Page:Popular Science Monthly Volume 63.djvu/26

22 of closely related individuals, as distinguished from fertilization by the pollen of the same flower, and since domestication implies inbreeding the habit of self-fertilization would involve no additional injury, but would have an important practical advantage in greatly increasing the chances of pollination and seed-production.

The recognition of symbasis, or the necessity of a broad foundation to sustain the organic structure, permits the inference that some hybrids are sterile and variable for the same reason that closely inbred plants and animals decline in fertility and produce mutations or deviations from the normal type. A hybrid is a mixture or cross between individuals which would not be expected to mix in nature. Among domesticated plants hybridization signifies the reverse of selection, the crossing of varieties which the breeder commonly strives to keep separate. Generalizations to the effect that hybrids as a whole are sterile, variable, weak or vigorous are fallacious, since the results of the crossing depend upon the evolutionary status of the parents. By segregation or inbreeding normal or progressive variation gradually gives place to uniformity and then to mutation, but hybrids between distant types pass at once from the progressive stage to the catalytic. On the other hand, crosses between inbred or closely segregated stocks may show increased vigor and stability, and thus reverse the process of decline. Hybrids, therefore, may be either prostholytic or catalytic as they tend upward or downward in the evolutionary series.

Cross-breeding and close-breeding have the same limits of sterility; and between each and the mean of normal evolution there is, as shown by the experiments of Mendel, Garton, De Vries and others, a region of the relatively infertile abrupt variations variously termed sports,