2o8 EXPERIMENTAL EVOLUTION LECT. 



obtained are interesting. His investigations were 

 made upon amphibious plants. 1 In Ranunculus 

 aquatilis the external differences are well known 

 between the plants which grow in water, and those 

 which live on land, in the length and thickness of the 

 stem, the length of internodes, etc., and if direct ex- 

 periment and observation had not shown that the 

 two forms belong to the same species, they would 

 certainly be considered as different. Important 

 structural differences are also present. If we consider 

 the leaves only, we see that in the aquatic leaf the 

 dichotomies are from eight to ten in number ; the 

 cells are cylindrical with two or three hairs ; the 

 epidermic cells are regularly shaped and contain 

 chlorophyll, and bear but few stomata ; while in the 

 air-inhabiting leaf, dichotomies are from two to six 

 in number ; cells are flattened, without hairs ; epidermic 

 cells are irregular and contain no chlorophyll, while 

 they bear a large number of stomata. The same 

 differences obtain in the leaves of Carex ampullacea 

 as shown here : 



Submerged leaves. Leaves not submerged. 



Epidermic cells long, wide, Very thick cuticle. Nu- 



without stomata. merous stomata. 



2-3 rows of cells with 4-5 rows of cells with abun- 



chlorophyll. dant chlorophyll. 



1 E. Mer, Des Modifications de Forme et de Structure que subissent les 

 Plantes suivant qu'elks vegttent a F Air ou sous V Eau. Bull. Soc. 

 Botanique, 1880, p. 50. 



