Popular Science Monthly/Volume 67/August 1905/A Visit to Luther Burbank
| A VISIT TO LUTHER BURBANK.[1] |
By Professor HUGO DE VRIES,
UNIVERSITY OF AMSTERDAM, HOLLAND.
FOR many years I had wished to make a study of fruit culture in California and especially of the production of new varieties. One reason which, more than others, made me decide to accept an invitation to visit California was the prospect of making the personal acquaintance of Luther Burbank.
Burbank is the man who creates all the novelties in horticulture, a work which every one can not do. It requires a great genius and an almost incredible capacity for work, together with a complete devotion to the purpose in view, to accomplish such results. Burbank possesses all these qualifications, and his previous achievements have excelled all expectations to such an extent that it is rightly presumed that no possible improvements are beyond his reach. In fact, the most impossible things are attributed to him, and the credulous American people expect from him novelties which any person who knows would immediately declare to be nonsense. I once had a conversation, in a Pullman car, with a lady and a gentleman who told me all kinds of interesting stories about plants and fruits, about climate and places and many other things. They knew, of course, Burbank. Every American does, who pretends to know anything about fruits. They told me all about the large and juicy plums, the new pears, the beautiful flowers, and a number of other creations of his. But by far the best and most delicious fruit, entirely new in form, color and flavor, was, they said, a hybrid between a raspberry and a mulberry! Over this mystic novelty her enthusiasm was inexhaustible!
As soon as I had decided about my plans I wrote to Burbank and told him my desire. I had previously been in correspondence with him, and a few years ago I had hoped to meet him at the Congress of Hybridologists in London, but his arduous labors prevented him from being present. I feared even now that there would not be many chances of speaking to him, because July is his busiest time, when all the numberless crossings are made and the selection of prunes takes
place. These fruits at the present time are represented by a larger number of varieties than any other plant in his orchards. It is no small matter to select the best plum out of 300,000 different varieties. This requires not only talent and experience, but also a great deal of time, and it all has to be done within a few weeks while the prunes are ripe on the trees.
My wish to see him was, however, met with the greatest cordiality. Others had naturally the same desire, and we were consequently all invited to come together to Santa Rosa, where Burbank lives, and to inspect, under his personal guidance, his experimental plots. He set apart an evening and a whole day for our visit. How many crossings and selections he had to sacrifice for this I do not know. Our party was a rather large one. There was first Professor Svante Arrhenius — the man who with van't Hoff laid the foundation of modern physical chemistry. Among all the savants I ever had the fortune to meet, he certainly is the man with the widest knowledge and the broadest interests, and his opinion about Burbank's methods was of the greatest value to all of us. In our party was also the physiologist, Jacques Loeb, the discoverer of many important phenomena in regard to fertilization in lower animals. His studies have led him to the question of the causes of life and of those life-functions which give animals and plants their characteristics, expressed in the differences of kinds and varieties. These characteristics can not be studied to advantage except by means of hybridizing. So far no one in the whole world has made crossings on a larger scale than Burbank, and it was only natural that there should be many points in common between the studies of both these men. Our party was under the guidance of Professors Wickson and Osterhout, of the University of California. Both are personal friends of Burbank and, notwithstanding the distance, often visit him to keep posted on the progress of his work.
Americans, and especially Californians, feel a great deal of pride in their Burbank. He is a very modest man; he does not work for fame, or for honor, or for the acquisition of wealth. He has none of the aspirations of a merchant. He loves his plants, and is enthusiastic over his work and plans. To accomplish something great for his country is his ideal. For his personal self he is satisfied if his work furnishes him a living and enough to carry on his experiments.
In outward appearance Burbank is a very plain man, more a gardener than a savant, with clear blue sparkling eyes, full of life and fun, appreciating humor in others, telling us stories that kept us constantly laughing. He lives in a small house with his mother and sister, and has but one servant on the place, as he does most of the work personally. The walls of his room are covered with small photographs of his victories, and during our visit these pictures were taken down and demonstrated to us.
As a matter of course prunes interest him more than anything else. Of the hundreds of thousands, which he got by crossing, a few are already in the market. To give an idea of the interest connected with such a new kind I may only name the Waynard plum. This is a delicious, big and round, dark blue fruit with a taste that makes one think of a peach. One seedling of this tree, the selection from hundreds of thousands, he sold to a company, formed especially for the purpose of multiplying and introducing it into the market. This company was not to raise crops from it and to sell the fruit, but to produce grafts
and as many plants as were required to introduce it into those states of North America where it will thrive, to make it one of the most commonly cultivated trees in the United States and thereby to add millions upon millions of dollars to the annual production of the country. How much Burbank realized for this one seedling he did not mention to us, but it was certainly enough to compensate for his entire plum-culture of many years.
Such are Burbank's ideals. For himself it is sufficient to receive the cost of producing his creations. He has no children, and does not feel the necessity of accumulating money. The sole aim of all his labors is to make plants that will add to the general welfare of his fellow beings. Therefore he looks in his selecting for other qualities than those upon which we, in Europe, generally lay stress. 'Shipping qualities,' that is the ability to withstand handling in packing and shipping by railroads or vessels, are most important to him. Next comes the property that makes it possible to cultivate them in regions which previously have been unsuitable for this purpose. To produce varieties which combine with great productivity a sufficient degree of frost resistance is one of the chief aims of Burbank.
As an example of this, he spoke of his crossings with the Beach plum (Prunus maritima). Here and there along the coast, especially in the eastern states of North America, this shrub grows wild. It is satisfied with almost any conditions. The most infertile sandy soil is just as good as the richest loam; the driest place as agreeable as the temporarily inundated ground. On the eastern coast it thrives equally well in the north and in the south, being nowhere affected by the climate. It never suffers from frost, and always forms a dense shrub, often to the exclusion of all other tree-growth. In addition to all these qualities it is immensely prolific. It does not, of course, produce any edible plums; the fruit is of the size of a small cherry, with a large seed and a very thin layer of fruit-flesh. Late in the season the branches are bent down under the weight of the fruits, which cover the branches in great profusion. This plum has, further, a great number of varieties, with all kinds of forms and colors, some ripening in July and August, others as late as September or October. Even in taste there are differences. Although the fruit is uneatable, it is possible to judge about its flavor.
In many parts of California water is very scarce, but still the soil is fertile. In such regions the population is scanty and remains so, limited by the available water supply, in spite of the perfect climate and the fertility of the soil. Some kind of fruit tree that by means of long roots is able to get water from the deeper strata would be a blessing to such regions. Wealth and prosperity would increase and a large population could exist where lack of water now prevents cultivation. Burbank thinks he will be able to produce such a fruit tree by combining the deep-rooting tendency of the beach plum with the delicious flavor and richness of our common plums. He brought to his place all kinds of beach plum in order to cross them with other species. His aim will not be accomplished by one crossing. Connecting links are required, and therefore the North American beach plum has to be crossed with other American and Japanese plums (Prunus triflora and P. Americana), and each of these hybrids with four or five kinds of the common plum. Finally a series of hybrids is developed from which almost anything can be expected.
It is natural that by such crossing we must expect the appearance of undesirable characters as well as desirable ones. Some plants produce only good, others only bad, characters, but the greater part exhibit some good points in connection with a larger or smaller number of undesirable qualities. From hundreds of thousands only those must be selected which possess all the desired characters. To make this possible it is necessary not only to cross six or eight kinds with one another, but to use as many sub-species and varieties as possible for the experiments. This work necessitates hundreds and even thousands of experiments. The result of each crossing can only be judged by the fruit, and this indicates new combinations. It can easily be seen what an immense amount of work, patience and capacity of judgment and choice is required to reach the ultimate aim. Yet Burbank told us on that remarkable evening of many such instances. He was enthusiastic in his hope to be able to realize all this during his life.
The making of hybrids from the different species of plums naturally brought us to a subject which, for me, was of the greatest importance from a scientific standpoint. As Arrhenius and Loeb also felt more interest in the theoretical side of these problems, I took the first opportunity to bring the conversation to that point.
I had in mind the 'pitless prune.' Just imagine this, reader! Next day Burbank took us to a plum tree heavily loaded with clear blue, very attractive, yet small plums. He picked a few and asked us to bite right through the middle of the fruit. We did as requested, and although we knew there was no stone in the plum, we experienced a feeling of wonder and astonishment. Inside the plum was a seed, like an almond in its shell, and with the taste of an almond, but without the stony covering. When cutting through the fruit, we found the seed surrounded by the green fruit-flesh, the innermost part of which was a jelly-like mass, in which could yet be seen some remnants of hard little stones, that scarcely offered any resistance to the knife. Burbank declared, however, that he was not at all satisfied with the result, and said that he had already young trees with fruits, in which nothing could be detected of the stone.
Osterhout told us about the impression this plum made on Professor Bailey, professor of agriculture at Cornell University. He came unprepared before this tree, and Burbank, always full of humor, thought it a good opportunity to play a little trick. Bailey had declared that a stoneless plum was entirely an impossibility, something that was outside of one human lifetime; he refused to believe the statement and could not be induced to risk his teeth on the experiment. To the great amusement of Burbank and Osterhout, he took a knife from his pocket, commenced to peel the plum and to cut away the fleshy part, in order to expose the stone, which he was sure would be there. How great was his astonishment when he finally did not find anything but the naked eatable kernel!
A couple of years ago when I read in one of Burbank's price lists about a stoneless plum, I shared a similar astonishment. How was it possible to bring about such a great change? Hybrids do not present, as a rule, any new simple qualities, only new combinations of already existing properties. The evident properties are often developed from more than one factor, and such composite characters may thus appear, without any new essential factors having been present. This is a fundamental principle in crossing, whether it is done for scientific or for practical purposes. But although the elimination of the stone is only a loss and not a gain of a character, such a loss is just as much outside the sphere of hybrid making.
My astonishment was, therefore, as great as that of Bailey, and I had long ago made up my mind to ask Burbank, if I ever had the opportunity, what secret method or what happy coincidence had enabled him to effect such a fundamental change in a plant. I put my question to him that evening, convinced that on the answer depended largely the scientific value of our visit. And for the second time I was surprised over the unexpected and simple reply: "About two centuries ago they knew in France a 'prune sans noyau' and I bought the fruit and raised a plant in order to cross it with others of my prunes." Thus there is no exception to the rule, there has been no real production of a new character, but we have only had a case of the general American principle: 'try everything.' Over the whole world Burbank looks for different kinds and varieties of prunes, no matter how insignificant they may be, however wild and uneatable, as long as they possess only one or another characteristic, which, in combination with the common kinds, may bring out a new variety of greater value.
To Professor Loeb and myself this was, to a certain degree, a disappointment. We had expected to learn a great deal about this point, the fundamental idea, if not the ultimate aim, of the studies of both of us—that is, the question of the nature and origin of new characters. We now surmised that Burbank's experience did not throw any light on this question.
I had before experienced a similar disappointment. About twenty years ago I was occupied with experiments on hybridization for horticultural purposes. I had already found at that time the general principle that only combinations, but no primary characteristics, were produced. Only in one instance I encountered what seemed to be an absolute exception to this rule. It was an announcement of Lemoine of Nancy, the most celebrated breeder of garden novelties in France. He claimed that he had been able to produce by crossing double lilacs. Double flowers remain longer on the branches than the single, which usually drop off after a few days. To find out how it was possible to develop by crossing from single lilacs new varieties with entirely new characteristics I visited Lemoine in Nancy. Walking through his gardens. I put the question to him and received the following answer:
"That is very simple. As a boy I had seen in the garden of an old relative a specimen of Syringa azurca, a very rare lilac of an ancient type with double flowers. Remembering this, I bought that tree from the person who owned my relative's home. With this tree I crossed all varieties of single lilacs I had and got the double variety." Here we find again the same procedure: first buying, then crossing, later grafting or budding on other forms, but no creation of an absolutely new character. The number of combinations may be unlimited, yet the creation of new prime characters is entirely excluded.
This principle came into full evidence while we were in Burbank's grounds. He demonstrated to us 'white blackberries' with large fruit of a delicious flavor, which now are an article of commerce. I asked him about the origin of this crossing. Burbank explained that here and there in California occurred a wild blackberry with white fruit. He had crossed this plant with other forms. A white variety of the common raspberry has similarly been known in Eurpoe since olden times.
Another striking example is furnished by the spineless cactus, one of the novelties of which Burbank expects much. It is one of the Opuntias, a desert plant, the fruit of which is eaten and known as Indian figs. Its stem consists of big, flat slabs, joined together in the most fantastic manner. It reaches a height of six feet, spreading widely and growing luxuriantly. The fruit is much relished by cattle, as it is juicy, rich in foodstuff and has but few thorns. The whole plant is eaten by animals only when they are driven to do so by hunger, as it is covered with hard prickly thorns. If the plant is cooked for some time the thorns soften and the cactus becomes a nutritious food. This process of cooking is, however, too expensive for practical purposes, and hence a cactus without thorns would transform a barren desert into rich pastures. To reach this Burbank brought together wild Opuntias from Mexico, South Africa and various other countries as well as the commonly cultivated species. Among the specimens Burbank received, one was accidentally found without prickles on the Leaves and another with no thorns on the young shoots. It was, therefore, necessary to combine in one plant both these negative characteristics, something that experience has shown can be done. However easily this is explained, still it elicits astonishment and wonder to see a cactus without spines. All that is now left to be done is the crossing with forms known as the most nutritious, and at the same time to watch the development of other characteristics, especially the root system. It will not take many years for Burbank's cactus to transform large stretches of desert into fertile fields even without irrigation.
Along the road in front of Burbank's house is a long row of high trees with wide spreading crowns and dark foliage. These are Burbank's first hybrids, walnuts, that are a combination of the eatable nut and an ornamental tree of the same genus (Juglans regia nigra). From seeds of this hybrid Burbank raised a few rows of seedlings which show a surprising variety in growth and leaves. These latter are all lanceolate, sometimes with broad leaflets, sometimes with narrow, some are petiolate, others sessile on the branchlets, now coarse and then fine, frequently reminding one of the common English walnut, and again approaching the ancestor, the black walnut. We saw some of the variety of forms resulting from crossing, and from these the best have to be selected for certain purposes.
Burbank's entire garden contains only two and a half acres, while the experiment farm near Sebastopol, about one hour's drive from Santa Bosa, comprises twenty acres. Two days each week Burbank spends on the farm, riding there on his bicycle; the rest of the week he is at home. Here are all the more delicate crossings, and it is here every new experiment is started. It is only when certain definite results are in view and when the cultivation of thousands of specimens is required that they are raised on the farm near Sebastopol.
He showed us a bed of wild flowers in his garden. He collects these in the vicinity, transplants them, selects and crosses the various forms as soon as they promise anything of advantage. Others he crosses with cultivated species of sufficient relationship. His idea in doing this is to make a large number of garden plants, which will be so fertile, and consequently so cheap as to come within the reach of any one. Briefly, he wants to spread over every garden spot in California a still richer treasure of flowers than it already possesses. Thus, for instance, he has crossed the large and deliciously night-scented Nicotiana affinis with the wild, tree-like Nicotiana glauca, which can not be called an ornamental plant on account of its greenish flowers, but by flowering profusely and by having such large bunches of flowers, it offers an excellent object for hybridization. We noticed several kinds of Cape gooseberries (Physalis), of the blood-red Heucheras and others already hybridized. The common garden poppy (Papaver somniferum) he had crossed with the large flowered, brilliant orange-red, perennial poppy, and a great number of hybrids were now growing. These were almost all sterile. Some of them terminated in a dried-up stub without flowers, others had a minute rudiment of fruit, others only remnants of calyx and corolla. There were all stages up to normal flowers, and seed capsules in which the not yet fully developed seeds could be seen through a lens.
After crossing all kinds of color varieties of the common poppy he got one with a light blue color. Although the color is not very pretty, yet this plant is very interesting, as blue poppies have been hitherto unknown. Probably the change in color is caused by the combination of pigments in some flowers and the chemical constituents of cells of others. This is, however, only a supposition.[2]
Many other wild plants, as Brodiœas, Erysimums and Cephalyptrum Drummondi, he had hybridized, getting flowers which first came out carmine red, but then slowly changed to white, a very unusual mode of variation. In order to reduce the price of Amaryllis and Gladiolus to a few cents, and thus make these beautiful red and white-striped flowers common in every garden, he devoted attention to the increase of side-bulbs. He had already plants with twenty to twenty-four bulbs instead of the old forms with hardly any or but a few side-bulbs. Burbank has his own peculiar ideas about the power of nature and natural phenomena, which play such an important part in his work. His principal theory is that 'heredity is the sum of all past environments'. This he repeated time and again in his explanations. Crossing brings together in one individual the sum total of the environmental influences to which the two lines of parents have been subjected, and hence increases its variability.
Among the remarkable results of Burbank's work which we saw at the Sebastopol farm were a couple of trees of Loquat (Eryobotrya japonica) about six feet high, but with spreading fruit-laden branches. One of these trees was the original Japanese kind with small yellow fruit, the size of a cherry, of acid taste and almost filled with the large seed. It has a peculiar flavor, found in no other fruit. This aroma was also found in the fruits of the other tree, but these were larger than walnuts and had an orange-red color. The seed was not larger than that of the wild tree, but the juicy fruit-flesh was greatly developed in thickness and very delicious. This improvement of the loquat, which fruit makes one of the finest delicacies for the table, was accomplished by Burbank without crossing, by selection only. This is the same process by which, since the time of the celebrated Belgian horticulturist, Van Mons, our large and juicy apples and pears have been produced, that is, by sowing the seed on a large scale and then continuing the selection for one or more generations. About one half of Burbank's grounds was taken up by prunes. He has at present about three hundred thousand different kinds. The number of trees is not so great, however, as he grafts his seedlings on other trees, when they are two or three years old and show some promise for the future. For this purpose he uses the whole seedling, throwing away the roots. We saw small trees with from thirty to forty grafts, and large ones upon which two hundred to four hundred branches were grafted. When the foliage is of different color and form and the branches bear plums, red, yellow or blue, flat or round, small or large, some ripe and others only half developed, the result is strikingly bizarre. When the fruit is ripe he walks along the rows, marking those which are undoubtedly the best, as far as can be judged by a cursory examination. Then a workingman removes all those which for one reason or another are considered valueless. By this method only about half of his original stock is left, and this then receives his careful investigation. Possessed of an inborn talent, he is able to select in a few summers four or five of the best kinds among the hundreds of thousands on his grounds. These are then multiplied, while all the others are destroyed and replaced on the mother trees by the next series of seedlings. These are often somewhat assorted even before transplanting from the shallow boxes where they have been grown. Sometimes the color of the leaves indicates the value of a tree, as in crossings between the common cherries and prunes with Prunus Pissardi, which, on account of its brown foliage, often is cultivated as an ornamental tree. In other cases the size of the leaf is an indication of certain properties of the fruit, Burbank's long experience enabling him to see some correlation between leaf and fruit. Thus he can with some certainty discard a number of trees before transplanting, which naturally saves time and room.
One of Burbank's favorites is a large 'Marguerite,' which he calls the 'Shasta Daisy,' after the great California mountain of that name. It is one of his improvements of a perennial daisy which grows wild in Shasta county, and is very variable. By crossing and selecting, it has been developed into a plant that excels by its rapid growth and its profusion of extremely large beautiful flowers, which for months cover the ground. These and other characteristics will make the Shasta daisy one of the commonest and cheapest, still one of the most beautiful, of garden plants.
What makes Burbank's work entirely different from that of other plant breeders is the immense scale on which his selecting is made. He is, therefore, able to make greater improvements than others and in much shorter time. In his work Burbank is guided by a special gift of judgment, in which he excels all his contemporaries. The best proof of this is to be found in the great success his creations have made, not only in North America, but also in Europe.
His methods of work are the same as those followed by plant breeders in Europe. Secrets he has none, and if he is not willing to demonstrate his cultures to everybody, this must be attributed to the fact that his time is too valuable. There is no fear that any one could 'steal his trade' by merely looking at it. Every one is left free to follow in his path, but without the special disposition for it nobody will succeed, and for simple imitation the entire process is too complicated.
To give an idea of the immensity of his cultures, it is sufficient to cite one instance. When selecting a new kind of blackberry he picked out the best from 60,000 specimens, all in full bearing, dug up the rest and burned them. This is his way of working, not only with one kind of fruit or flower, but with all. The most remarkable trait, however, of his work is that he experiments with as many forms as possible. This method is carried to the highest degree of perfection, and thereby his results are so stupendous that they receive the admiration of the whole world.
However large may be the number of forms subjected to crossing and selecting, this method is in itself limited. Burbank's products are all, with a few exceptions, reproduced not from seed, but by vegetative propagation. Grafts or cuttings, bulbs, shoots or division of roots are the means of multiplication. It is well known that vegetative propagation results in much greater stability than raising from seeds, which often produces degenerate types. Because of this fact, Burbank hardly ever experiments on annual or biennial plants, but confines himself to perennials.
In Burbank's methods selection plays the most important part. To accomplish a good selection, however, the greatest possible degree of variation is a prerequisite. This variation is attained mainly through selection of the starting points and through artificial hybridization. The results are next cultivated on a large scale under environmental conditions which will develop as many differences as possible.
Varieties coming from separate localities differ not only in regard to external characteristics, but their capacity of modification varies considerably, and can often be ascertained only in the special environments of an experimental garden. The greater this power of adaptation the more chances for the experimenter.
As a general rule, it holds true that the results of crossing depend primarily on the selection of varieties used for that purpose. These indicate, so to say, the program, the list of possibilities from which the choice and the combinations have later to be made. Outside of this list very little good is obtained, and then only by accident. This occurs very seldom in Burbank's cultures.
When he wishes to experiment with wild flowers Burbank goes out himself in search of specimens. He carefully compares the different places of growth and investigates the variation in individuals. Many days are thus employed in gathering together one kind in order to find out existing dissimilarities or to see whether they promise anything for future cultivation. Such specimens are then transferred to his experimental grounds, and when established are subjected to crossing.
With crossing or hybridization we usually understand the sexual union of two individuals belonging to different species or varieties. In practical plant breeding, however, it is not sufficient to combine two types, but three, four, and even five or six kinds are thus united, so as to bring out as many desirable qualities as possible in one single variety. It is, of course, impossible to predict what result will be obtained, and it must be left to chance and the future to decide what combinations are the most desirable. Often crossings are made only with the object in view that among all the combinations something good may turn up. In this case the breeder wants to destroy the equilibrium of existing characters, to make the constant forms unstable, and then to select the best out of the many balancing properties. When the parents themselves are variable their offspring will naturally be more so, and the number of differences increases with the number of hybrids experimented upon.
There is also a chance that latent or sleeping characters may be brought to light. From a scientific point of view we know, as yet, nothing about this, but Burbank holds the opinion that in many cases one character prevents another from becoming visible. For instance, in crossing, the first one meets an opponent which has kept it back—as is often the case in the crossing of varieties—and this latent character gets an opportunity of becoming active. We can naturally not detect what dormant qualities are hidden in a plant, and may, therefore, expect all kinds of surprises. The combinations may be desirable, and the hybrids can be propagated immediately, or they may be the reverse and need further crossing before the unfavorable traits are eliminated. Unknown atavistic properties may in this way become evident and may play an important part in the development of future generations.
In other cases the crossings are made with a certain purpose in view. These are the instances from which we learn the most, and which at the same time give the best chances for quick and favorable, results. A certain number is selected of species or varieties, which together contain those characters we want combined in one type; the undesirable properties we try to eliminate. As the crossings result in all kinds of combinations, it is necessary to produce them in as large numbers as possible, so that among the numberless undesirable and imperfect plants we may choose the best. The chances are that from the five or six desired good characters only three or four are found together. Thousands of seedlings have to be developed in order to create a possibility of finding one form in which the expected qualities are present. It is a game of solitaire on a large scale. I may mention as an example of this the production of the Alhambra plum, which was obtained by combining European, American and Japanese kinds. It took thirteen years to combine all these. First came the crossing of the Kelsey with the Prunus Pissardi. Their hybrid was crossed with French prunes. In the meantime various other crossings were created, and it was made possible to work the pollen of these 'into the strain' as the term is called. First came Simoni triflora, and then Americana nigra. This sevenfold combination gave us the variety now known in the market as the Alhambra.
We can go still further and cross species that are yet more widely separated. It is then naturally even more difficult to predict the results. Burbank endeavored to combine the plum and the apricot and succeeded in getting a new fruit, which he calls plumcot, of very delicious taste and looking very much like an apricot, but combining the soft skin of this fruit with the dark color of the plum. Burbank had a number of varieties of this new fruit, some with a yellow fruit-flesh, others of dark red color, light rose or white. In taste these plumcots differ considerably.
Burbank is equally successful in hybridizing flowers. In the instance of the Callas—well known through the many varieties of Richardia aethiopica—all the new cultivated forms have been hybrids of a few species. Burbank, however, crossed Calla hastata, the yellow 'Pride of Congo' C. Elliottiana with dark yellow flowers and spotted leaves, C. Pentlandi, also yellow with dark purple spots, the rose-colored C. Rehmanni, and the small light yellow C. Nelsoni. From all these he received a great number of different hybrids, among which were found the most varying shades of color, very large-sized as well as dwarfish forms. The colors were not limited to spadix and spathe, but spread over peduncles and petioles, and even the leaves were variegated with spots and stripes. In addition to these peculiar colors and forms the hybrid Callas, of which Burbank had long rows in bloom at the time of our visit, possess a hardiness and adaptability to extreme temperatures, which fit them for outdoor cultivation, where formerly Callas could be forced to full development only in hothouses. Every year these hybrids are again subjected to the process of crossing, and each year new and often unexpected forms appear. How far this will go it is at present impossible to predict.
Because of the favorable climatic conditions under which Burbank conducts his experiments, he is able to work on a much greater scale than is possible in Europe. While we can only select from a few hundred of seedlings, Burbank can get tens of thousands into blossom. In this way the number of years necessary to bring about improvements can be considerably reduced. It required in Europe more than half a century to produce the beautiful Amaryllis forms, which we admire so much. Burbank has got wonderful results in much shorter time. In the process of selecting he preferred those forms which required the shortest time to come into blossoms, and by following up this method he succeeded in greatly shortening the duration of life from seed to seed, as it is called. It is evident what this means. Instead of having to wait four or five years after a crossing, before the result could be judged by the flowers, Burbank can make his selection in half the time. This, of course, not only includes saving of time, but also reduces the size of the cultures, and consequently the expenses. Burbank's aim is to make Amaryllis one of the most common ornamental garden plants, which will find its place in parks and private residences, in city gardens as well as near the farmer's humble dwelling. In order to introduce new forms into the stock of Amaryllis, Burbank endeavored to cross them with the related Crinums, and, from what we saw, his first trial was crowned with success. From the Florida swamps he obtained a wild Crinum Americanum, which has proved its fitness for crossing, and at the same time he had in his hothouse varieties from tropical regions, which he was going to cross with more hardy forms, so that they would feel at home in the California climate.
Among all the above mentioned points upon which I desired to draw special attention is the shortening of life from seed to seed. As the experiments, with a few exceptions, are conducted on perennials, and as vegetative propagation only is resorted to for multiplication, it would in many cases necessarily take several years before the plants flowered. Where repeated crossings have to be made this would cause considerable difficulty.
The means which make it possible to shorten the vegetative period are three: first, the splendid climate of California; second, the selection of the earliest flowering seedlings, and, finally, the method of grafting. Experience has taught us that the best way of forcing the stem or branches of seedlings to an early development is by grafting them on older trees. On a good-sized plum tree may be grafted, as said before, hundreds of seedlings. They will bloom in a couple of years, and as soon as they bear fruit selections can be made. The inferior grafts are then removed, so as to allow room for the good ones to develop more rapidly.
In the process of artificial crossing the greatest possible precautions have to be taken in the application of pollen. Yet the method is as simple as possible, because the hybridization is carried on on such a large scale. First the stamens of the flowers to be crossed have to be removed. This is usually done while the flower is in bud and the stamens close together. One circular cut only is sufficient. Care must, of course, be exercised so as not to hurt the pistil. Next protection against insects has to be provided for, as otherwise pollen might be transferred from other flowers and the expected results spoiled. In scientific experiments a great deal of attention is paid to this, and the flowers are carefully enclosed in cases of metal gauze or in especially prepared paper bags, so that no insects can reach them. In practical plant breeding this would, however, be too cumbersome. By the circular cut mentioned not only are the stamens cut through, but the corolla is also removed, and the flowers are consequently not so conspicuous and do not attract the insects, except where there is fragrance. The majority of Burbank's improved fruit trees belong to the first category. In practical work the visit of a single insect is not so much feared, because all the mischief it may do in bringing the pollen is to produce a valueless hybrid. This can later be destroyed. Besides, the insect may come too late to bring about any result. But there is also a possibility that a new and good hybrid may be produced. The application of any cover is, therefore, entirely out of the question. This is the reason why unexpected results of such practical work are never entirely free from the suspicion that they are due to accidental introduction of pollen. Such results, therefore, do not enable one to draw reliable scientific conclusions.
Burbank's method is to collect the pollen required for these crossings on watch-glasses, as it keeps fresh for about a week. With these glasses he goes to the plants he wants to pollinate and applies with his finger tip a little of the pollen on the stigma. This is, as a rule, not yet ripe, but the pollen adheres to it until it matures. Fecundation thus begins at the time the stigma becomes glutinous, which lessens the possibility of other pollen being introduced.
I wish now to consider one of the most remarkable features of Burbank's work, the immense scale upon which it is conducted. This is the best plan for obtaining the most variations in a short time. He starts thousands of seedlings for each hybrid, and when the culture admits and the interest requires it, this number is increased to 50,000 or 60,000. In order to give an idea of the significance of these figures and of the work they imply, Burbank shows in one of his catalogues an autodafé of hybrid raspberries and blackberries. For the purpose of getting a hybrid with larger berries and bigger bunches he cultivated 65,000 seedlings until they blossomed and were in full bearing. A few dozens were selected, and the balance, heavily loaded with fruit, were dug up and gathered in a pile, which was then reduced to ashes. And this goes on every year; fourteen or fifteen such bonfires a year are not uncommon. One consisting of 10,000 to 15,000 roses, luxuriantly flowering seedlings, annihilated the work of a number of years after the selection of only three good varieties. Half a million lily bulbs were entirely destroyed after fifty of the best had been separated for further cultivation. And so I could cite a number of instances.
It is evident that the chance of finding something good is much greater if the selection can be made from hundreds of thousands instead of from a few hundred only. Those who wish to compete with Burbank will have to accept this principle, and if this can not be done, they had better follow a different method and select species that admit the use of different methods.
It is theoretically of great interest to compare Burbank's principle with the methods of selecting generally in vogue in Europe. There the work is not performed on such a large scale. Preference is given to repeated selections, and the idea is prevalent that the desired results can be reached only by following the regular road. The question is whether by such repeated selection we proceed faster than by a single sowing on a larger scale. "We can easily calculate the proportion, and it can be said that with five years' work a hundred times smaller number of plants have to be cultivated. This would, of course, lessen the expenses in proportion, but there is always the disadvantage of the result being available so much later.
When novelties are wanted in varieties of Begonias, Geraniums, Dahlias or Fuchsias, for instance, which annually produce many new forms, the hastening process would be of no value, but in new genera unexpected results are often attained, and in that case the hastening method will amply repay the expense. Yet these questions are the secrets of breeders. Of scientific importance is the question whether repeated selections are alone sufficient to bring about the same end, and further if by this means more variations are produced.
We have no facts which would decide this, and I would not have brought up the question, had it not been for its great influence on the study of evolution. It is closely connected with the question whether species slowly merge into one another or whether they originate by mutations. In the former case small deviations would increase in the course of generations, and thus a long series of intermediate forms would connect the new and the old species. In the latter case a jump is made without any intermediate stages. So long as there were not sufficient instances of this mode of change, and so long as we had to rely upon cultivated varieties only as proof, the first proposition was naturally the most probable. It rested on experience in agriculture and horticulture in regard to improvements of races, and it was believed that species in nature originated in the same manner. The result of breeding on such a large scale as that mentioned above was at the time unknown, and it was believed that the results could be obtained only by repeated selections. If by experiments on a large scale the varieties could be produced at once, the former view would evidently lose much of its value.
The magnitude of Burbank's work excels anything that was ever done before, even by large firms in the course of generations. The number of fruits and flowers which he has improved is unequaled. Others confine themselves to one or two genera; he takes hold of everything. The majority of breeders who became famous by their improvements of certain groups took up this work merely as an adjunct, as a means of widening their commercial relations, thus creating a greater demand for their nursery products. Burbank commenced in the same way, but as soon as he had obtained what he thought he required, the nursery business was abandoned, and he devoted himself exclusively to the improvement of flowers and fruit. It is to this resolution he owes his present fame.
Another point of importance which is also evident from Burbank's work is that in many genera the development of hybrids seems to have reached its limit. In some cases neither Burbank nor any other breeder could produce something new. Apples, pears, peaches, strawberries and a few other types are quite exhausted. The circumference of their form-circle, if I may be allowed to express myself this way, or, as Americans say, their possibilities, are already taken up in cultivation. Inside that circle, of course, improvements are possible, and every one who eats canned apples, or pears, or peaches from California knows that progress in regard to these fruits is evident enough. But Burbank himself considers those species exhausted, and he asks for his improvements no higher rank than what already exists. He has added to them only greater productivity and the qualities required for packing and shipping. It is, however, by just these qualities that a great deal of California's prosperity has been created and the fruit export to Europe increased, qualities which the consumer applauds as much as the European orchardists fear them.
From a scientific point of view Burbank's varieties are but individual, by which I mean that the variety has been produced by one single individual, hence from one seed. That specimen has then been multiplied by vegetative propagation into the thousands, or probably millions, of plants which are in the market. As an individual the variety preserves the characters obtained through hybridizing.
Exceptions to this rule are rare. Burbank has, however, obtained a few hybrids which are stable when raised from seeds. These are naturally crossings of stable species or at least stable hybrids. As an example I may mention the hybrid between the California dewberry and the Siberian raspberry. Both have small and insignificant fruits, while the hybrid on this point greatly surpasses either parent. In Europe we have long known similar instances through the studies of wild hybrids by Kerner, and by Wichura, Janzewsky and many other writers regarding cultivated bastards.
If the relationship between species is not close enough, all attempts to hybridize are frustrated. Either the crossing is a failure, and no seeds are produced, or hybrids are obtained which are infertile. In the case of flowers this is not of so much importance, but in regard to fruit trees such a result is a complete failure. It is evident that nature has here drawn a limit which man can not cross. This boundary line is, however, not marked, and consequently once in a while surprising results are obtained. Hybrids which are infertile in thousands of cases may for once prove a success among hundreds of thousands. Burbank has an example of this in his crossing of Petunia with tobacco. From numberless hybrids he got one germinating from seed. He named this curiosity Nicotunia (from Nicotiana and Petunia). It was not very attractive and succumbed after one year, having flowered profusely, but failed to produce any seed.
It is unfortunate that we can not see this limit of nature in advance, but have to learn it by experience. And this experience includes an almost incomprehensible amount of labor of which no one hears anything.
- ↑ Authorized translation from the Dutch, by Dr. Pehr Olsson-Seffer, Stanford University. This article was written by Dr. H. de Vries, the eminent botanist and originator of the mutation-theory, while in California last summer. It was originally published in the magazine 'de Gids' in Holland, and forms a part of the third chapter of a book 'Naar Californië' by de Vries, which recently appeared in Amsterdam. It is of considerable interest to note the impressions de Vries, the scientific botanical experimenter, received during his first visit to Luther Burbank, the foremost practical plant-breeder in the world, whose remarkable achievements have created world-wide admiration, and to whom the Carnegie Institution recently granted an annual appropriation to insure the undisturbed continuation of his work for the next ten years.
- ↑ The original reads: De kleur berust waarschijnlijk op een verbinding van de kleurstof van somniige soorten met de scheikundige inhoudstoffen van de cellen van andere. Maar voorloopig is dit nog slechts een vermoeden.