78 Studies in Forestry [CHAP. iv. 



less in our damp insular climate than in the inland tracts of the continent 

 of Europe with their much drier climate and consequently enhanced 

 activity of transpiration. There are many places along the east coast of 

 England where even the total average annual rainfall is less than 12 inches, 

 and where timber crops are still capable of thriving perfectly well. 



Of much more practical interest than von Honel's experi- 

 ments must be considered the investigations that have more 

 recently been made by Ebermayer with a view to determine 

 the relative transpiration of the different kinds of forest trees, 

 and the results of which correspond better than von Honel's 

 with the facts of actual sylvicultural experience. Ebermayer 

 analyzed foliage for the purpose of determining this by means 

 of the percentage of water contained in the fresh leaves, and of 

 *pure mineral ash obtained afterwards from the combustion 

 of the dry leaf-tissue. The former table is now given, whilst 

 that relating to the mineral ash will be referred to later on. It 

 need only be remarked that, as the nutrient salts are imbibed 

 in a weak solution, and as the water is mostly transpired 

 through the foliage in the form of aqueous vapour, whilst the 

 salts eliminated are to a great extent deposited within the leaf- 

 tissue, a steady and normal degree of transpiration is essential 

 for the due conduct of the nutritive processes and the well-being 

 of the trees ; but during sunlight, and also in warm dry situa- 

 tions, the rate of transpiration is of course greater than in 

 shadow, or in cool, damp exposures, and at high localities 

 where the relative humidity of the air is great. Hence, coeteris 

 paribus, it seems justifiable to conclude that leaves, which 

 show large accumulations of pure mineral ash within them, 

 not only make larger demands for mineral nutrients per unit 

 of weight of foliage, but also at the same time transpire more 

 water through their leaves in order to concentrate these de- 

 posits. For the solutions taken up by the rootlets of various 

 kinds of trees do not appear to vary much as regards strength 

 (except in localities like Alder swamps where the solutions are 

 abnormally weak), although of course in fertile soils (or on 



