The Factors of Evolution 245 



and disuse and consequently have no bearing whatever on 

 the question at issue. Whoever heard, for example, of a 

 horse with a docked tail ceasing to use the stump just as vig- 

 orously in fly time, as though possessed of the complete mem- 

 ber ? What was there in the mutilations of Weismann 's mice 

 to prevent the use of the muscles at the base of the tail ? With 

 the bound foot of the Chinese woman this objection would not 

 apply, because the muscles of the foot are intrinsic to the foot 

 itself ; but in this case we have to consider the influence of the 

 father as well as the mother upon the children, and the prac- 

 tise of foot binding in China has been limited to the female 

 sex. 



Are there then no environmental influences which are trans- 

 mitted from parent to child? Is environment a negligible 

 factor in evolution? On the contrary it is undoubtedly the 

 most potent factor, either indirectly in the preservation of 

 those variations (however caused) best fitted to survive, or 

 directly in the induction of variation itself. 



The seed of a flowering plant is the plant itself in minia- 

 ture, containing more or less "endosperm" or nourishment 

 for the growing seedling, until it is able to take root, unfold 

 its leaves and obtain its own sustenance from the soil and air. 

 If the chemical environment of the developing plant (tne 

 young ovule) be modified, what effect will this have on the 

 adult plant? This question led MacDougal, director of the 

 Desert Botanical Laboratory of the Carnegie Institution, to 

 inject various solutions of zinc, calcium, iodine, etc., into 

 the ovaries of many species of plants, with the result that the 

 ovaries so treated produced seeds from which developed 

 plants showing many modifications in form of leaves and 

 flowers and markings of the latter, as well as in the form of 

 the plant as a whole, and some, at least, of these variations 

 have persisted through several subsequent generations. 



The common potato bug has in part redeemed its shady 

 reputation, by materially aiding us in our search for the ulti- 

 mate factor of evolution, namely, the origin of variation. 

 This beetle was originally an inhabitant of Mexico. Feeding 

 upon the night-shade, it followed its food plant northward, 

 and the early settlers found it established on the eastern 

 slope of the Rocky Mountains. The spread of its food plant 

 is attributed by Professor Tower, who has made an exhaustive 

 study of the beetle and its habits, to the movements of the 

 early Spanish explorers, and to the migrations of animals, 

 especially the buffalo, whose mighty herds in early days were 

 wont to wander north and south across the plains with the 

 changing seasons, and in whose furry coats the burrs of the 

 night-shade might readily have been entangled. The early 



