Studies in Forestry 



[CHAP. IV. 



capacity for regulating and maintaining as steady a rate of 

 transpiration as possible. For all kinds of woodland crops, 

 however, there is on the one hand a minimum supply of 

 water requisite for thriving and for healthy development, and 

 on the other a maximum normal limit beyond which any 

 surplus of soil-moisture is prejudicial to their well-being. 

 Although, with decreased transpiration, the process of assimi- 

 lation may not be essentially interfered with, yet the imbi- 

 bition of soluble salts is considerably decreased, and the 

 amount of ashes or mineral constituents contained in the wood 

 is less than in timber produced in a drier atmosphere. 



Observations relative to the amount of water transpired by woodland 

 crops were made by von Honel in experiments made in 1879-1881. He 

 found that, with the exception of the deciduous Larch, conifers transpire 

 on the average only about one-sixth to one-tenth of the quantity of 

 water that is evaporated by broad-leaved trees l . 



Taking the average of these three years, his experiments led to the 

 result that the average transpiration of water per 100 grammes (0-22 Ibs.) 

 of dry leaf-substance amounted during the active period of vegetation 

 annually to the following number of Kilogrammes (2-204 Ibs.) : 



He also found that, whilst in conifers transpiration is greatest from 

 foliage fully exposed to insolation, in broad-leaved trees it was greatest 

 from foliage growing in shade, as the following table shows : 



1 See Ramann, op. cit., pp. 309-312. 



