Luther Burbank: Methods and Discoveries pp. 101-121 (1914)

THE TOMATO—
AND AN INTERESTING EXPERIMENT

A VISITING scientist who had seen my little preserving tomato and had learned its origin was curious to know just how I came to make the hybridizing experiment that resulted in its production.

I found it difficult to answer the inquiry to his entire satisfaction. One does not recall all the details as to methods, let alone motives, after an interval of twenty-five years. But so far as can be recalled, I had no very definite object in combining the common tomato and the currant tomato except the one of general interest in the processes of nature, and a sort of all-inclusive desire to see what would happen when plants of such diverse character were united.

My visitor felt that I must have had some definite idea in mind—some ideal tomato at the production of which I was aiming, and he seemed to feel distinctly dissatisfied when assured that in this particular case a result had been achieved that had not been forecast. The plant developer had been like a chemist putting together newly discovered elements. He knew that he would probably get something interesting, but just what that something was to be could not be predetermined.

TWO TYPES OF INVENTIONS

I recall this incident by way of illustrating another phase of the plant developer's art than that illustrated by the development of the canning pea as detailed in the preceding chapter. In that case, it will be recalled, the plant developer was in the position of an inventor called upon to meet a precise set of specifications. He knew from the outset what was to be aimed at and, having acquired a certain craftsmanship, he knew how to set about securing it.

A large number of inventions in the mechanical world have such an origin as this.

When Edison started out to find a filament that would show just the right resistance to the electric current, and yet would not be consumed with its own heat, he knew just what he was seeking, and his problem of the development of an incandescent light bulb was comparable, in a general way, to the problem of producing a canning pea of just the right size and quality.

But, on the other hand, a long list might be cited of inventions and discoveries of vast importance that were matters of accident. Perkins' discovery of the aniline dye; Nobel's discovery of nitro-glycerine; Röntgen's discovery of the X-ray; Becquerel's discovery of radio activity—these are instances where a man found something for which he was not specifically looking. Of course he had to be in line of discovery. It was essential that he should be handling the right materials, and working in a laboratory having the right accessories, or the discovery could not have been made. Nevertheless, in each case, the discoverer found something for which he was not seeking; his experiment had results that he could not have predetermined.

And here again, the analogy with that other type of experimentation through which, for example, the preserving tomato was developed will be obvious.

LOOKING FOR SURPRISES

The point to be emphasized is that the plant developer is an inventor who works sometimes according to one method and sometimes according to another. He is dealing always with complex and intricate matters. Sometimes he has studied them so well that he knows what to expect of them in certain combinations. In other cases he is feeling his way, and has no very clear notion of what to expect.

It might be said that he is looking for surprises rather than for anything definite; and in that event he is pretty sure to find what he is looking for.

Such at least was my experience in the early experiments with the tomato that led ultimately to the production of the particular hybrid at the moment under discussion. These experiments had their origin at the very beginning of the period of my investigations in the field of plant development, a good while before I came to California.

But in those days, notwithstanding one or two successes, I was only laying the foundation for my future work--learning how to handle the tools of my trade. So although there may have been interesting discoveries within reach, I did not always know how to grasp them.

I had not learned, for example, the all-important lesson that the second-generation hybrid, rather than that of the first generation, is the one that must be looked to, in a large number of cases, for important development.

THE STORY OF A FRUIT-LIKE TOMATO

But when I came to California and found opportunity for expanding the work, I from time to time took up the old New England experiments where they had been left.

In some cases I had brought seeds with me, and was able to complete under the new conditions experiments that had been begun in New England. In other cases it was necessary to start anew, but I had experience as a guide, and that constituted an asset that often proved a wonderful time saver.

In the case of the tomato, experimentation was reopened on a comprehensive scale about the year 1887. It was at this time that I hybridized the common tomato and the currant tomato and produced the interesting new form about which we have just spoken. The common tomato needs no description, but the currant tomato is much less familiarly known. It is a plant with long, slender, trailing vines and slender leaves and it bears racemes of small currant-like fruit. It occurred to me that it would be highly interesting to hybridize this trailing plant with a particularly tall, upright, compact variety of the common tomato.

The cross was made reciprocally, pollen from each plant being used to fertilize the stigma of the other.

The fertilization was effected without difficulty, and an abundant supply of seed was produced. The hybrids that grew in the next generation were many of them pretty clearly intermediate in form and appearance between the parents. But some of them were almost ludicrous in appearance. They took on twisted and contorted forms, and in particular their leaves were curled and twisted into fantastic shapes.

As to fruit, some of the plants produced long clusters with tomatoes much larger than cherries; others furnished small fruit like that of one of the parents. And in some cases a plant that had retained the short stocky tree form of the common tomato bore clusters of small tomatoes in bunches similar to those of the other parent.

The foliage varied astonishingly between the two types. In some there was an exact compromise that was very curious. The dark, blistered leaves of the ordinary tomato, combined with the long, slender leaves of the currant tomato, produced a most interesting effect. Other specimens showed every possible gradation between the parent forms.

Here, then, was a case in which there was no conspicuous dominance of one parent or the other as regards any individual character that could be segregated and classified.

Neither as to size and form of plant-stalk, nor as to leaf, nor as to the fruit itself, was there clear prepotency or dominance of one parent over the other.

If there was an exception to this it was perhaps that the fruit tended to be borne in clusters, as in the case of the currant tomato, rather than singly or in small groups as with the ordinary tomato.

Attention is called to these diversities because it is well to emphasize anew that the phenomena of the clear segregation of "unit" characters, with the exhibition of dominance and recessiveness which the pea with which Mendel experimented manifests so beautifully, and which we have seen manifested in the characteristics of numerous other plants-is not a universal phenomenon that the plant experimenter may confidently expect always to discover and use as an easy and simple guide along the path of plant development. Different species of plants, different varieties, even different individuals show diversity as to the extent to which the so-called unit characters are segregated and mutually combined or antagonized, as the reader who has followed the story of various plant developments already outlined is clearly aware.

We shall have occasion to revert to this subject more than once, and to point out various possible interpretations of the phenomena, various underlying harmonies that do not appear on the surface. But for the moment we are concerned with the story of the new tomato, and may be content to put forward the facts regarding it without great insistance on their theoretical interpretation.

Suffice it that the progeny of the tree-like tomato and the trailing one were a varied company, giving the plant developer almost endless opportunities for selection.

I chose, naturally, from among them those that bore the handsomest and largest fruit, and in planting these, was enabled, in the course of several generations, to secure a very handsome plant with attractive fruit of new type which came true from seed. It required about six years to produce and make sure of the new variety, which was announced in my first catalog of new plants, issued in 1893. The description there given of the new fruit was as follows:

AN INTERESTING HYBRID

"This distinct novelty and ornamental fruiting plant grows about twelve inches high by fifteen inches across.

"The curious plated, twisted, and blistered, but handsome leaves, sturdy, compact growth, and odd clusters of fruit will make it a favorite ornamental plant."

Another account supplemented this by describing the fruit as "a small, round, scarlet tomato, borne in clusters, the individual fruits measuring only three quarters of an inch in diameter; of splendid scarlet coloring and unusually rich, sweet flavor."

The comparatively rapid development of this curious form of plant, so widely divergent from the ordinary tomato, illustrates the possibilities and suggests the compelling interest of such experiments in hybridizing and selecting even our commonest garden plants.

The work is of course no different in principle from that followed by the plant developer in the orchard, whose work has been detailed in earlier volumes. But there is this important practical difference: In experimenting with such a plant as the tomato, we get results quickly because the plant grows and fruits in a single season. The results of any given experiment may be known within a few months of the time when the seed is planted. This is quite different from the case of the orchard trees, which require, as we have seen, long periods of patient waiting, few of them bearing, even under forced methods of grafting, in less than two or three years, and some of them, such as the pear and fig, requiring a much longer period.

On the other hand, there is one regard in which the orchardist has an advantage. It is not necessary for him to fix his new varieties so that they will come true from the seed, inasmuch as his plants will propagate by division. But in dealing with plants of annual growth, like the tomato, it is obvious that a new variety can have little value unless it will come true from the seed. (The tomato is really a perennial, that is treated as an annual.)

So the task is not completed when a new variety is produced; additional experiments must be conducted to fix the variety. Even this may he accomplished, however, by careful attention to selection, in the course of a few years, as we have just seen illustrated in the case of the hybrid tomato.