222 Biology in America 



California Coast near Monterey. A very pretty example of 

 the response of plants to such climatic changes is given by 

 the common poke-weed (Phytolacca) of the eastern United 

 States. In California the body of the plant grows well, but 

 the flowers are usually reduced and seed is not formed, while 

 at Tucson, on the contrary, the plant body grows low and 

 prostrate, and flowers and fruit are abundant. There are 

 many other changes also, both of leaf and flower. In this 

 instance at least the variations appear to be temporary and 

 not inherited. 



The common water-cress of our eastern ponds and streams, 

 when cultivated out of water, develops enlarged roots, and 

 marked changes in the form of the leaves, the submerged 

 leaves having very narrow, almost thread-like leaflets, while, 

 when grown in the air, the leaflets are broader. 



The results of experimental modification of the form of 

 animals are too numerous for full discussion here. Many 

 of them are cited by Darwin in his different books, and the* 

 majority of them have been obtained by European workers. 

 The seasonal variations (summer and winter) of certain 

 butterflies can be produced at will by temperature control 

 during the pupa stage. Similarly local varieties (northern 

 and southern) of butterflies can be produced by temperature 

 control during the developing period. Differences of color 

 between the sexes can similarly be controlled. The seasonal 

 changes of arctic birds and mammals are well known, and 

 are supposed to have selective value, either for offense or 

 defense. That these changes are at least secondarily depend- 

 ent upon temperature was shown by the experience of the 

 arctic explorer Ross with the lemming, or arctic mouse; 

 which when kept in the ship's cabin in winter retained its 

 gray coat, but when put on deck promptly changed to white. 

 The celebrated experiment with the Porto Santo rabbits 

 recorded by Darwin is supposed to illustrate the influence 

 of climate in changing animals. These rabbits are believed 

 to have originated from the progeny of a single female pro- 

 duced on shipboard about 1418 or 19. According to Darwin 

 these rabbits, when examined by him in 1861, showed marked 

 differences from domestic rabbits, being much smaller and 

 differing in the form of the skull and in color. Four years 

 later however under the influence of the English climate, they 

 had resumed the color of the domestic form. Recently how- 

 ever Mr. Gerrit S. Miller of the U. S. National Museum has 

 claimed that the celebrated Porto Santo rabbits are nothing 

 more nor less than the rabbits native to southern Europe. 

 Even if this is so however it does not invalidate Darwin's 



