304 USEFUL AND HARMFUL PLANTS 



ample, there is th(> influence of forests upon water-sujDply, 

 by which is meant their action as reservoirs feeding the 

 streams gradually in spring, thereby avoiding floods, and 

 at the same tim(_' keeping back plenty for the dry season. 

 Then, too, theri> is tlie important action of plants in soil- 

 making, and the ]iurifying influence of A'egetation upon air 

 and water whereby the}- are matle to serve better the needs 

 of animal life. 



All these various relations (_if ])lants to the life of the world, 

 and to our own» lives in ]:iarticular, are as jjrofitable and 

 attractive matters of study as any that have claimed our 

 attention; and the student will do well to leai-n all he can 

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

 these relations are best understood in the light of vegetable 

 biology. A-Ioreover, the student's ])ursuit of economic liotan}' 

 cannot well proceed much faither than we have here at- 

 tempted to go, without his first acquiring such an elementary 

 knowledge of systematic botauj' as the following chapters may 

 help him to gain. 



