Cook — Hybrids and }rutalions. 87 



the vegetative vigor of" liybrids is the same phenomenon as the 

 vigor of more normal crosses in spite of their rei)roductive de- 

 cline. 



KINETIC INTERPRETATION OK VIGOR. 



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

 oi»inion 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 (pies- 

 tion from another standpoint and perceive that the additional 

 vigor may be interpreted in both cases as a phenomenon attend- 

 ing vital motion. Evolutional'}' 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 the}' have moved into new positions in the field of de- 

 velopment. Variation and cross-fertilization serve the same 

 puri)Ose, 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 simi)le inertia, but, like 

 bicycles and gyroscopes, maintain 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 

 knoAvn 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. 



