210 EXPERIMENTAL EVOLUTION LECT. 



shore and inland life on different individuals of the 

 same species, the number of species investigated 

 being eighty-five. The results have been that in 

 fifty-four species leaves are thicker in the vicinity 

 of the sea than in inland individuals ; in twenty-seven 

 species no difference is apparent ; and in four, leaves 

 are thicker inland than near the sea. If we consider 

 that of the fifty-four species above mentioned, seven- 

 teen are shore-inhabiting plants, while thirty-seven 

 live preferably inland, it is obvious that, generally 

 speaking, inland plants acquire thicker leaves when 

 living in the vicinity of salt water. So much for the 

 external characters. Now if we consider internal 

 characters, many differences are detected which ex- 

 plain the presence of the external differences, and 

 these differences are observable in all parts of the 

 leaves. Epidermic cells are larger in twenty-three 

 shore plants, but in thirty-one there is no differ- 

 ence, while in four the difference turns to the advan- 

 tage of inland plants. Here, then, the influence 

 makes itself but little felt. The case is quite altered 

 when the mesophyll is considered, for while in eleven 

 species there is no difference, in all others the palisade 

 cells are either more numerous or attain greater 

 thickness, or exhibit both characters at once, and 

 at the same time the interspaces which underlie 

 the stratum of palisade-cells are much reduced. The 



