94 EXPERIMENTAL EVOLUTION LECT. 



the Lake of Constance are less regular in form, more 

 abrupt, he thinks on account of the movements of the 

 water of the Lake. 



Baudin also considers Pisidium pulchellum and 

 cinereum as two forms of the same species, and 

 Locard himself has discovered through experiments 

 that L. turgida and elophila are mere varieties due 

 to environment of the common Lymncea stagnalis. 

 He says : " These are not new species, but merely 

 different aspects of a common type, which is capable 

 of modification and of adaptation according to the 

 nature of the media in which it has to live." Bateson 

 has recently observed similar facts concerning Cardium 

 edule ; Locard shows how extensively any one species 

 Unio rhomboideus for instance varies in forma 

 and in colore according to its habitat, lake, river, or 

 torrent, and an indefinite number of such instances 

 might be quoted here. The same may be said con- 

 cerning plants. All know that in different stations the 

 same species exhibits considerable differences in form, 

 in the comparative height of the stems, in the number, 

 length, distance of the branches, and so on, and ex- 

 perienced practical botanists easily recognize through 

 these differences the origin of an individual plant, 

 detecting whether it has grown in a valley or on the 

 Alps, in dry or in moist soil, in an exposed or in a 

 protected station, As the well-known fungologist, 



