304 USEFUL AND HARMFUL PLANTS 



ample, there is the influence of forests upon water-supply, 

 by which is meant their action as reservoirs feeding the 

 streams gradually in spring, thereby avoiding floods, and 

 at the same time keeping back plenty for the dry season. 

 Then, too, there is the im})ortant action of plants in soil- 

 making, and the purifying influence of vegetation upon air 

 and water whereby they are made to serve better the needs 

 of animal life. 



All these various relations of plants to the life of the world, 

 and to our own lives in particular, are as profitable and 

 attractive matters of study as any that have claimed our 

 attention; and the student will do well to learn all he can 

 regarding them. It should be said, however, that many of 

 these relations are best understood in the light of vegetable 

 biology. Moreover, the student's pursuit of economic botany 

 cannot well proceed much farther than we have here at- 

 tempted to go, without his first acquiring such an elementary 

 knowledge of systematic botany as the following chapters may 

 help him to gain. 



