HOW PLANTS EAT. 41 



usually broad and expanded, as in the tobacco- 

 plant and the sunflower. Where the plants 

 grow thick and close in meadows, the leaves 

 are mostly long and narrow, like grasses. In 

 overgrown clumps and hedgerows they are 

 generally much subdivided into numerous little 

 leaflets, as is the case with most ferns, and also 

 with herb-Eobert, chervil, milfoil, and vetches. 

 In these last cases, the plant wants to get as 

 much of the floating carbonic acid, and of the 

 sunlight, as it can ; and therefore it makes its 

 leaves into a sort of divided network, so as to 

 entrap the smallest passing atom of carbon, and 

 to intercept such stray rays of broken sunlight 

 as have not been caught by the taller plants 

 above it. In almost all cases, too, the leaves 

 on the same plant are so arranged round the 

 stem and on the branches as to interfere with 

 one another as little as possible ; they are placed 

 in an order which allows the sunshine to reach 

 every leaf, and which secures a free passage of 

 air between them. 



An interesting example of the way some of 

 these principles work out in practice is afforded 

 us by a common little English pond-weed, the 

 water-crowfoot. This curious plant grows in 

 streams and lakes, and has two quite different 

 types of leaves, one floating, and one submerged. 

 The floating leaves have plenty of room to develop 

 themselves freely on the surface of the pond; 

 they loll on the top, well supported by the mass 

 of water beneath ; and, as there is little compe- 

 tition, they can get an almost unlimited supply 

 of carbonic acid and sunshine, Therefore, they 



