98 EXPERIMENTAL EVOLUTION LECT. 



of floating horizontally. Similar variations in form 

 are to be observed in Myriophyllum verticillatum and 

 Juncus supinus, and many other plants. Polygonum 

 amphibiiun also exhibits important morphological 

 variations. When growing out of water it has lanceo- 

 lated, downy leaves, with short stalks, and covered 

 with stomata on both faces, while the same leaves, if 

 the plant is growing under water, are deprived of hair, 

 have a long stalk, a,nd are obtuse, without stomata on 

 the lower side. These two forms of leaves are often 

 met with on the same plant, where it has been, 

 through accidental circumstances, growing for some 

 time under water and for some time out of water. 

 Ch. Martins 1 notices similar facts concerning Jussicea 

 grandiflora, where the variations are even more im- 

 portant. Every one may notice in our common ivy 

 considerable variations in the form of leaves, and these 

 variations are also to be seen in other plants, in fact 

 they are more or less present in most plants, and 

 careful investigation will disclose their number and 

 importance. 2 These variations, which seem to be of 

 no account as far as the general life of the plant is 

 concerned, may however be accompanied by important 



1 Observations sur la Jussicea grandiflora, in Bull. Soc. Botanique 

 de France, vol. xiii. p. 176. 



2 G. Fournier : Recherches Anatomiques et Taxonomiques stir la 

 Famille des Crucijeres, 1868, and also Faivre : La Variabilite des 

 Especes et ses Li mites, 1868. 



