of oak is unthinkable. Similarly, I have been able to cross peach with almond, and almond with plum, and plum with apricot; also apple with quince, and quince with pear. Stone fruit with stone fruit, and seed fruit with seed fruit—but not seed fruit with stone fruit. In a word, the possibility of cross-fertilization between species is conditioned on a certain close- ness of relationship, which we speak of as affinity. This is a matter of actual genetic relationship. All members of the rose family, for example, have branched from the primal ancestral stem at a period much more recent than that at which the common ancestor of the present-day apple and rose and blackberry branched from the primal stock of, let us say, the oaks. In the broadest view, there is a cousinship between all species of plants; just as there is relationship between all the twigs of an actual tree. But the species of an existing genus may be likened to twigs on a single branch; other 222 + #LUTHER BURBANK = genera representing different branches which | may diverge in opposite directions, and only " come together at the trunk. : Then, too, there is a time Gemma Men Species that are closely similar in character and appearance are those that have branched from the ancestral stem in relatively recent epochs; species more distinct trace their cousinship through remoter lines; and forms so widely diverse as to be placed in different orders have been separated for still longer periods. And we must suppose that in each generation the new forms have taken on a modicum of new traits, and have tended to fix the divergence of earlier traits: through whith they: sttained sia aa ference. Tn ‘dise coures, then; it:couant Aan ee given form has branched so widely from its cousins that the harmony of purpose, so to speak, once obtained between the obtains. The racial memory as to their common ; ancestry has become blurred, if the phrase be — permitted, and each species has become so fixed — in its own manner of life that no compromise between them would be possible. 4 And so we find that it becomes increasingly A difficult to cross species that are obviously widely PLANT AFFINITIES 223 divergent in form of stem and foliage and fiower, and that in a vast number of instances any attempt to combine these forms is altogether futile. It must be understood, however, that it is by no means always possible to predicate, from observation of a given pair of more or less distantly related species, whether or not the two would be mutually sterile. Sometimes the ex- periment results in a surprise, and we are able to produce offspring when the possibility of such a cross seemed altogether improbable. Such was the case, it will be recalled, with my experiments in hybridizing the dewberry with the pollen of the apple, pear, rose, and moun- tain ash. Such was the case also with the cross which resulted in producing the sunberry, and with that which developed the plumcot. In each of these cases the pistil of one plant accepted the pollen of the other, as it were, un- willingly. But persistent effort effected the desired result, and in the three instances last mentioned fertile offspring were produced. Pos- sibly these might not have survived in the state of nature, but under the conditions of intelligent selection they provided the foundation for the development of what may be considered new species. 224 LUTHER BURBANK ee PLant ANTAGONISMS The characteristics that make i Mussa cross two species that have varied beyond certain limits are sometimes physical. Thus it may chance that the two species have _ developed the habit of blooming at different times. If the flowers of a given species are alto- gether out of bloom before the flowers of another species open, it is obvious that, in a state of — nature, a cross between these species will not occur, however close their affinity. Similarly there are two closely related species of evening primrose that do not cross under natural condi- tions because the flower of one opens only for a brief period at midday and that of the other only during the night and early morning. Again it occasionally happens that the physi- cal structure of the style which carries the pollen tube to the ovules is such as to prevent the carrying out of this essential process. In the case of a large pollen grain and an exceptionally slender style, it is possible that the fructifying substance of the pollen is debarred from finding its way to the ovule. Such cases are probably exceptional, how- ever, and the usual barrier between species is _ not perhaps so often physical as chemical. That — PLANT AFFINITIES 225 is to say, the antagonism is inherent in the plants themselves. Allied species are of such chemical constitu- tion that the protoplasm from one combines readily with protoplasm from the other. In the case of more widely divergent species it may come to pass that the juices of one plant are actually poisonous to another. In such a case it is futile for the pollen grain and pistil to meet, because no fertilizing influence will be transmitted. Even if the degree of chemical antagonism developed has not reached a stage that makes fertilization wholly impossible, it may be suf- ficient to prevent the development of a thrifty offspring. Or, as is quite usual, it may result in the sterility of the hybrid progeny, and thus put a barrier upon further advance along that line. If proof were needed that such a chemical antagonism prevents the cross-fertilization of species separated too widely, further evidence may be found in the negative results that attend the attempt to graft a branch of one of these species upon the stock of the other. Generally speaking, it will be found that species that cannot be cross-fertilized also can- not be cross-grafted. Vol. 2—Bur. H In exceptional case itis pole SAI | graft where efforts at crossing have proved — futile. Such was the case, for example, with my grafted tomato and potato vine. But, in general, the plant that refuses to mate with another plant refuses also to accept its stem as a ope: organism when grafted or budded. 3 fs However carefully the grafting snpaieaa qe may be performed in such a case, the uncon- geniality between stock and cion is soon made — manifest. The surfaces do not unite; or if union takes place there is but slight tendency to grow; or the ston. dase not thelve, a " blighted. There are all gradations—from actual poison- | ing in which there is no tendency whatever to — unite, to a partial or even temporarily complete — union, followed by separation even after years of growth—according to the degree of antagonism. _ These chemical and mechanical antagonisms between the tissues of the plants themselves — afford the surest evidence of the long period of — time during which the two species have lived un- der more or less divergent conditions, and have — been occupied, each in its own way, in the devel- — opment of new characteristics. Yet that such — intimate differences of constitution should obtain between species that show many outward points — PLANT AFFINITIES 227 of resemblance must always be matter for sur- prise to the plant lover whose attention is called to it for the first time. That this intimate record of grades of cousin- ship should be permanently fixed in the proto- plasm of the plant itself is one of the most mystifying and thought-compelling of biological revelations. If anyone were to doubt that the intimate chemical structure of plant protoplasm and plant juices may thus be depended on to reveal genetic relationships, and to mark nice shades of distine- tion between allied forms, evidence from a quite alien field might be cited that would set the matter at rest. EVIDENCE FROM THE ANIMAL WORLD The evidence in question is furnished by an extraordinary series of blood tests through which Dr. G. H. F. Nuttall, the American Professor of Biology at Cambridge University, has traced the intimate relationship of large numbers of animals of different orders. By inoculating rabbits with the blood of dif- ferent species of birds, reptiles, and mammals, Dr. Nuttall was able to develop an extraordi- nary serum with which the intimate constitution of the blood of other species of animals could be 228 LUTHER BURBANK — tested. He thus demonstrated, for example, that lizards and serpents are more closely related than turtles and crocodiles, but that all these reptiles are nearer to one another than they are to birds, and nearer to birds than to mammals. He showed that the dog carries in every drop of its blood chemical proof of closer relationship with wolves, and foxes, and jackals of every species than with any member whatever of the cat family. Similarly, all cats—tigers, lions, leopards, along with the domestic tabby—give proof, in the chemical constitution of their blood, of a common origin. And, bringing the com- parison still nearer home, the blood of man is more like that of the chimpanzee, the gorilla, and the orang, than it is like that of any other crea- tures; and the monkey tribes of the Old World are more manlike in the constitution of their blood than are the monkeys of the New World. | Dr. Nuttall’s experiments comprised sixteen thousand individual tests, with a total of at — least 586 species of mammals, birds, reptiles, batrachians, fishes, and crustaceans, coming from all parts of the globe. The biological implica- tions of his experiments have been commented upon as follows: “Doubtless some hundreds of thousands of years have elapsed since the direct ancestors of 4 5 4 PLANT AFFINITIES 229 men branched from a common stem with the direct ancestors of the gorilla. There has been no blending of blood in the intervening centuries. Cats have been cats and dogs dogs from geologi- cal epochs so remote that we hesitate to guess their span in terms of years. So the intimate chemical qualities that denote man or ape or cat or dog, each in contradistinction to all the others, must have been transmitted unmodified through countless thousands of generations. “It taxes credulity to believe that such intan- gible properties could be transmitted unmodified through the blood streams of such myriads of individuals; but the evidence of the test tubes proves that these are the facts. “What makes the marvel greater is the fact that the bodies of the animals have meantime been so modified as to develop utterly divergent species—for example, the lion, the tiger, the puma, the leopard, and the house cat; different types of dogs, wolves, foxes, and their allies. But in each case some intangible quality of the blood remains unchanged to prove the common origin. Blood is indeed thicker than water.” The bearing of these extraordinary experi- ments upon the case in hand will be obvious. If animals carry in their veins generation after generation, through untold thousands of years, A SHIRLEY POPPY—SHOWING _ REPRODUCTIVE ORGANS — oo The petale of a flower are designed — to attract insects, The essential or, che ar are the pollen-bearing stamens and the mee 2 pistil inclosing the ovule at the conten) | large ane of stamens of the poppy, yee each with a terminal anther, bearing pollen, growing in a circle about the pistil with its curiously rounded end, called a stigma, designed to receive the - ) pollen. The office of the insect is to transfer pollen from the stamens of one flower to the pistil of another. 7 2 amt pe 3 ‘ . 4 ny rg ee : ‘i E rib Sng S Mey Sekt eR Lae Ne Sh OOS aR pee eS RN eS a ee te ne PLANT AFFINITIES 231 these intimate chemical conditions, then the same thing may well be supposed to be true of plants. And so the affinity shown between species thaf can be crossed, and the antagonism between species that refuse to cross can be explained on the basis of a fundamental intrinsic quality of the protoplasm, the foundation substance of life. This gives us a more profound and compre- hensive appreciation of the word “affinity” as applied to various species of plants than we could otherwise have. It also makes it in a measure comprehensible that the traits of remote ancestors should be carried latent in the tissues of the germ plasm, as we have seen that they are carried, for un- told generations. Tue CONTINUITY OF THE GERM PLAsM This germ plasm, which is the connecting link between one generation and another, is passed on, according to the most prevalent idea, from parent to offspring, generation after generation, subject only to such modifications as may from time to time be imposed through environing influences. The physical mechanism that underlies this _ transfer we shall have occasion to examine in _ another connection when we discuss at some 232 LUTHER BURBANK length the theories of heredity. For the moment it is enough to reflect that as the offspring in each successive generation spring from the parent, the germ plasm may be thought of as a continuous stream uniting the remotest ances- tor of any given strain with the most recent — descendant. Every tree in the orchard, for example, car- ries within its tissues a portion of protoplasmic chemical matter that has come down to it through an almost infinite series of growths and divi- sions in unbroken succession from the first tree that ever developed on the earth—or, for that matter, from a vast series of more primitive organisms that were the progenitors of the first tree. | And while this stream of primordial proto- plasm has been changed by an infinitesimal quantity in each successive era, it has retained even to the present the fundamental character- istics that it had from the outset. That such is the case seems little less than a miracle; that an almost microscopical speck of protoplasm which we term a pollen grain should contain the potentialities of thousands of tions of ancestors, and should be able to transmit them with such force that the seed growing from the ovule fertilized by that pollen grain will — g . a J PLANT AFFINITIES 233 inevitably produce, let us say, an apple tree, not a pear tree or a plum, is beyond comprehension. Yet we know it to be true. And so the plant breeder who consciously merges two different protoplasmic streams when he brings the pollen of one flower to the pistil of another, participates in what must be consid- ered the most wonderful of all experiments. He brings tokens out of an almost infinite past to blend with the divergent tokens of an- other ancestral stream no less ancient. And it is not strange if he feels a certain im- pulse of elation when reflecting that his conscious efforts have thus brought together ancestral tendencies that have long been separated and that now will appear in new combinations— stimulating such interplay of life forces as may bring into being plant forms that may be described, without violence to the use of words, as new creations. That the intimate record of cousin- ship, in all its grades, should be permanently fixed in the proto- _ plasm of every living thing, is a thought - compelling biological revelation. PRACTICAL POLLINATION A Survey oF WorkinG METHODS NCE upon a time—it may have been about the year five million B. C.—a plant imbued with nascent wisdom made a tacit compact with a fellow creature of the world at large that was fraught with strange and fateful meanings for races of beings yet unborn. The fellow creature in question was at that time probably the most highly developed citizen of the world, although in modern terminology he would be termed “merely an insect.” The com- pact the plant made with him was to the effect that one should manufacture sweet nectar and freely supply it as food; and that the other in return should carry the fructifying pollen grains from flower to flower. Doubtless no more important compact was ever entered into in the history of animate crea- tion before or since. For out of this compact grew the rivalry that stimulated development and made possible the 235 POLLEN-BEARING PUMPKIN BLOSSOM | Many plants bear pollen and ovule on separate blossoms, so that self-fer-— eae tilixation is impossible. This picture shows a pumpkin blossom with the modified and coalesced stamens at its center bearing a quantity of pollen. The insects in visiting the blossom carry the pollen on their bodies or feet and transfer it to other flowers. PRACTICAL POLLINATION 237 evolution of the whole race of plants that bear beautiful flowers and exhale sweet perfumes. But for this eventful alliance, there would never have developed in the world a conspicuously colored or a fragrant flower of any kind. And it requires no argument to show that a world without beautiful and fragrant flowers would be a world robbed of a large share of its attractions as an abiding place. But that is not all. The alliance between in- sect and flower did not merely suffice to give us things of beauty. It bespoke utility as well. It made possible the bringing together of germ plasms from plants growing far apart, thus in- suring virile and variant strains; and this de- termined in large measure the amount and direction of the evolution of the highest orders of plants. For it must be observed that, with rare excep- tions, the higher plants are precisely those that long ago entered into this cooperative scheme whereby they trusted their fate absolutely to the insects. They hazarded much—for if anything should lead to the destruction of a few insect races, entire orders of plants would have become extinct. But if they risked much, they also profited much; for the cross-pollenizing effected by the insects afforded the constant stimulus to So REP ee ee 238 LUTHER BURBANK > variation that underlies all evolution, oad enaligl _ the plants that entered into the ae eee ently to outstrip their fellows. | Wherever you find « tribe of plasts Mabaene great diversity of form, large numbers of species, and ready adaptability to improvement, you will as a rule find a tribe of so-called “entomophi- lous,” or insect-loving flowers, dependent upon — the winged messengers for the consummation/of their matings. Vest responsibilities then were implied in this | coalition of the plants and the insects; but reid results have justified the hazard. a Prants Tat Dm Nor Jors rue Union We shall presently see illustrated in detail the curious adaptations of form and color and structure to which the plants of various species were led in their rivalry to secure the good graces of the insects and hae to mle a uating their species. Every blossom of the entire orchard, every flower of the garden, and with a few exceptions all of the vegetables under cultivation furnish illustrations in point. But it should be recalled that there are large numbers of plants of a lower order that from the outset refused to enter into the coalition, and that even to this day have a ea ee ee Le PRACTICAL POLLINATION 239 declared themselves independent of the plant- insect union. Parts of this nonunion clan are the entire races of lowly mosses and lichens; a goodly number of aquatic forms that maintain the appearance and manner of their remote ancestors; and the familiar tribe of ferns; and the trees which depend mainly upon the wind. Of these, the ferns, mosses, and other forms less familiar to the amateur, have obstinately retained throughout the ages the primeval habit of propagating their kind, not with immobile pollen grains, but with the aid of self-moving germ cells. These motile germ cells, of micro- scopic size, find their way through the water— supplied in case of land plants by a film of rain or of dew—from one plant to another, and effect cross-fertilization without calling in the aid of any allies. They do not need to attract insects, and so they have not adopted the system of advertising through the development of large and showy blossoms and nectar cups to which the members of the plant-insect alliance are obliged to resort. But if the lowly plants thus maintained their independence, they have done so at a very great sacrifice. They are not more independent than they are unprogressive; and indeed they are unprogres: SEED-BEARING PUMPKIN — BLOSSOM : This blossom is the mate of the one next preceding. The stigma to receive the pollen occupies the same position — that is occupied by the pollen-bearer in — the other flower. The bulbous growth at the base of the flower is the ovary, or seed case, which, if the flower is ferti- lized, will develop into a pumpkin. PRACTICAL POLLINATION 241 sive precisely because of their independence. The method of cross-fertilization that they have adopted does indeed enable some of them to blend the strains of different individual plants; but in every instance the parents must be grow- ing in the immediate vicinity of each other. Except by the accidental’ and most unusual transfer of a plant through the agency of a passing animal, there is hardly the remotest chance of effecting cross-fertilization between individual mosses or lichens or ferns growing in widely separated regions. But we have already seen that it is precisely this blending of traits brought from parents growing under different environing conditions that is chiefly responsible for making plants vary and furnishing the materials for evolutionary progress. So it goes without saying that the plants that are restricted in the choice of possible mates to individuals growing under the same conditions to which they themselves are sub- jected, cannot expect to change rapidly and therefore do not evolve in any such ratio as plants having the other habit. And in point of fact we find that the plants that retain this primitive custom of fertilization with the aid of motile germ cells, acting quite independently of insect or wind, are plants of a . 242 low order of development, showing relatively little diversity of form and small capacity te adaptation. = a The most conapicnous’of, them wits aidaanne ; ordinary observer is familiar, namely, the ferns bear a striking resemblance in contour to plants of the remote Carboniferous Era, traces of which have been preserved in the coal beds. And there can be no doubt that this persistence of the primitive form has been largely due to the special method of fertilization which the ferns bave: retained. If it be permitted to carry perecnienhen ae stage farther, we might say that the ancestors of the ferns belonged to a conservative family, jealous of its independence, and unwilling fe enter into outside alliances. And the penalty of conservatism hem:ens so opin in. the range of heen aaa racial stasis, 2 Puants Tuat Haye Lert tHE Union It would appear, however, that there are certain races of plants that were once members of the plant-insect alliance but which are now no longer in the union, These apostates include two quite different 4 tribes of plants. PRACTICAL POLLINATION 2438 On one hand there are numerous gigantic trees that no longer depend upon insects for the fertilization of their flowers. On the other hand there are little cowering plant waifs that nestle close to the earth and which, in quite a different manner, also assert their independence. The trees that have thus revoked the treaty of alliance include such familiar forms as the pine, the oak, and the walnut. These trees, and a goodly number of their fellows, long ago declared against further co- operation with the insect, and adopted the method of producing large quantities of pollen and scattering it in the air to be carried by the wind to the pistillate flowers, which in some cases grow on neighboring branches and in other cases on quite different trees. The method is in one sense wasteful, inasmuch as it involves the production of vast quantities of pollen, only an infinitesimal portion of which will ever come in contact with a receptive pistil. And of course the production of this pollen must draw heavily on the energies of the living substance of the tree. But, on the other hand, the tree that thus depends upon the wind rather than upon the insects is under no necessity to develop large and gest the need of cross-fe ili the economy of plant life. — : PRACTICAL POLLINATION 245 conspicuously colored flowers. Nor need it pro- duce nectar to feed the insect allies, since these have been renounced. And it may very well chance that the saving of energy thus effected more than counterbalances the waste through excessive pollen production. At all events the plants that have adopted this system of pollinizing give evidence that their plan is not a bad one in the very fact of their extreme abundance. Moreover the “wind-loving” or “anemophil- ous” plants, as the botanist terms them, have not only produced a great variety of species and vast numbers of individuals, making up the bulk of our forests, but the individuals themselves are of such virility of constitution as to attain gigantic size. Indeed a moment’s consideration makes it clear that the plants that had depended on the wind rather than on insects for fertilization are quite in a class by themselves in the matter of size, inasmuch as they constitute the bulk of our temperate forest trees. This relation between size and habit of spread- ing the pollen broadcast on the winds cannot be altogether accidental. But whether the trees grew large because they had given up the alliance with the insects, or whether they gave up the alliance because were relatively neglected by the insect messen- — gers. But, on the other hand, there are insects — that haunt the highest trees, and we can hardly to obtain the services of insect messengers, races of these would have been developed that would have proved equal to the most exacting demands. What seems on the whole most probable, then, is that the trees have adopted their method be- Suase of the very wanine Of Uae ee air they obviously put themselves more in contact As a matter of fact we iow that the sath a of pine trees in particular may be carried almost _ in clouds for scores and even hundreds of miles. So there is every opportunity for the cross- — fertilization of individual trees growing in widely separated territories; and there is therefore no — restriction put upon the possibilities of progress PRACTICAL POLLINATION 247 and evolution for these large-growing plants in penalty for their renunciation of the services of insect messengers. The case of the trees, then, simply illustrates the fact that there may be more than one way to effect a given purpose, and that a change of method may be no barrier-to progress, even though the abandoned method still remains an admirable one for a vast coterie of organisms of slightly different habit. SELF-FERTILIZED PLANTS But the case of the other company of plants that have backslidden from the insect alliance is altogether different. The plants in question do not make up any great conspicuous tribe comparable to the forest trees, but are a miscellaneous company of lowly vegetables of unrelated families. Familiar ex- amples are the wheat of the fields, peas and beans in our garden, and a certain number of the more obscure species of violets. The jewel weed, the fennel, the rue, and the nettle are other somewhat less familiar yet not uncommon tribes of plants whose flowers are habitually self-fertilized. There can be no question that these plants are the descendants of tribes that were at one time 248 LUTHER B of the wheat, which might be thought a possib exception, there is the evidence of certain specit of wild wheat, growing to this day in Palestine, — which have only partially renounced allegiance — to the insects, still putting forth flowers that on — occasion may be cross-fertilised Wii Seam ay with that of the wind. Ve 5 Just why these various plants of different families have departed from the custom that has : served their fellows so well, would be interesting — matter for conjecture. eo Yet that wheat should make this change eos j doubt because it has under cultivation been — grown en masse, giving it no opportunity for individualization. The most plausible sugges- tion is that the ancestors of the plants that now have closed flowers and thus depend exclusively upon self-fertilization had fallen upon evil days — on which there was a dessa ee in the regions they inhabited. 4 The story of the starved martins, told in an q earlier chapter, furnishes a striking illustration — of the fact that insects that ordinarily are abun- — dant may in any given season fail to make their — appearance. Ue! apie oe eet 5 phot es ee a ee ee Ce on ee i A ia a PRACTICAL POLLINATION 249 And even if the insects themselves are abun- dant, the weather conditions, in a given season, may be such as to make it almost impossible for them to carry out their bargain by transferring pollen from flower to flower. Every orchardist knows that a protracted rainfall just at the time when his apple, pear or plum trees are in bloom may prevent the bees from visiting the flowers; and in such case, as is only too well known, there will be a partial, or no crop that season. With trees and other perennial plants it is not a matter of absolutely vital importance that there should be a crop of seeds produced each season. Failing progeny this year, next year or the year after will answer in the case of a plant which grows on a permanent stalk or from roots which outlast the winter. But the case of the annual plant is altogether different. Should such a plant fail for a single season to produce seed, its entire race might vanish instantly from the earth. That thought is rather startling when pre- sented thus tangibly. Yet its truth is almost axiomatic. Quite often the entire seed crop of an annual plant in a state of nature germinates or decays the ensuing PRACTICAL POLLINATION 251 season after its production. And it is absolutely incumbent on the plants that grow from this seed to produce in turn an annual crop of seed that will carry on the racial stock. So it is not strange that a plant that is thus perennially threatened with destruction should adopt exceptional measures to insure the fertili- zation of its flowers. Very often it may have happened that certain individual flowers that chanced to be self-ferti- lized were instrumental in saving the life of a species that otherwise would have been exter- minated. And as, through the operation of heredity, the offspring of these flowers would tend to reproduce the self-fertilizing habit of their parent, the surviving representatives of the species might thus come to constitute a tribe in which the habit of bearing self-fertilized flowers was the prevailing custom. And thus it is, perhaps, that the method of reproduction followed by the wheat in our fields and the peas and beans in our gardens may be accounted for. Yet the fact that certain of these self-fertilized flowers, as for example the violet, retain the custom of putting forth showy flowers even though these for the most part are seedless, shows how powerful is the hold of remoter heredity, 252 LUTHER BURBANK and how persistently the plant clings to's custoin : to which its ancestors owed their racial preserva- — tion. Moreover, it has been observed that the © i comtie teooa, made accessible to insects, _ resume the | custom of growing seeds by its conspicuous — flowers, whereas hitherto it had produced them — only in the inconspicuous bulite ee never open. Scuemes To Insure POLLINATION _ . It is curious to observe how insistent is the © inherent demand for fertilization of the flower, — god bow oven Sewers tint get See the insects may strive to provide for self-fertili- — zation in the event that their call remains un-— answered and in vain. J The common barberry (Berberis valgieid)) for — example, opens and exposes its pollen-bearers only during the bright hours of a cloudless — day. But in case an insect fails to Waa” provision is made that will insure self-ferti- — | lization; for in due course the stamens dart — forward and sprinkle their pollen over the pistil. In the case of the fennel flower of Fretted described elsewhere, which does not open at all, — the pistils bend forward when they are ripened, — PRACTICAL POLLINATION 253 and after taking the pollen from the stamens, straighten up again. With the rue, the arrangement is curiously complex and machinelike. Of the several stamens, each in turns bestows its pollen on the pistil at their common center. It has been observed that the stamens advance alternately, numbers one, three, and five in turn; numbers two, four, and six following in succession, as if the entire mechanism were actuated by clockwork. But these and sundry other ingenious mech- anisms for self-fertilization after all only evi- dence the resourcefulness of a plant in its struggle for self-preservation. It is better that a flower should be self-pollen- ized than that it should not be pollenized at all. But the process is in no wise comparable, in its value for the race, to the more usual process of cross-fertilization. The self-fertilized plant develops fixity of race. It lacks the needed stimulus of the blending of different racial strains. It will produce few varieties, thus giving little opportunity for the cperation of natural selection. _ In a word, such a plant is really marked for ultimate extinction, unless, as in the case of the wheat, man steps in to give it the refuge of artificial selection. PRACTICAL POLLINATION 255 It may well be doubted whether the existing races of cultivated wheat could perpetuate their kind, if put upon their own resources in com- petition with wild plants, for a dozen or two dozen years. The habit of self-fertilization may preserve for a certain number of generations a plant that would otherwise have been completely extermi- nated; but at best it marks a stage of degenera- tion and decline. The plant that follows it is in a sense retracing its steps down the ladder of evolution by which its ancestors have made ascent. And so it is not surprising to find that the vast majority of the useful plants of orchard and garden have kept up the traditional alliance with the insects to which they owe the multiplicity of their specific forms and the virility and adapt- ability of the individual members of their organization. THE WIsEsT OF PLANTS 3 It is flowers of the great brotherhood of insect 4 lovers, then, that chiefly claim the attention of _ the plant experimenter, because these are the _ ones that make up the chief census of orchard _ and garden. _ As a matter of course it is plants of this _ fraternity that are of interest to the amateur, because, generally speaking, it ls thane slopes put forth blossoms that please the eye. — Whoever is isiterested 10 maleuiae aun: ments in plant breeding must, then, familiarize — himself with the mechanisms by which the plant makes known its appeal to the insect and those through which the perpetuation of its kind is effected; the mechaniams, thet oe typical flower. aad ees As we come to study flowers in detail, it essential organs of the flower in separate blos- ; soms. Reference was made to this in the case — of our crossing experiment with a certain species — of dewberry, and we shall see other illustrations _ of it from time to time. 4 But the major part of the most familiar calth 4 vated plants, including all the conspicuous fruit — trees of our orchards, bear flowers each of which — contains within the same blossoms both the stam- inate and the pistillate organs. q Ordinarily it is the function of the hes to. carry pollen from one blossom to the pistil of — another. But on occasion even these flowers may _ be self-fertilized. Thus it may be said that the most important, from a human standpoint, — PRACTICAL POLLINATION 257 among the existing plants have adopted a com- promise in which cross-fertilization is the rule, yet which makes possible self-fertilization in case, under the stress of circumstances, cross- fertilization should fail to take place. Doubtless, on the whole, this was the best course of all. The plants that adopted it might be said to be the wisest of their kind. Tue TypicaL FLOwER What may be regarded as the typical or per- fect flower, then, is one that contains both pollen- bearing and pollen-receiving parts, surrounded by the conspicuous insect signal that we term the coroila; and having also a less conspicuous outer shield termed a calyx. The calyx is the original shield about the flower bud, and its function is over when the flower opens. The botanist ordinarily speaks of the calyx as _ modified leaves. He refers to the petals of the _ corolla as being also modified leaves or enlarged and beautified modifications of the calyx. He thinks of the stamens and the pistil as _ modified petals; and he justifies this estimate by showing that under cultivation it is often _ possible to transform these essential organs into petals. Vol. 2—Bur. I 258 LUTHER BURBANK _ Thus, for example, are produced such doubk flowers as the cultivated rose, dahlia, and the chrysanthemum. To the human eye, these are things of beauty but from the standpoint of plant economy they must be regarded as travesties of flowers, since they are far less able and often But it is perhaps a somewhat more :philo- sophical view of the flower to consider it as a mechanism developed about the oe . tral organ, the pistil. This, the’ female organ. of. the plea aaa in the developed form, of a basal structure, the ovary, containing the ovules or embryo seeds, and a more or less protuberant style at the end of — which is the stigma that \reselnas Aaya pollen. Considered. as ‘to. ite origin, the SaumnnEn effect a modified bud. Everyone is aware that individual buds of a plant may have the — property of being able to reproduce the entire plant. The pistil is a modified bud each em-— bryo seed of which, when fertilized, as the same potentiality. By the most wonderful maitecks of AE world, this infinitesimal structure is enabled to — epitomize all the possibilities of a future plant, of predetermined size and form and habit. — PRACTICAL POLLINATION 259 lt differs from the bud from which it is de- veloped chiefly in that it requires to be fertilized by union with a pollen cell, before it is capable of taking on development; and in the further very essential fact that when mature it may be cast off from its original moorings and carried to any distance, thus in a way making amends for the limitations put upon vegetables by their inca- pacity for locomotion. The stamens that normally grow in a circle about the central pistil develop at their ends anthers that produce, usually in relatively large quantities, pollen grains of exceedingly minute size. And each pollen grain contains, somewhat as does each ovule, all the hereditary potentiali- ties of the entire plant. The pollen grain cannot, indeed, be made to develop into a plant; but its union with the ovule is essential to the develop- ment of that organism, and it is certain that the pollen grain, despite its infinitesimal size, brings to the union factors that represent its parent plant effectively and in full measure. It would be unbelievable, if we did not know it to be true, that a fleck of matter of scarcely more than microscopic size should contain the potentialities of a mammoth tree, and should predetermine the details of structure of a future tree even to its remotest leaf and to the finest t YW Aa Ske. y PP p 4 CROSS SECTION OF A CACTUS BLOSSOM This is what is called a perfect — flower—that is to say, one that has both stamens and pistil, The stamens are : grouped in a circle about the pistilas in the case of the poppy; this being the:sine shows the seed case or ovary at the i Ws i cent ceive the nucleus of a pollen grain orit will not develop. Where the stamens _ are thus clustered about the pistil, cross- fertilization is usually prevented by the maturing of the two sets of wees’ f at different periods. ca ee ; eee a) PRACTICAL POLLINATION 261 details of its flowers and fruit. But that the pollen grain actually has these potentialities has been demonstrated thousands of times over by the plant experimenter. Any amateur who wishes to test the matter may do so, to his complete satisfaction, by making the simplest experiment in cross-pollenizing and watching the growth of the hybrid seedlings his work brings forth. The pollen grain effects union with the ovule by sending out a threadlike filament of proto- plasm, like a tiny root, which penetrates the stigmatic surface, passes down along through the style, and carries the nucleus of the pollen grain to the nucleus of an ovule. When the two nuclei come in contact, fertilization has been accomplished. . When pistil and the stamens have been con- sidered, we are through with the really essential mechanisms of the flower. From the human standpoint, of course, chief interest centers in the corolla with its widespread- ing petals of varied colors. To the plant itself this structure is in a sense essential, inasmuch as it supplies the visible signal that attracts the attention of the insect. But beyond this it has no share in the process of fecundation. We shall have occasion to consider the form and structure 202 LUTHER BURBANK of this showy portion of the flower in a multitude of individual cases, and to observe how it may be modified by process of selection, but from the present standpoint it does not call for further consideration, From the standpoint of the pollenizer, the | stamens with their pollen-bearing anthers and the receptive pistil—with or without a stigma at its tip, but always having one or more ovules in the egg case at its base—are the organs that claim exclusive attention. HAND-POLLENIZING ote The essence of pollenizing is merely the transfer of pollen from the stamen of one flower to the stigmatic surface at the end or rarely at the side of the pistil of another. 3 This is the work that is ordinarily accom- plished by the insect. It is all that the plant experimenter accomplishes when he wishes to effect the crossing of different plants of the same species or the wider crossing, commonly called hybridizing, of different species. There is nothing occult in the practice of the bee or in the imitation of his work as practiced by the hand of the pollenizer. What is accomplished in each case is the purely mechanical transfer of a certain number PRACTICAL POLLINATION 263 of minute pollen grains from one place to an- other. Beyond that, everything depends on the vital activities of the plant tissues themselves. We shall have occasion in another chapter to deal somewhat at length with specific methods that are necessary to effect cross-pollenizing in the case of sundry types of flowers that have de- veloped blossoms curiously modified as to form or details of structure. But the general proc- esses of hand-pollenizing, as they apply to the chief flowers of the orchard and garden, may be stated in a few words. The essential thing is to secure a certain quantity of pollen, usually by shaking it from the flower on a watch crystal or other small re- ceptacle, and to transfer this pollen to the recep- tive pistil of another flower either with the finger tip— which furnishes in general the most useful piece of apparatus—or with a camel’s-hair brush. It is desirable to cover the receptive portion (stigma) of the pistil fully with pollen, partly to insure complete fertilization, and partly to prevent the vitiation of the experiment through possible subsequent deposits of pollen from another source. If the flower to be fertilized has stamens of its own, these should be removed before they RASPBERRY BUSH AFTER ) POLLINATION Here small paper bags have been — tied loosely over the flowers that have — been cross-fertilized. It is not usually necessary to resort to this expedient, __ for if the stigma of a flower is entirely covered with pollen, there ia Uttle~ make assurance doubly sure, pm 4 larly by the amateur who operates on a small scale. se. Sawa © Tie gee SS a ie A PRACTICAL POLLINATION 265 are fully ripe—which is often a few hours or a day before the foreign pollen should be applied. This removal of the stamens may usually be done with a pair of small pincers. In case of flowers that have short pistils — the cherry, apple, and other orchard fruits being good examples—the unopened flower bud may be cut around at about the middle with a thin-bladed knife, the anthers being thus excised at a single stroke. With other flowers the mechanical details vary, of course; but the process is sometimes quite complicated and calls for skill and common sense. So-called composite flowers, however, re- quire special treatment. The daisy and the sunflower are familiar examples. Here the true flowers are very small and grouped in masses. Individual treatment is usually out of the question. The best method is to wash away the pollen with a carefully directed stream of water from a garden hose, or by spurting water from the mouth; after which the head of the pollenizing flower is rubbed against the one selected, thus effecting fertilization en masse. In exceptional cases it may be desirable also to cover the fertilized flower with a paper bag to prevent the visit of insects; but in practicing pollination on a large scale this may usually be 266 LUTHER BURBANK omitted by those who have experience enough to recognize the hybrids from the others. If the stigma has been satisfactorily covered Wat "pollsa te will peecmnt 9 Se Soe for the reception of other pollen grains. — The rule is simply this: Seek nature's plan and follow it. In other words; take's leson freas-the band and pollenize the flowers somewhat as they do. Bear in mind the essentials of the process, which are the same for every flower. Study the mechanism of each new flower and adapt your precise method to the needs of the individual case. It does not matter just how the pollen reaches the stigma, provided it does reach it. — A very short course of practice will give you the knack of cross-pollenizing, and enable you to enter on a course of experiments that will lead to surprising, fascinating, and perhaps far-reaching ee ens wick ay re ee world-wide significance. The ferns belong to a conservative family; and the penalty of conser- vatism, whether in plants or in human beings, has always been racial stasis. QUANTITY PRODUCTION On SEEDLINGS AND THEIR CARE HE word “evolution” chances to have nine letters. Suppose that these letters were penciled on nine blocks of wood that are otherwise identical, and these little blocks were put in a bag and mixed together. Suppose then that you were asked to put your hand in the bag and bring forth one block after another, placing them in sequence as you brought them from the bag. What probability is there, do you think, that your blindfold selection of the blocks would result in bringing them out in such sequence as to spell the word “evolution”? A mathematician could doubtless figure out the exact probabilities, but you need not be a mathematician to realize that the chances are — almost infinitely against you. Now, am I not right in saying that the plant developer who expects to find a considerable number—let us say nine—of particular qualities 267 But it is obvious thet your chance luau drawing of the blocks would increase in propor- tion as the number of attempts yon Scaaaaaaa to make increases. So would the plant experimenter’s chinaiek 4 finding several desired qualities of his fruit or flower combined in just the right proportion 7 of seedlings among which he can select. Yet I suppose the mathematician would assure us that the number of attempts you must make with the blocks before you could hope, according _ to the theory of chances, to bring out all the — letters in just the right sequence would be so — large as to tax your patience beyond endurance ~ and I can testify that the same thing holds true — with regard to the experiment of the plant de- — veloper. Though he had thousands of seedlings — among which to choose he is not likely to find — any one in a given fraternity that fully moult q his ideal. ™ QUANTITY PRODUCTION 269 _ But if in making your experiment of choosing the lettered blocks you were permitted to retain the blocks bearing the letter “E” when you chanced to draw it first; and if then you were permitted to retain the letter “V” when that was first drawn from the remaining group of eight blocks; and so in sequence with “O” and “L” and the rest—it is obvious that each new test would find you with a smaller number of letters from which to select, and hence with an increas- ing probability of successful selection. When, finally, there remained only two letters in the bag, your chance of securing the right one in the first draw would obviously be an even one. And when only the final “N” remains, you could make no mistake—your selection of the right letter then becomes a certainty. This illustration is made because I think it has peculiar application to the case of the plant developer. His method is not unlike the method of selection just suggested. As the result of his first hybridizations, he does not dare to hope that he will secure the exact combination of qualities he would like to see aggregated in his ideal fruit or flower. But by having a large number of seedlings from which to select he may reasonably hope to secure one that will present some one at least of the desired qualities in superlative degree. “FLAT” WITH LAYER OF GRAVEL ‘A layer of gravel is put at the bottom of the germinating bow to facilitate drainage and aeration, both of which are very essential to the proper growth of the plant roots. This is a detail of — special importance. ae QUANTITY PRODUCTION 271 This selected seedling he may nurture and use as part of his equipment for further experiment just as you retained the letter “E” as marking the beginning of your success in spelling the word “evolution.” And as the plant developer continues his ex- periment with successive crossings and succes- sive selections, he will be able in later generations to find individual seedlings that combine succes- sively more and more of the qualities he is seek- ing. When, finally, he reaches the stage where the parent forms have between them all the de- sired qualities in superlative degree, he is some- what in the position that you were in when only two of your lettered blocks remained in the bag. There is at least an even chance that he will find among his seedlings of the next generation one that will approximate his ideal, even though the number from which he selects is far smaller than the earlier groups. Thus by advancing step by step and using the ground gained as a new starting point the experimenter attains his end with comparative celerity, even though there would have been scarcely more chance of attaining that end with a single experiment than you would have had of spelling out the word “evolution” at a single series. 272 LUTHER BURBANK > But’ it. must be fairly’ reneaanee ae probability of success is enhanced if at any of’ the earlier stages of the work you have opportunity to select the best plant among a large group instead of being restricted in choice to a few individuals; just as the chance of securing the block you seek in each successive crewing Dncronang wah: Gee are permitted. And, in point of fact; this; ox:ssmiinienl ane this, is the actual method in which the experi- ments of the plant developer are carried out, whenever he is attempting to construct a new fruit or flower or vegetable having a number of specified or clearly imagined qualities. In such a case, the wise experimenter does not hope to secure ideal results by a single combination; he seeks to group desired qualities of his flower or fruit together through successive crossings and selections. Keeping one supreme quality in mind and perhaps two or three others in the immedi- ate background, he makes sure of first one and then another of these qualities, adding to them by successive crossings and selections, and thus, although advancing, as it were by indirection, and at first seeming to advance but slowly, he may ultimately work with increasing certainty — and approach his goal somewhat rapidly. i QUANTITY PRODUCTION 273 For example, our first cross, say in the case of a prune, may be made between two varieties that both show a fair quality of fruit. Careful attention to the result will guide us in the matter of the next experimental crossing. We soon discover which qualities are prepotent, and which tend to remain latent, and by selecting only individuals that show a tendency to vary in the desired direction, we introduce an element of direction into the experiment. I am accustomed to speak of this as “the mo- mentum of variation.” We do not always know why a certain plant tends to vary in a given di- rection, but we may observe the fact, and the wise experimenter is always on the lookout for this tendency and ready to avail himself of the advantages it offers. Technical workers some- times give the name “orthogenesis” to this tend- ency to vary in a certain direction, mentioned above as the plant’s “momentum.” Whatever aid we may gain in this way, however, the manner of our advance is often devious. In fact, it is very likely to be somewhat com- parable to the progress of a sailing ship which tacks this way and that, and which at times may . seem to be progressing in the wrong direction, yet which in the end forges ahead. “FLAT” PARTLY FILLED WITH PREPARED COMPOST | The “flat” is partly filled, on top — of the layer of gravel, with specially prepared soil, which is then tamped i , making a flat sur- — face on which the seeds are sown. The seeds are covered to about twice their — diameter with light, sifted mem QUANTITY PRODUCTION 275 Take by way of illustration the case of our stoneless plum. We discover soon that the stone seed is prepotent or dominant, and stonelessness latent or recessive. So we must be prepared to see the progeny of our first generation of hybrids all produce common stony fruit. But a knowl- edge of the tendency of latent or recessive characters to reappear in successive generations comes to our aid, and we go on with the experi- ment with full confidence, even though for the moment we seem to be going backward rather than forward. In due course the second generation of plums appears with a number of stoneless specimens, the latent character having come to the surface. But these lack many of the good qualities that our perfected fruit must have, and in order to breed these qualities into the stock we must make @ new cross; and this will involve the breeding in again of the tendency to bear stone fruit. So in three generations we shall find ourselves, as regards the essential quality of the stony seed, somewhat further back than we were in the be- ginning. But, on the other hand, our third generation fruit, even though it has a stony seed, has quali- . ties of flesh that its stoneless ancestor altogether lacked; and in the fourth generation we shall be 276 LUTHER BURBANK | prepared to find individual seedlings that bea stoneless fruit of greatly improved quality. — In each succensive. qeneration;s4iaus ata paling with better mater gees grouped, if you will. Whuyxrse Acarxst Opps But, in a, cenes, we-are-rucmias eee the trend of heredity, because the vastly greater proportion of the ancestors of our plum were — bearers of stoned fruits. And so we must con- — tinue reshuffling and dealing over, as it were, and watching results. We may lose in one genera- tion what we gained in the generation before as regards the matter of stonelessness; even while on the whole advancing toward the productionef q a fruit of desired quality. j But just in proportion as our ideal calls for 3 the combination of numerous good qualities,does the attainment of that ideal become difficult. Even when, at let us say the fifth or sixth — generation, we interbreed individuals that have — the desired quality of stonelessness, we shall not — at once secure what is desired; because our ~ seedlings combine so many ancestral traits that — they will not breed true. Even though they are — all stoneless there will be a great variation as — to other qualities, and it is only by dealing with — Nr + ed OSE Pel ee SSA ee ee & Se = et as a TN ee a RTE, ley ae a acd QUANTITY PRODUCTION 277 large numbers of seedlings that we can hope to find one or two that will show the desired com- bination of traits in high degree. _ And the lesson which should be preeminently inculeated is this: You must make many experi- ments at plant breeding before you can hope to secure the final combination—the sequence of qualities—that you desire. Tue Logic oF QUANTITY PRODUCTION Now note the application: Each individual seedling of a hybrid strain represents a unique combination of ancestral traits, and constitutes in itself a new and unique experiment—equivalent to an independent deal of the cards. So the prob- ability of securing what we seek will be somewhat proportionate to the number of seedlings. This is particularly true in the case of such variable plants as the fruit trees of our orchards. The case is far simpler when we are dealing with plants that vary little in their qualities, or where we are breeding with only a single pair or two pairs of unit qualities in mind—say “hardness” of kernel and immunity to rust, as in Professor Biffin’s experiments with wheat; or good flavor and whiteness as in the white blackberry. But where the varied traits sought to be com- bined in a Shasta daisy are in question; or the 278 + LUTHER BURBANK — many quills ofS CoS ee the case assumes new complexities. Hence it is that my resords tell of Selle applied to about half a million seedlings of the daisy; prtheen ganda million seedlings of various plums, and the like. Hence also the constant necessity of what my neighbors speak of as ten-thousand-dollar bon- fires in my orchard, when we burn seedlings that have been inspected and found wanting. To burn 65,000 hybrid blackberries in one pile, as I once did after saving perhaps half a dozen individual plants for further testing, seems like willful ex- travagance to the casual observer, but it is an unavoidable incident in the search for parr fruits. and the growing of seedlings. In point of fact, it might be said that this is the most important part of a plant breeder’s task, so far as the — practicalities of experiment are concerned. It a is part and parcel of his daily routine. It is highly desirable, then, that the wothdies 7 experimenter should gain a clear understanding of the essentials of method of caring for seeds — and cultivating seedlings. So it is the purpose in © the succeeding pages of this chapter to give a — ea Te ATER ha Such prodigal use of materia implies a lange ] measure of experience in the handling of seeds QUANTITY PRODUCTION 279 few practical hints as to various aspects of the subject. Thus summarized, the lessons learned in the hard school of experience may enable the reader to avoid some pitfalls and to make certain experimental short cuts. Keeping Seeps Over WINTER To begin at the beginning, let us note that the preservation of seeds over winter calls for care- ful attention. All fruit seeds except those of apricots and almonds, when removed from the fruit, are at once placed in slightly moist, coarse sand or fine gravel or in sterilized sawdust. In warm climates the boxes containing the seeds are then buried on the shady side of a building or tree where they will become neither too dry nor too wet. The object is to keep the kernels as nearly as possible in their original condition. If tree seeds, especially those of the cherry, the pear, and the plum once become thoroughly dry, it is difficult, and in some cases impos- sible, to induce them to germinate. An im- portant function of the pulp of these fruits, in the original wild state, was, presumably, to keep the seeds moist until the season for germination. 280 LUTHER BURBANK | I have elsewhere called attention to the ex- ceptional difficulty of keeping stoneless plums and prune seeds in condition for growing. Not having the natural protection of the shell, they tend to germinate too early, and of course are peculiarly subject to the attacks of insects and — of fungous diseases. Such seeds may best be placed in cold storage as soon as collected and cleaned, and kept at freezing temperature. Seeds thus cared for will sometimes germinate almost as quickly and readily as beans or corn. They must not be planted too early in the spring, lest thelr: too. grompt germination ae to injury from late frost. Incidentally, Tsay note that quien ealiele . me from cold climates have been observed to — start with greater promptness and grow bet- — ter than those from our own immediate vicinity _ where the winters are mild. Cold seems to rest — the tissues and prepare them for rapid growth, — just as treatment with narcotic drugs has been — observed to do in certain interesting experiments _ that will elsewhere be referred to more at length, — Out or Door PLaNtTING og i In California, plum seeds are usually planted — in January or February, in a little furrow about — an inch deep. A furrow may be made accurately — QUANTITY PRODUCTION 281 and expeditiously with the aid of a triangular bit of board an inch or so wide nailed across another longer piece, so that when drawn along a garden line it makes a narrow furrow of exact width and uniform depth throughout. Plant the seeds about one-half inch to an inch apart, and cover with a thin layer of soil; then fill the furrow with sawdust. This is an impor- tant matter with cherry and plum seeds, espe- cially with the stoneless ones which must be given every inducement to push through the soil. A heavy, compact soil placed over cherry and plum pits prevents a large number from pushing up to the light. For this reason a sawdust covering is preferred, and it also regulates the moisture with exactness, allows for sufficient aeration, and equalizes the temperature. Moreover, the saw- dust is distasteful to slugs, thrips, cutworms, and other insect pests. Peach, nectarine, and apricot seeds are planted farther apart and a little deeper; quince, pear and apple seeds are planted about the same as plum seeds, both as to distance and depth, or in large lots may be rather thickly sown in drills or furrows six or eight inches wide and eighteen to thirty inches apart. For growing seedlings of conifers—pines and their allies—cold frames or shallow boxes are . et Ee graft and the Keay, «varity of Prana flora, upon which the graft was growing. — * There was a most perfect balance in foliage, fruit, and growth so far as I could judge. One of the new seedlings was light purple in foliage — throughout the season. Its fruit was small, — nearly globular, and purple in color even when only half grown, while the Kelsey is an extremely, Absolutely everything about the appearance of this strange seedling seemed to suggest that it was a cross between the purple-leaved im- ported plum and the Kelsey. There was no other purple-leaved plum within thousands of miles. The cion had not bloomed, and so cross- ing could not by any possibility have maaan in the ordinary way. (There 4s no tecape: trom sthe ose | this was a case of so-called Peaperesne ri very existence of which has been doubted. | The purple-ledved cion had without doubt ‘ets fluenced its host in such a way as to prodase what was a hybrid progeny. The new purple-leaved seedling was grafted upon an old tree, and in due course I produced several thousand second and third generation offspring from the original seedling. The fruit is of a characteristic red color, and in flavor GRAFTING AND BUDDING 307 closely resembles the fruit that the original purple-leaved cion subsequently bore. In size the fruit is intermediate between that of the purple-leaved cion and that of the Kelsey. The descendants of this hybrid stock vary in the second and succeeding generations, just as they might be expected to do had they grown from a hybrid seed produced by pollination; thus affording additional evidence that we have to do with an actual case of sap-hybridism. GRAFTING TO SAVE SPACE AND TIME This record is made at length because of its extreme unusualness. Never in the entire course of my wide experi- ence have I seen another case in which I could trace such definite influence between the grafted cion and its foster parent. And so we may take it as a safe general rule that a cion, however grafted, will retain the charactéristics of its parent stock, and that the tree on which it grows will be fundamentally uninfluenced, so far as the character of its fruit is concerned, by the graft. - It is not at all with the expectation of influ- encing the fruit product of either cion or stock that the familiar process of grafting is resorted to. The chief object of grafting, as practiced 908 LUTHER BURBANK < save time. ta ee ee : obvious that where hundreds of grafts from — s aieche on sas eoniah sc | ments ameng these, hundred THE Senses or Insects er a It is needless to multiply instances of the wonderful adaptations of form through which the various species of plants have made sure that the insects: for ‘witch ‘neces Se carry out their part of the bargain. Some flowers have long tubes which only the coiled proboscis of a moth or the slender bill of a humming bird can fathom. These are sure — to provide pollen carriers of a bulky character which only humming birds or large insecis like the moth could transport. Mechanisms are even _ provided to exclude from the nectar chamber — bens and other smell ae ee ‘s service to the flower. A But such cases, while in the augeegellealale , ous, are on the whole exceptional. In general the — plants with which the horticulturist deals, and par- — ticularly the plants of the temperate zone, have contented themselves with a much more simple arrangement, whereby the pollen bearers are so arranged that any small insect that visits the flower is almost sure to go away laden with pollen. But, in particular, provision has been made by the vast majority of flowers of the orchard anal eran Soret Se ee the bee. BEES DO THEIR WORK 343 This familiar insect, the one member of its vast tribe that is very directly helpful to man as a producer of food, is the indispensable coadjutor of the most important varieties of cultivated plants. Bees of one species or another are the universal distributors of pollen in orchard and garden. The beautiful flowers that the apple and plum and cherry put forth, and the perfumes they exhale, are primarily designed as advertise- ments for the bee and the bee alone. Whoever realizes this truth will not be likely to doubt that the bee, in common with other in- sects, has good olfactory organs and an eye for the discernment of color. Yet there have been entomologists, even in recent times, who have questioned whether insects really have the sense of smell, and others who have challenged their color sense. As to the latter point, whoever has taken the trouble to observe the maneuverings of an in- dividual bee in the flower garden, and has seen it pass from one red flower to another, quite often confining its visits exclusively to blossoms of one hue, will have gained sufficient evidence that the bee is by no means color blind. As to the sense of smell, if further evidence than that supplied by everyday observation of the visits of insects to perfumed flowers were required, it is furnished by an interesting and remarkable experiment made by Professor Jacques Loeb, formerly of California Uni- versity, now of the Rockefeller Institute in New York. Professor Loeb placed a female butter- fly in a cigar box. Closing the box he suspended it in mid-air between the ceiling and Boor of « room, and opened the window. “At first,” says Professor Loeb, “no butterfly of this species was visible far or near. In less than an hour a male butterfly of the same species appeared on the street. When it reached the high window its flight was retarded and it came gradually toward the window. It flew into the — room and went up to the cigar box upon which it perched. During the afternoon two Cilia of the same species came to the box.” A commentator observed that the annual makes it unequivocally clear that insects possess an olfactory sense of almost inconceivable deli- cacy. But the question as to what is the real character of the stimulus that produces the sense of smell is one of the mysteries of science. : “A substance like musk,” he says, “may give out a characteristic odor continuously for an in- definite period, while the substance itself appears to lose no weight. If particles of the odoriferous substance are really thrown off, these particles BEES DO THEIR WORK 345 must be almost infinitely tenuous. If, on the other hand, the stimulus is due to the giving out of waves or vibrations comparable to the waves of light or of sound, the nature and other charac- teristics of these manifestations of energy are absolutely unknown.” Another experimenter has shown that ants will follow a trail that has been made by other ants bearing honey or sugar. The inference seems obvious that the ants are following a very delicate trail by the sense of smell. But perhaps it is well, considering the unrevealed nature of the stimulus associated with odors, to adopt Pro- fessor Loeb’s cautious phrasing and speak of the sense through which insects are guided to odor- iferous objects as “chemical irritability.” The fact that a bee is able to travel in a straight line backward and forward between its distant hive and the flower bed or the apple tree from which it is harvesting, even though the distance be a matter of miles, suggests the possession of organs of sense of a far more delicate character than our olfactory nerves. It is hardly probable that vision is an impor- tant aid in these long-distance flights; for Pro- fessor Loeb’s experiments have led him to infer that the dioptric apparatus of insects is very in- ferior to the human eye. Moreover the flowers A HYBRID EVERGREEN This is a cross between the cypress and the juniper. Our evergreen trees somewhat frequently hybridize in a state of nature, This is not strange, considering that the conifers send out Shei pollen. (a. clouds, 49. 04: ag at random by the winds. BEES DO THEIR WORK = 347 would scarcely find it necessary to put out ex- pensive corollas and deck themselves in gaudy colors if their signals were meant for creatures having very acute vision. In point of fact, the complex multiple eye of the insect, devoid of any such adaptive apparatus for focusing as the lens of the mammalian eye, does not suggest acuteness of vision, but rather a more or less vague appreciation of large masses of color. The recent experiments.of Dr. Charles A. Turner, of the St. Louis Academy of Science, have, indeed, demonstrated that bees can disting- uish between color patterns as well as between different colors. But, although the tests of the naturalist Plateau, which seemed to show that insects are attracted solely by odor, are thus con- troyerted, it doubtless remains true that the sense of smell—or some equivalent sense of a kind as yet unanalyzed—is the chief guide in bringing insects from a distance to the vicinity of flower bed or fruit tree. Professor Loeb declares that the “chemical irritability” of the insect, as excited by odorifer- ous objects, is immeasurably superior to the sense of smell of human beings, and possibly even finer than that of the best bloodhound. Observation of the honey gatherer making his “bee line” from 348 LUTHER BURBANK | hive to orchard and back again prepares us to accept this statement at its full valuation. There must even arise a question as to whether the insect’s equipment of “chemical irritability,” or whatever it may be called, ot the possession of a sixth sense. AIDING THE Bee We have instanced over and over the vital importance of the process of cross-fertilization which the bee accomplishes for the flower. _ It may be of interest to cite a few familiar illus- trative instances of devices adopted by certain familiar flowers to make the services of the bee surer and more effective. Inasmuch as the bee has no conscious share in the plant’s solicitude to effect cross-fertilization, it has been found expedient on the part of many flowers to adjust the arrangement of stamens and pistils in such a way that the visiting insect shall surely receive a modicum of pollen, yet cannot rub this pollen against the stigma of the same flower. : Some illustrations of what might be called extreme measures to prevent such inadvertent self-fertilization were given earlier in the present chapter. Let us note a few additional instances, with reference in particular to flowers that are largely pollinated by the bee. BEES DO THEIR WORK — 349 A simple and effective method of guarding against self-pollination we have seen illustrated in the common geranium (Pelargonium). When the geranium flower first opens, a little cluster of anthers may be seen on the tip of the erect filament in the center of the bright, showy flower. At this stage the undeveloped stigma lies closely folded up and wholly unreceptive among the stamens. But soon after the pollen has been shed or gathered, the anthers drop off; then the stigma spreads out its five receptive lobes from the tips of the connecting filaments, and is ready to receive pollen from another flower. In the snapdragon (Antirrhinum), and in many other related plants, the anthers lie along the roof of the corolla tube, where they are brushed by insects that pass down the tube in search of nectar. The stigma holds a similar position, but is farther out toward the mouth of the tube. The stigma is a very interesting structure; it is composed of two flattened lips, which respond to the slightest touch. When a bee, after visits to other flowers, enters the tube, the hairlike appendages on its back brush against the lower lip of the stigma, and the irritation causes the lips to close quickly and tightly together, coming thus in contact with and scraping the pollen-dusted back of the bee. with a fresh ut of pollen from slisieoias panion anthers. But a few min the stigma lobes open again, like a trap set for the next visitor. eG DARD ; str won, a ane ohne o The foxglove (Tiigitalie) leo hex slalaaaaulal pistils lying along the roof of the corolla tube. Its device to prevent self-fertilization is the less ingenious but equally effective one of ripening the stigma enly ether the: pole =e The Spanish broom (Spartium junceum) is a typical butterflylike flower, that, in common with others of the same family, has developed a peculiar mechanism to bring about cross- pollination. The two lower petals are joined together into a keel-shaped structure that con- nects the stamens and pistils. The other three petals are more enlarged, and are spread to i BEES DO THEIR WORK = 361 make a more effective advertisement, challeng- ing the attention of insects. The visiting bee naturally alights upon the projecting keel. The weight of its body presses this downward and the stamens and pistils, by a springlike action, are thrust out against the body of the insect, scattering the pollen freely. Thus the stigma may become covered with pollen that the bee has received from some other flower while the anthers supply a new coat of pollen for future distribution. Still a different arrangement is that of the common iris. Here the anthers lie in a fold of the large petallike branches of the style. The stigmatic surface is confined to a little crescent- shaped patch near the tip of the style branches, and is protected by a thin, sacklike shield. The structure of the flower is such that an insect as it passes down the petals on its way to the _Nectary, brushes against the anthers and dusts off the polien. As the insect passes out, the stigma shield protects the stigmatic surface completely. But as the insect visits another flower, its pollen-covered back comes in direct contact with the edge of the stigmatic shield and the pollen is scraped off against the receptive surface. 352 LUTHER BURBANK | These, then, are familiar Mustretions “all ‘the. really wonderful adaptations through which it comes to pass that the bees carry out eir part of the ancestral compact that insures the plant such interchange of pollen as is essential to racial — progress. Perhaps the most alluring feature of — the entire coalition is that the bee rms its all-important function unwittingly in the course of the quest of sweets that appeal to its appeti There is no compulsion in the matter; the pla And to add to the satisfactoriness of the arrangement, from a human standpoint, it m be recalled that the efforts of the industric insect, which thus nankes pusstile shi auunal plant experimenter, result at the same time storing the nectar gathered from the flowers form one of the most delectable of foods. __ eth on Suga pa ihren fa: oe | PLEASE DO NOT REMOVE | CARDS OR SLIPS FROM THIS POCKET _ UNIVERSITY OF TORONTO LIBRARY Me pe