CHAP, i Processes of Absorption of Water 259 



This inclusion of transpiration among the vital phenomena 

 marks a great development in the explanation of the process 

 and its importance. 



Sachs co-ordinated the function of transpiration more 

 closely than had been done before, with the absorptive 

 activities of the roots, by showing that it varies with the 

 temperature of the soil in which the roots are growing and 

 with the nature of the soil itself. The latter observation 

 had been previously made by Senebier, but his experiments 

 were on a much more limited scale than those of Sachs. 

 The latter found that a Tobacco-plant growing in coarse 

 sand gave off less water than another growing in clay ; 

 he investigated the effects of adding various salts to the 

 water to be absorbed, and observed that dilute acids 

 increased, while dilute alkalies restrained transpiration, as 

 did most of the neutral salts with which he experimented. 



Sachs' work was followed by that of Biirgerstein in 1876. 

 This showed that nitric acid and carbonic acid increase 

 the exhalation of vapour, and that so long as very dilute 

 solutions are used, a greater concentration of the salt still 

 further increases the amount. The results of his experi- 

 ments with various salts showed, in his opinion, that trans- 

 piration increases with the concentration of the solution 

 of the salt up to a certain maximum, beyond which it 

 gradually diminishes, becoming gradually less than when 

 the roots are in distilled water. 



In 1880 Vesque also wrote on the correlation between 

 transpiration and absorption, confirming Sachs, but asso- 

 ciating the variations of transpiration with differences of 

 rate of absorption from the various soils, making the 

 dependence on the salts only secondary or indirect. 



The observations of Hales on the quantities of water 

 which are transpired by trees were for a long time un- 

 checked. Experiments with a view to a more carefully 

 controlled result were made in 1877 by F. Haberlandt, and 



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