AND OF SALINITY. 267 



aquatic ones perishing in air; but if it is only in the 

 course of its development, it can adapt itself to a 

 changed environment. Thus, if a half -formed floating 

 leaf of Ranunculus heterophyllus or of Sagittaria is 

 submerged, "it is at once arrested, and begins to re- 

 adapt itself to water." There are some species, how- 

 ever, such as many algae, which show no power of adap- 

 tation, and can only live entirely under water. 



The converse experiments of growing aquatic plants 

 on land afforded equally striking results. For instance, 

 it was pointed out by Godron,* as long ago as 1839, that 

 whilst Ranunculus aquatilis (Water crowfoot), when 

 wholly submerged, has all its leaves delicately lacini- 

 ated, yet " if the plant is able to send some of its leaves 

 to the surface, they float and assume a very different 

 form, being kidney-shaped and lobed. The same plant 

 when growing entirely out of water presents a very dif- 

 ferent appearance; the stem is short, much divided into 

 branches, which bear a large number of small leaves, 

 cylindrical, much divided, and somewhat thick. If it 

 were not for the floral organs, one would certainly be- 

 lieve in two or three species." Again, Costantin grew 

 a plant of the aquatic form of Peplis Portula on land, 

 and found that the internodes were changed from their 

 elongated form to a short one. The septa of the cor- 

 tical parenchyma of the stem remained homogeneous, 

 instead of being hollowed out into secondary lacunae, 

 and also the number of vessels was increased. Thus 

 there were 53 vessels in the land form of Peplis Por- 

 tula, instead of 25; 12 instead of 4 in Callitriche, and 

 57 instead of 18 in Nasturtium. 

 * Quoted from De Varigny's "Experimental Evolution," p. 97. 



