FOKESTS IN THEIR RELATION TO RAINFALL. 231 



fallen for a longer time, transpiration may even be con- 

 sidered as an element of conservation. 



There is still to be considered a certain amount of moisture 

 which is retained and stored up in the body of the plant, 

 partly as a necessary permanent constituent, partly as a 

 temporary constituent, being evaporated when the plant 

 dies or the wood is seasoned. The amounts thus retained 

 vary considerably according to age, capacity for transpir- 

 ation, site, soil, climate, density, slow or rapid growth, 

 weather, seasons, and even the time of day. It is there- 

 fore almost impossible to give anything but very rough 

 approximations, especially as also the different parts of the 

 tree vary considerably in the amounts of water present. 

 (Fernow, op. cit.) 



VIII. Some Uses of Forests. 



a. To Temper Floods. — I have dealt with this subject in 

 a former paper, 1 hence I propose to give more cursory treat- 

 ment in this place than its importance demands. I think 

 very few men will dispute the good effects of forests miti- 

 gating the effects of downpours of rain in regard to the 

 flow of water-courses. 



"The effects of forests in retarding the flow of the rainfall after 

 its precipitation has been established, I consider, beyond all 

 question." 2 



"Already the rivers that rise in those regions (Northern United 

 States), flow with diminished currents in dry seasons, and with 

 augmented volumes of water after heavy rains. They bring down 

 larger quantities of sediment, and the increasing obstruction to 

 the navigation of the Hudson, which are extending themselves 

 down the channel in proportion as the fields are encroaching on 

 the forests, give good grounds for the fear of irreparable injury to 

 the commerce of the important towns on the upper waters of that 



1 " The Mitigation of Floods in the Hunter River," ante p. 107. 



2 J. Croumbie Brown, op. cit. 



