50 



LEAVES 



Compound Leaves. — Leaves which are composed of two or 

 more leatiets arising from a single petiole are said to be com- 

 pound and are described as iMlmale- or radiate-compound (Fig, 

 38), or as pinnate- or feather-compound. (Fig. 39.) The size, 

 form, arrangement and various other modifications of the leaves 

 of plants are largely dependent upon the environmental factoi'S, 



Fig. 38. — Palmately compound leaf. 



Fig. 39. — Pinnately compound leaf. 



especially light and moisture. Land plants, growing in very 

 wet surroundings tend to have larger leaves than those growing 

 in dry or arid surroundings. Aquatic plants in running water 

 tend to have long, narrow leaves as compared with plants living 

 in still water. 



The Leaf Blade. — The veination of the leaves supports a 

 delicate structure (Page 102), within which are numerous air 



