Page:Popular Science Monthly Volume 78.djvu/556

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zoologist, though less acquainted than might be wished with commercial breeding.

Another paper was entitled, "Mendel's Law in Relation to Animal Breeding," and a third, "Heredity in the Light of Recent Investigations."

In the 1907 session of the same body, Mr. Spillman, of the Department of Agriculture, in a paper entitled, "The Chromosome in the Transmission of Hereditary Characters," said: "I believe that it will finally be possible to work out the complete relation so that we can get a full understanding of the behavior of hereditary characters and thus breed for improved forms with almost as much certainty as the chemist mixes solutions in order to produce a desired compound." At the same time and place. Dr. Davenport, of the Carnegie Institution of Washington, used these words: "Indeed, the fact that the enzymes of the germ cells, and particularly of the egg, determine hereditary characters, points the way to the modification of hereditary qualities and to the production of this or that character at will."

The expectations of such sanguine persons have not been realized. Considerable progress has been made, but it has been and bids fair to be more in the nature of a steady march than of a sudden flight.

Those who were most hopeful of the sufficiency of Mendelism overlooked three things: that we are not able to originate any specific character desired; that not all characters are transmitted in accordance with the Mendelian formula; and that, except for purposes of research, it is seldom practicable to breed for but one single or unit character at a time. Approved animal form embraces probably innumerable unit characters. So far, the only definitely known Mendelian unit characters in large animals are superficial ones, such as coat characters, which are of no direct commercial importance. The relation of the vital body characters is not understood and no capacity for useful functions has been shown to be a unit character. Even with the low number of three or four useful unit characters known to be Mendelian, the chance of their being combined in a single individual is so small as to be of no interest to a practical breeder.

The difficulties of perpetuating a character according to Mendel's law are much less serious with plants than with animals. Knowing that there is strong probability of a unit character of a plant's being Mendelian, the certainty regarding the rate at which it may be propagated adds greatly to the attractiveness of plant breeding and greatly stimulates the search for and endeavor to produce valuable variations.

The Breeders and Mendel's Law

Mendelism has, therefore, given considerable immediate aid to economic plant breeding. It has served to interest seed growers in biology