230 J. H. MAIDEN. 



soil which would be covered by them, Hartig thought the 

 transpiration of a forest less, Schiibler found it 0*6 for the 

 forest and 3*0 to 5*0 for the sod. Marie-Davy found it, for 

 firs 1*18, for beeches 1*32, for sod 1'86. 



The quantity of water so used is as variable as the 

 amount of precipitation, and in fact within certain limits 

 depends largely upon it. That is to say, a plant will tran- 

 spire in proportion to the amount of water which is at its 

 disposal. Transpiration is also dependent on the stage of 

 development of the plant, on the nature of its leaves and 

 the amount of its foliage, on temperature, humidity, and 

 circulation of the air, on the intensity of the sunlight, and 

 on temperature and structure of the soil and other meteoro- 

 logical conditions. Rain and dew reduce the transpiration, 

 wind increases it. The amount of transpiration depends 

 considerably on the thickness of the leaves, therefore the 

 surface of the foliage is not a reliable measure, but should 

 be compared with the weight. With so many factors to 

 vary them, the values which may be given for the amount 

 of transpiration of various kinds of trees, can only be 

 approximations of its range within wide limits. (Harring- 

 ton, op. cit.) 



"All vegetation takes up a certain amount of water, a part of 

 which is consumed in building up its body, and a still larger part 

 returned to the atmosphere by transpiration during the growth." 



The factor of dissipation having been fully discussed, it 

 need not be further considered here, except to recall the 

 conclusion that forest growth transpires considerably less 

 than other kinds of vegetation. 



Since this water is given off again to the atmosphere in 

 the locality where it has fallen — thus enriching the atmo- 

 spheric moisture — and is therefore only diverted tempo- 

 rarily for the purpose of doing duty in producing useful 

 substance and retaining it in the locality where it has 



