How Far Can Plant Improvement Go?
The Crossroads-Where Fact and Theory Seem To Part
"When I first began this work," said Mr. Burbank, "I was taught that a combination between two varieties of the same species was possible-that I might cross one plum with another plum, for example, to get a new variety-but that the species marked the definite boundary within which I might work. The science of that day was firm in its belief that a seed-bearing, self-reproductive cross between plants of different species was beyond the pale of possibility. A little later on, when I succeeded in combining the plum with the apricot, and produced, thereby, a new fruit whose parents were of undeniably different species, the law, or rule, was moved up a peg; and I was told that while it might be possible to effect combinations between different species, yet that must be the limit of accomplishment; that combinations between the next higher divisions, genera, were beyond the power of man to effect. Then, when I was able, after a time, to take parents of two different genera, like the crinum and the amaryllis, or the peach and the almond, or a score of others which might be mentioned, and to effect successful seed-producing combinations between them, I began to hear less and less about laws and rules. The fact is that the laws and the rules are all man-made. Nature, herself, has no hard and fast mode of procedure. She limits herself to no grooves. She travels to no set schedule. She proceeds an inch at a time-or a league-moving forward, always, but into an unmapped, uncharted, trackless future. I like to think of Nature's processes as endlessly flowing streams; streams in which varied strains of heredity are ever pouring down through river beds of environment; streams which, for ages, may keep to their channels, but each of which is apt, at any time, to jump its banks and find a different outlet. Just about the time we decide that one of these streams is fixed and permanent, there is likely to come along a freshet of old heredity, or a shift in new environment; after which we must rebuild our bridges and revise all our maps."
Since the subject of classification is an important one; and since Mr. Burbank upsets some man-made law or theory on an average of about once in every sixty days, it may be well, at this point, to take a bird's-eye glimpse over the maps and charts which have been worked out. With a subject in which the bulk of truth is masked in the obscurity of past ages, and with many men of many minds attacking it from many viewpoints, it is only to be expected that there should be differences of opinion. But, for the sake of making the explanation clear, we may, for the moment, overlook minor divergences and view, only, the main backbone plan which meets with the broadest acceptance. To begin at the beginning, we see, first, spread before us, three kingdoms, whose boundary lines are well surveyed, and whose extent is all-inclusive. These, as our Duffy's second reader told us, are the mineral, the animal, and the vegetable kingdoms. Our interest lies now in the vegetable kingdom, which divides itself into six (perhaps seven) branches, or subkingdoms, called phyla. The lowest of these subkingdoms includes only those vegetables of the simplest type which reproduce by splitting themselves in two. In this subkingdom live the death-dealing bacteria, which bring about such human diseases as tuberculosis and malaria, or such plant diseases as black rot; and the good bacteria, too, which are everywhere, helping us to digest our food, and without whose help the higher subkingdoms of plant life could not exist; and other plants of the same grade. The next subkingdom, higher by a step, includes the yeast which we use to raise our bread, or those microscopic vegetables which turn hop juice into beer, apple juice into cider and rye juice into whisky; and others. Those who prefer to chart seven subkingdoms instead of six, divide this branch into two, making the slime-molds a separate phylum. The next subkingdom, ascending the scale, includes, among others, the mosses and liverworts. From these it is but a step to the next subkingdom, which includes the ferns-the highest type of flowerless plants, and the first, in the ascending scale, to exhibit a complete development of root, stem and leaf. The final subkingdom, and the one into which our work principally takes us, embraces those plants which produce seeds. Taking, then, this latter, the highest subkingdom, we find that it separates into two broad divisions, called classes, one of which is distinguished by bearing its seeds in enclosed packages called ovaries; the other bearing seeds which are exposed, or naked. The first of these classes includes the vast majority of seed-bearing plants; the other including principally those trees, like the pine and the cypress, which bear their seeds in open cones. Next, on our chart, we shall find that the class is subdivided into orders. The order represents a collection of related families. As an example, the order Rosales is made up of the rose family, the bean family, the cassia family, the mimosa family and twelve other families closely allied. Below the order comes the family-a division which is still broadly inclusive; the rose family for example taking in not only the rose, itself, but the apple, the blackberry and sixty-two other plants whose close relationship might not at first be evident. From the family we next narrow down to the genus-which separates the rose from the apple and the blackberry and gives each its own classification. Beneath the genus there comes the species. And beneath the species the variety. We may take it as a safe observation that the simpler the form of life, the less the tendency toward variation; the more complex, the greater the opportunity for individual differences. So, in the simpler subkingdoms, and in the more general divisions down to and including the order, the lines of division are more readily differentiated, and the work of classification has been fairly free from quarrels. But as the order breaks up into families, and the family breaks up into genera, and the genus breaks up into species, and the species breaks up into varieties, and variations tend more and more to carry the individual away from its kind, there are to be found dissentions and differences of opinion which could hardly be chronicled in twelve full volumes of this size.
Nor is this divergent opinion surprising. It is said that, of an iceberg floating in the sea, but one-eighth is visible to the surface observer, while seven-eighths of the mass are submerged beneath the water line. Who, from looking at the one-eighth in view, could be expected to draw an accurate detail picture of the iceberg as a whole? The vegetable kingdom which presents itself to our vision today has been under observation, at most, but a few hundred years. It has behind it, who shall say, how many tens of thousands of generations of ancestry which, coming before man, went by unobserved-yet which, under new environment, are continually bursting forth to confuse us. How can man, with only one ten-thousandth of his subject revealed to him, be expected to make charts or maps which shall withstand onslaught, or be superior to criticism?
For the sake of ready understanding, we may, however, summarize plant life into the broad classifications outlined above. First, the vegetable kingdom, which includes all plants. Second, the subkingdom or phyla, six or seven in number. Third, the class, which ranks above an order and below a phylum. Fourth, the order, which ranks between the class and the family. Fifth, the family, which ranks below an order but above the genus. Sixth, the genus, which ranks below a family but above the species. Seventh, the species, which ranks below a genus and above the variety. Eighth, the variety, which ranks below a species and above the individual. Yet with but one certainty in the entire scheme of classification that certainty being the individual, itself. Men may tell us that a plant belongs to one genus or to another, that it is of this species, or of that or that it is even of a different family than at first we thought-but these, after all, are but theories, built up about the plant by man-theories which serve merely as guide posts in our work. The plant itself, the individual plant, if we but watch it and give it an opportunity to show, will tell us for itself, beyond dispute or denial, just what manner of plant it is-just what we may hope for it to do.
Next in importance to classifying plants, from a superficial standpoint, is a method of naming them. When we go to the florist's we ask for roses, or marigolds; when we go to the fruiterer's we talk to him of oranges, and plums, and cherries; when we go to the green grocer we ask for lettuce, or cabbage, or peas; when we select furniture we talk of it as being made of mahogany, or oak, or walnut. Thus, commonly, we call all forms of plant life by their nicknames-and by their nicknames only do most of us know them. One reason, likely enough, is that the scientific names of plants are in Latin-for the good reason that the Russian, or Swedish, or Spanish, or American scientist is able to describe his work, thus, in a common language. In giving a plant its Latin name, no attention is paid to its class, order or family. The name of the genus becomes its first name. The name of the species follows. And the name of the variety, when given, comes last. Thus, in writing the scientific name for an apricot, or a plum, or a cherry, we should give first the name of the genus, which, for all of these, is Prunus. If we are to describe, for instance, a cherry of the species Avium, we should write, following the name of the genus, the name of the species, as Prunus Avium. And then, if we were to write the name of some particular improvement in that species of cherry which Mr. Burbank had wrought, say the famous Burbank cherry, we should follow the names of the genus and the species with the name of that variety, as Prunus Avium Burbank. Or, if we were to prepare a technical article, about this species, we should write Prunus Avium at the first mention of it, and contract it to P. Avium when mentioning it thereafter. In this work, in order to gain clearness with the least effort, and to avoid confusion through the use of disputed terms, it has been decided, so far as possible, to call plants by their commonest names; going, wherever necessary, into a brief explanation in order to identify the plant clearly in the mind of the reader. Our work is to be a practical work, and the effort which it would cost to master thousands of Latin names might, it is believed, be better expended in a study of the principles and the practice. There arises, unfortunately, a confusion through use of common names. The California poppy, for example, is not a poppy at all; but for the purposes of this work it has been deemed best to call it the California poppy, by which name it is generally known, rather than to refer to it as Eschscholtzia; and so on throughout the list of other plants. No common name is used, however, which is not to be found in the dictionary; so that those whose scientific interest is uppermost have but to refer to their Webster, which gives a greater wealth of detail than could be hoped for in a glossary or an appendix to these volumes.
"A few years after I came to Santa Rosa," said Mr. Burbank as he was sitting on his porch one evening, "I was invited to hear a new minister preach on a subject which, I was assured, would be of interest to me. It was not my own church, so I tried to find my way to an unobtrusive seat in the rear, where I should disturb no one. But, as if by prearrangement, the usher would not have it that way-I was led to the front center, where I was given a pew to myself. As soon as the sermon began, I saw the reason for it all. That preacher, with a zeal in his heart worthy of a better cause, had evidently planned a sermon for my own particular benefit. He was determined to show me the error of my ways. He began by describing 'God's complete arrangements' as evidenced in the plants about us, and rebuked me openly for trying to improve on the creations of Omnipotence. He held me to ridicule as one who believed he could improve perfection; he predicted dire punishment for attempting to thwart Nature and tried to persuade me, before that audience, to leave God's plants alone. Poor man! Whatever may have been thought of his good taste, or his tact, or his judgment, I could hardly take offense at his sentiments-for they really reflected the thought of that day. Poor man! He could not see that our plants are what they are because they have grown up with the birds, and the bees, and the winds to help them; and that now, after all these centuries of uphill struggle, man has been given to them as a partner to free them from weakness and open new doors of opportunity. He could not see that all of us, the birds, and the bees, and the flowers, and we, ourselves, are a part of the same onward-moving procession, each helping the other to better things; nor could many of the others of his time see that. And the botanists of that day, less than four short decades ago, found their chief work in the study and classification of dried and shriveled plant mummies, whose souls had fled-rather than in the living, breathing forms, anxious to reveal their life histories. They counted the stamens of a dried flower without looking at the causes for those stamens; they measured and surveyed the length and breadth of truth with never a thought of its depth-they charted its surface, as if never realizing that it was a thing of three dimensions. And that is why those who had devoted their lifetimes to counting stamens and classifying shapes told me, through their writings, that a cross might be made within species, but never between species; that is why when I did make a cross between species they looked no further into the truth, but simply moved up a notch, and said, 'Very well, but you cannot make a cross between genera'; that is why, when I did that very thing, not once, but scores of times, that type of scientist lost interest in rule making and went back to stamen counting."
To realize the point more clearly, let us observe for a moment the common tomato-which belongs to that large division of plants, the nightshade family. Just as the rose family includes not only the rose, but the apple and the blackberry and sixty-two other plants, so the nightshade family includes seventy-five genera and more than eighteen hundred species. The classification is built around structural facts, such as that plants of this family originally had alternate leaves with five stamens and a two-celled ovary, or egg chamber, each cell containing many eggs. These structural similarities in the plants of this family trace back to a common parentage and fully justify the classification of these seventy-five genera in a single family. If we were to look not at the structure, however, but at the seventy-five plants themselves, then, and only then, could we fully realize the wonders which environment, toying with that common heredity within the plant, has wrought. We should see, among the seventy-five brothers and sisters of that family if they were spread before us, the poisonous bitter-sweet, and the humble but indispensable potato; the eggplant and the Jerusalem cherry; the horse nettle and the jimson weed; the tobacco plant and the beautiful petunia; and the tomato itself. We should see seventy-five plants with original structural similarities, yet differing, in every other way, as night differs from day; and we should be able to trace, if we observed closely enough, the points at which, in the history of this family, new environment, oft repeated, has hardened into heredity, subject to the call of still newer environment, which has not been lacking to bring it out; we should be able to trace out, by easy stages, why one branch ran to the poisonous bitter-sweet, another to the potato with its food product below the ground, another to the tomato with its tempting fruit displayed on vines above; another to tobacco, valued for its chemical content-and so on throughout all of the variations. The tomato, we should see, was the last of the family to fall into a violent change of environment. A tropical plant, bearing fruits about the size of a hickory nut and not believed to be edible, the tomato found its way into the United States within the past century. At first, the tomato plant was prized merely as an ornament; it was grown as we now grow rose bushes, and the fruit was looked upon as a mantel decoration, until, by accident, it was discovered to be edible. There are, in fact, many such ornamentals today which might bear us edible fruit. One, in particular, the passion flower, which Mr. Burbank is developing, will form the subject of an interesting description later on. Following the discovery that the tomato was edible came the same course of unconscious selection that falls to the lot of every useful plant. The biggest tomatoes were saved, the better tomatoes were cultivated. In the environment of the tropics, the tomato fruit of hickory nut size was ideal; it cost less effort to produce than a larger tomato; it contained sufficient seeds to insure reproduction. But with the advent of man into its environment, its seed chambers increased in number, the meat surrounding the seeds increased in quantity and improved in quality; so that in virtually half a century the large, luscious, juicy tomato we now know is universally to be found in our markets, in season and out. No man can say how many thousands or tens of thousands of years it took wild environment to separate the tomato from the seventy-four others of its family. Yet, in less than half a century, see what changes man, as an element of environment, has worked! We take the seeds of our Ponderosa tomatoes and set them out in a can or a shallow box, and midsummer brings us new Ponderosas-so well have we succeeded in fixing the traits we desire. But were we to take those same seeds to the tropics and plant them under the conditions of only fifty years ago an entirely different thing would happen. The first generation would be Ponderosas, more or less like those we grow here. But in the second generation, or, at latest, the third, the seeds of those very Ponderosas, when planted, would grow into vines which bear the old type of tomato-the size of a hickory nut-an immediate response, almost, to the wild tropical environment which prevailed before man came along. From the botanists of only a century ago, examining only dead tomato blossoms from the tropics, and dried tomato fruits the size of hickory nuts-how could we expect an inkling, even, of what the tomato with less than half a century of cultivation could become? How short, indeed, the time which environment requires to transform a plant beyond recognition-especially when man, either consciously or unconsciously, becomes a part of that environment! And, knowing what the Chinese did to the pear, what the American Indian did to corn, what our own fathers and mothers did to the tomato, can we not see that, while stamen counting has its place, yet, for real achievements in plant improvement, we must look for help not so much to the stamen counters as to the plants themselves as new environment brings their old heredities into view.
Mr. Burbank has made combinations between species; he has made combinations between genera, not once, but many times; fertile, seed-bearing combinations. How far, then, can plant combination be carried? Is it possible to go above the genus and make combinations between families? Or to go above the family and make combinations between the orders? Or to go above the orders and make combinations between the classes? Or to go above the classes and make combinations between the subkingdoms? "Give us time," says Mr. Burbank, "and we could accomplish anything. The limitations of our work are not limitations,imposed by Nature; they are limitations imposed, alone, by the clock and the calendar. Here we are, fighting ten thousand years of hardened heredity with five or ten years of new environment; sometimes we succeed; it is no wonder that more often we fail; in five years, however, we can usually work a transformation; if we could afford to spend fifty years on a single plant, we could upset every rule that has ever been formulated about that plant; and if we could spend five thousand years, we could, simply by guiding Nature, accomplish, well, anything. Every season we are working changes which Nature would take ages to work; but from a practical standpoint we must seek always to take advantage of the old heredities which Nature has stored up-to make them serve our ends, because this can be done quickly; rather than to create and fix new heredities which might take so long as to rob our work of its usefulness."
Here, then, is Mr. Burbank's bird's-eye view: Before us is a world of living, onward-marching plants-plants which have made, are making, and will continue to make, their own rules as they go along. Here, before us, too, is the propaganda of our subject with its maps, plans, charts, rules, laws, theories, beliefs, built up too fixedly, too arbitrarily, too superficially, perhaps, but very completely, nevertheless, around this onward-marching mass. Let us use to the utmost all the help that science can give; to save time, let us accept the laws and the rules, let us have confidence in the maps and the charts, until the plants themselves show our error. Let us search, always, for stored up heredities to convert to our use, just as we would seek stored up diamonds, or gold, or coal, instead of trying, by chemistry, to produce them. Let us realize, always, that everything is possible with time; but let us seek out all the short-cuts we can. For, after all, we have so little of Time!
With time as our limiting factor, then, we shall find, in plant work, many things which we cannot hope to accomplish. We shall find plants, of course, of different species, and different genera-a surprising number, in spite of the old belief, which will combine readily to produce fertile offspring constituting a new species or a new genus. We shall find plants of different species or genera which combine to make a sterile offspring-a mule among plants. And we shall find plants which can hardly be combined at all-plants in which the pollen of one seems to act as a definite poison on the other-plants with large pollen grains which cannot push their tubes down the pistils of smaller flowers-and plants which, through long fixed heredity, seem as averse to combination as oil seems averse to combining with water. "But no man," says Mr. Burbank, who has just read this, "can tell until he has tried-tried not once, but thousands and thousands of times."
"What is that?" asked a seedsman who was visiting Mr. Burbank. "That is a Nicotunia," replied Mr. Burbank, "and you are the first man in the world who has ever seen one. It is the name which I have given to a new race of plants produced by crossing the large flowering nicotianas, or tobacco plants, with petunias. It is, as you can see, a cross between two genera of the nightshade family."' "H'm!" said the seedsman. "You know the secret now," said Mr. Burbank, "but if you think that you can produce these nicotunias as you would hybrid petunias, or crossbred primroses, go ahead and try; there is no patent on their manufacture; but if the five hundredth cross succeeds, or even the five thousandth, under the best conditions obtainable, you will surely be very successful. I do not fear any immediate competition. This one cost me ten thousand tries." Perhaps those who have said that species could not be combined with species, or genus with genus have tried only once or twice or a dozen times. Perhaps Mr. Burbank's patience and persistence account for some of the upset laws.
"Why not content ourselves to work within varieties as the bees work?" asks some one. "Because by going out of the varieties and combining between species, and going out of the species and combining between genera, we multiply almost infinitely the combinations of old heredities which we may bring into play-we lessen the work which we have to make environment do by spreading before us more combinations of heredity-we accomplish in two years what otherwise might take two lifetimes. In all, Mr. Burbank has made one hundred and seventy-nine combinations between different species and different genera, treated elsewhere, all of which were thought to be impossible. It was such combinations as these which enabled him to perfect the cactus, to produce the plumcot, to make the Shasta daisy-in fact, it was Luther Burbank's lack of respect for man-made laws, when plants told him a different story, that has given the world eighty percent of his productions-that has led him to ninety percent of his discoveries in practical method. "The only reason," said Mr. Burbank, "that we do not combine between families, and between orders, and classes, is that we haven't the time."
So we see that the science of plant life is not an exact science, like mathematics, in which two and two always equal four. It is not a science in which the definite answers to specific problems can be found in the back of any book. It is a science which involves endless experimenting-endless seeking after better and better results. Theories are good, because, if we do not permit them to mislead us, they may save us time; laws, and maps, and charts, and diagrams-systems of classification and of nomenclature-all these are good, because, if they are faulty, they still reveal to us the viewpoint of someone who, with diligence, has devoted himself to a single phase, at least, of a complex subject. But we must remember that the theories, most of them, are built around dead plants. While the facts we are to use are to be gathered from living ones. So, every once in a while, when we come to a crossroads where that kind of theory and this kind of fact seem to part, let us stick to the thing which the living plant tells us, and assume that evolution, or improvement, or progress, or whatever we choose to call it, has stolen another lap on the plant historians. And let us remember that the fact that ours is not an exact science, with fixed answers to its problems, is more than made up for by the compensating fact that there seems to be no limit to the perfection to which plant achievements may be carried-no impassable barrier, apparently (save time-which limits us all, in everything), beyond which our experiments may not go.
-Nature did not make the laws; she limits herself to no grooves; she travels to no set schedule.
This text is from: Luther Burbank: his methods and discoveries and their practical application. Volume 1 Chapter 7