2 INTRODUCTION. 



to the closer study of any one of them, or of phenomena connected 

 with them in such of the less complicated vegetable structures as 

 supply facilities for the study of these phenomena free from compli- 

 cations which are met with in such masses of vegetation as are met 

 with in forests ; and by reasoning from the lesser to the greater, as 

 well as from the greater to the less, we may attain to what are at 

 once clearer and more compi'ehensive views of the truth on the 

 subject. This'is what I propose to do in the sequel. 



To prevent misapprehension I may call attention to the circum- 

 stance that in treating of humidity it is not the rainfall alone of which 

 I speak. I attribute not a little of the prevalent popular opinions in 

 regard to the effects of forests, and controversies in regard to these to 

 the difference between these being overlooked. 



