Page:Popular Science Monthly Volume 62.djvu/285

Rh It is very probable that marry supposed new characters are merely the peculiar result of the blending of opposite characters, neither of which 'dominates' the other; or it may be that the blending of two unrelated dominant characters gives rise to new characters. As an instance of how this might occur, the presence of two chemical substances, one derived from each parent, might give new flavors in fruit, or new colors in flowers. Bateson has demonstrated a case of the latter and shown that the new and radically different color is not a new character at all, but a blending of parent characters which obey Mendel's law perfectly.

Is it not possible that Mendel has also shown to us an explanation of bud sports? These sports are notoriously common on plants known to be hybrids. May not the separation of parent characters occasionally occur at stages of growth other than the formation of germ cells? If such is the case, bud sports at once come under the law.

It does not seem improbable that, once in a while, the parent characters might fail to separate in the usual manner on the formation of germ cells, so that we might have a few cells inheriting both of a pair of opposite characters, and this might extend over a series of generations before the separation finally occurred. Under such conditions, a recessive character might be carried over any number of generations without showing itself, finally cropping out and giving a case of atavism. Perhaps this is the explanation of atavism. It would be interesting in this connection to know if atavic characters are ordinarily recessive.

It is clear that we have before us a working hypothesis that offers a possible explanation of a large number of phenomena heretofore absolutely inexplicable. It will require time to test the hypothesis, even in the limited number of cases suggested above.

The only data thus far published in this country that may be used as a direct test of Mendel's theory are those I secured from hybrid wheats. At the time these data were arranged for publication similar work in Europe was unknown in this country; they were merely arranged to show that similarly bred hybrids split up into the same types, each type tending to occur in a definite proportion. In all my hybrids characters were present that apparently separated in a manner different from that called for by Mendel's theory. Fortunately, however, the data referred to may easily be arranged to test the applicability of this theory to two characters, namely, beards and velvet chaff. In five out of fourteen crosses one parent was bearded and the other smooth, two of the five being reciprocals. Beards being recessive, theory would call for 25 per cent, of bearded plants