Cook Hybrids and Mutations. 87 



the vegetative vigor of hybrids is the same phenomenon as the 

 vigor of more normal crosses in spite of their reproductive de 

 cline. 



KINETIC INTERPRETATION OF VIGOR. 



It is not possible, however, to content ourselves with this 

 opinion as complete and final, because it does not take into ac 

 count the vegetative vigor of mutations, or variations here sup 

 posed to be induced by inbreeding, which has been thought to 

 weaken the vegetative as well as the reproductive energies of 

 the organism. Viewed from the standpoint of some of the cur 

 rent theories of evolution, the association of the vegetative vigor 

 of mutations with that of normal crosses and hybrids is certainly 

 not obvious, but the difficulty disappears if we view the ques 

 tion from another standpoint and perceive that the additional 

 vigor may be interpreted in both cases as a phenomenon attend 

 ing vital motion. Evolutionary progress is accomplished both by 

 new variations and by the combination of those already exist 

 ing.* Normal crosses and abnormal hybrids and mutations may 

 both be thought of as more vigorous than uniform inbred stocks 

 because they have moved into new positions in the field of de 

 velopment. Variation and cross-fertilization serve the same 

 purpose, and under normal conditions of interbreeding both re 

 sult in increased vigor and prepotency. The important evolu 

 tionary function of cross-fertilization is the mutual communica 

 tion of variations. Continued variation, change, and diversity 

 are the general tendencies, not uniformity and stability of char 

 acters. Organisms are not subject to simple inertia, but, like 

 bicycles and gyroscopes, main tain their equilibrium only when 

 in motion. 



Plants often receive an increased impetus of growth by re 

 moval to new soils, or by changes of the constituents of the soils 

 through what are significantly called " fertilizers." It is also 

 known that they sometimes respond notably to the presence of 

 small quantities of minerals not used by them, or even to those 

 directly injurious, just as arsenic, prussic acid, and other active 

 poisons serve in medicine as tonics. As a result of a similar 

 stimulation of growth by mineral salts applied to the eggs of 

 some of the lower animals, Professor Jacques Loeb was able to 



*" Stages of Vital Motion," Popular Science Monthly, 63: 14, 1903. 



