40 THE EVOLUTIONIST AT LARGE. 



caterpillar or a tadpole. But the way a plant 

 eats, we all know, is by taking carbon and 

 hydrogen from air and water under the 

 influence of sunlight, and building them up 

 into appropriate compounds in its own body. 

 Certain little green worms or convoluta have 

 the same habit, and live for the most part 

 cheaply off sunlight, making starch out of 

 carbonic acid and water by means of their 

 enclosed chlorophyll, exactly as if they were 

 leaves. Now, as this is what a leaf has to do, 

 its form will almost entirely depend upon the 

 way it is affected by sunlight and the ele- 

 ments around it except, indeed, in so far as 

 it may be called upon to perform other 

 functions, such as those of defence or de- 

 fiance. This crowfoot is a good example of 

 the results produced by such agents. Its 

 lower leaves, which grow under water, are 

 minutely subdivided into little branching lance- 

 like segments ; while its upper ones, which 

 raise their heads above the surface, are broad 

 and united, like the common crowfoot type. 



