PLANTS AND THEIR SURROUNDINGS 267 



hillsides are never so large as those that grow in the older 

 valleys. The greatest forests in the world are in the 

 valleys of ancient, slow-flowing rivers. The greatest of 

 all are in the valley of the Amazon. 



In North America the number of kinds of trees is much 

 less than in the tropics. There are about twenty kinds 

 that every one should learn to know. They are quite 

 easy to recognize if you will practise observing them very 

 carefully when some one tells you the names. You must 

 practise picking out the characters by which you will know 

 them the next time you see them. Oak, maple, ash, elm, 

 and hickory are trees you all should know, and there are 

 several kinds of each one of these that you will soon learn 

 to know if you take any interest in plants. 



Now going back to the woods in April. Why is it that 

 so many beautiful flowers are to be found there in spring, 

 while in summer we find hardly any at all? Hepatica, 

 violets, spring-beauty, bloodroot, trillium, Dutchman's- 

 breeches do you know these flowers ? In April and May 

 you can find all of these and many more. But in July and 

 August the woods are bare of flowers. Why? 



This fact shows how very responsive plants may be to 

 their environment. A woods is a sort of "plant society." 

 In swamps, thickets, or meadows we find other kinds of 

 plant societies. Every society, plant or human, has its 

 more and its less prominent members. The trees are the 

 prominent, controlling members of forest societies. The 

 other plants have to adjust themselves to the great, success- 

 ful trees. The trees are the forms that have made sure of 

 the light and of the moisture. Their leaves are high in 

 the air and their roots deep in the soil. The undergrowth 

 must do the best it can with the light that filters through. 



