266 COOK 



uniformity, progeny so unlike their parents that Dr. White 

 described and named them as a new species. 1 



A third result sometimes reached by transferring plants to 

 new conditions is to induce a more or less general outbreak of 

 miscellaneous variations of an abruptly mutative character. In 

 such instances the stimulation effect may be lacking or very 

 inconstant. Some individuals may be several times as large as 

 their parents, while others are as much smaller. 



Although the new conditions evidently induce the mutative 

 variations, they can not be said to cause them, in any definite 

 evolutionary sense, as proved by the great diversity of the muta- 

 tions which the same change of conditions may call forth. The 

 unfavorable conditions unbalance the organisms, but the indi- 

 vidual lapses from normal heredity take many different direc- 

 tions, without reference to particular requirements of the 

 environment. 



The practical significance of the new-place-effects is, there- 

 fore, entirely different in different instances. As long as the 

 result is an increase of vigor and fertility, the phenomenon is a 

 useful one ; but if the stimulation be so great as to change the 

 characters of the plants and render them infertile the crop may 

 be ruined, and this misfortune may also be reached when many 

 miscellaneous variations and degenerations appear. 



DIFFERENCES ARISING FROM PARTIAL ISOLATION (PORRISM). 



Members of the same species are often more or less unlike in 

 the different parts of their geographical range of distribution. 

 Some of these differences will be found to have relations to 

 differences of environment, but others will persist even when 

 brought into tne same conditions. These geographical diversi- 

 ties represent, no doubt, the results of partial isolation, and are 

 of the same nature as the differences between species. If inter- 

 breeding were adequate, evolutionary progress would be kept 

 uniform over the whole species, but if the organism is sedentary 

 or lacking in facilities of dispersion local diversities may accu- 

 mulate. 



1 White, C. A., 1905. The Mutations of Lycopersicum, Popular Science 

 Monthly, 47 : 151. 



