1 82 Chapters in Modern Botany CHAP. 



Let us take the case of the white water - buttercup 

 (Ranunculus aquatilts) as a subject for interpretation. The 

 facts are that the floating surface - leaves are more or less 

 simple and rounded, and that the submerged leaves are 

 divided into hair-like segments ; and it is also known that if 

 the plants grow in swiftly running water all the leaves are 

 submerged and filiform, while if they grow altogether on 

 the mud by the side of the stream the dissected type of 

 leaf is lost and the appearance of the plant is very different. 

 So much so, indeed, that Lamarck believed that Ranunculus 

 aquatilis might .thus be transformed into an allied species 

 R. hederacea, but this conclusion has been denied by 

 Godron, who has paid great attention to the variations of 

 buttercups. It is certain, however, that the predominant 

 type of leaf varies according to the surroundings, and that 

 each form of leaf is advantageously adapted to its condi- 

 tions. How is this to be interpreted? 



Sir John Lubbock says, " Of course it is important to 

 expose as large a surface as may be to the action of the 

 water. We know that the gills of fish consist of a number 

 of thin plates, which while in water float apart, but have not 

 sufficient consistence to support even their own weight, 

 much less any external force, and consequently collapse in 

 air. The same thing happens with thin, finely-cut leaves. 

 In still water they afford the greatest possible extent of 

 surface with the least expenditure of effort in the formation 

 of skeleton. This is, I believe, the explanation of the 

 prevalence of this form in subaqueous leaves." 



Mr. Grant Allen, on the other hand, interprets the finely- 

 divided form of the submerged leaves to the relative 

 scarcity of carbonic acid gas in the water. 



Our view of the problem is as follows : First, we must 

 take note of the manner in which the "veins" of the leaf 

 are distributed in different species of Ranunculus, especially 



