The potentialities of every plant and its limitations are inherent, fixed and immutable in the seed from which it is developed and are made up of the balanced sum of the different tendencies it receives in varying degree from each of its ancestors back for an indefinite number of generations. A very slight difference in the character or the degree of any one of the tendencies which go to make up this sum may make a most material difference in the balance and so in the resulting character of the plant produced. Different plants, even of the same ancestry, vary greatly in prepotency or in the relative dominance of the influence they have over descendants raised from seed produced by them.
In some cases all the plants raised from seed produced by a certain plant will be essentially alike and closely resemble the seed-bearing plant, while seed from another plant of the same parentage will develop into plants differing from each other and seemingly more influenced by some distant ancestor or by varying combinations of such influences than of those of the plant which actually produced the seed from which they were developed. Successful seed breeding can only be accomplished by taking advantage of these principles of heredity and variation, and by a wise use of them it is possible to produce seed which can be depended upon to produce plants of any type possible to the species.
The first essential for breeding is to have a clear and exact conception of precisely what, in all respects, the type shall be and then the securing of seed which has come from plants of that exact character for the greatest possible number of generations, carefully avoiding the introduction by cross-pollination of tendencies from plants differing in any degree from the desired type. Secondly, seed should be used from plants which have been proven to produce seed, which will develop into plants like themselves or are strongly prepotent. A practical way to accomplish this in the tomato is as follows:
By experiment and observation form a very clear conception of precisely the type of plant and fruits which is best suited to your needs. This may be done by the study of available descriptions of sorts, by conference with those who have had experience in your own or similar climatic and soil conditions and in raising fruit for the same purposes and, best of all, by trials of samples of different sorts and stocks on your own grounds. Having formed such a conception, write out the clearest possible description of exactly what you want and the ideal plant you are aiming at, stating as fully and minutely as possible every desirable quality and also those to be avoided. I consider not only the formation of an exact ideal, but the writing out of a most minute and exact description of precisely what in every particular the ideal plant should be and the rigid adherence to that exact ideal in selection, as the most important elements of successful seed breeding. Without it one is certain to vary from year to year in the type selected and in just so far as he does this, even if it be toward what might be called improvements or in regard to an unimportant quality, he undermines all his work and makes it impossible to establish a strain which can be relied upon to produce an exact type.
With this description in hand, search out one or more plants which seem the nearest to the ideal. In doing this it should be kept in mind that the character of the seed is determined by the plant rather than by the individual fruit. Therefore, a plant whose fruit is most uniformly of the desired type should be chosen over one having a small proportion of its fruits of very perfect type, the others being different and variable. Save seed from one or more fruits from each of the selected plants, keeping that from each fruit, or at least each plant, separate. Give it a number and make a record of how nearly, in each particular, the plant and fruit of each number come to the desired ideal. I regard the saving of each lot separately and recording its characters as very important, even when all have been selected to and come equally close to precisely the same ideal. Quite often the seed of one plant will produce plants precisely like it, while that of another, equal or superior, will produce plants of which no two are alike and none like that which produced the seed, so that often the mixing of seed from different plants of the same general type, and seemingly of equal quality, prevents the establishment of a uniform type.
The next year from 10 to 100 plants raised from each lot are set in blocks and labeled. As they develop the blocks are studied and compared with the original description of the desired type and that of each plant from which seed was saved, and the block selected in which all the plants come the nearest to the desired type, and which show the least variation. From it plants are selected in the same way and to the same type as the previous year. It is better to make selections from such a block than to take the most superior plants from all of the blocks, or from one which produced but one or but a few superlative ones, the rest being variable.
It is also well to consider the relative importance of different qualities in connection with the degree to which the different lots approach the ideal in these respects. Such a course of selection intelligently and carefully carried out will give, in from three to five years, strains of seed greatly superior and better adapted to one's own conditions than any which it is possible to purchase. A single or but a very few selections may be made each year, and the superior value of the seed of the remainder of the seed blocks for use in the field will be far more than the cost of the whole work.
Growing and saving commercial seed.—The ideal way is for the seedsman to grow and select seed as described above and give this stock seed to farmers who plant in fields and cultivate it, much as is recommended for canning, and save seed from the entire crop, the pulp being thrown away. Only a few pickings are necessary and the seed is separated by machines worked by horse power at small cost, often not exceeding 10 cents a pound. They secure from 75 to 250 pounds per acre, according to the variety and crop, and the seedsmen pay them 40 cents to $1 a pound for it. Some of our more careful seedsmen produce all the seed they use in this way; others buy of professional seed growers, who use more or less carefully grown stock seed. In other cases when the fruit is fully ripe it is gathered, and the seeds, pulp and skins, are separated by machinery; the seed is sold to seedsmen, the pulp made into catsup, and only the skins are thrown away. Still others get their supply by washing out and saving the seed from the waste of canneries. Such seed is just as good as seed saved from the same grade of tomatoes in any other way, but the fruit used by the canneries is, usually, a mixture of different crops and grades, and even of different varieties, and consequently the seed is mixed and entirely lacking in uniformity and distinctness of type.
Generally from 5 to 20 per cent. of the plants produced by seed as commonly grown either by the farmer himself or the seedsmen, though they may be alike in more conspicuous characteristics, will show varietal differences of such importance as to affect more or less materially the value of the plant for the conditions and the purposes for which it is grown. In a book like this it is useless to attempt to give long varietal descriptions even of the sorts commonly listed by seedsmen, since such descriptions would be more a statement of what the writer thought seed of that variety should be rather than of what one would be likely to receive under that name.