72 TRANSLOCATION IN PLANTS 



That transpiration is likely to influence salt absorption 

 indirectly through its effect on metabolism and growth 

 is without doubt, but the ultimate effect is determined 

 less by transpiration and more by the effect on the plant 

 and one cannot predict whether an increase in transpiration 

 will increase or decrease salt absorption. The data given 

 by Muenscher clearly indicate that the methods used to 

 alter transpiration, rather than differences in transpiration 

 themselves, are chiefly responsible for differences in ash 

 contents. 



Most of the investigators who have studied the effects of 

 transpiration on ash absorption have studied the effect on 

 total ash and not that on the individual constituents. It 

 is highly probable that different constituents will be 

 influenced differently, not, however, because transpiration 

 directly influences the absorption of different ions, but 

 because it is likely to alter metabolism and thus alter the 

 proportion of ash constituents. The differential absorp- 

 tion of ions would probably be more influenced by the 

 factors used to alter transpiration than by the total tran- 

 spiration as such. For example, an increase in transpira- 

 tion brought about by raising the temperature would 

 probably have a different effect than an increase brought 

 about by low humidity or by increased light intensity. 

 Schloesing (1869) claimed that high transpiration of 

 tobacco plants in the open increased the absorption of 

 inessential elements, while relatively greater amounts of 

 essential elements were absorbed by the plants in the humid 

 chamber with low transpiration. His data, however, show 

 a greater quantity of four of the essential elements in 

 the dry chamber and only three in the humid chamber. 

 Though considerable emphasis is laid upon this early work 

 of Schloesing, especially in a number of textbooks on plant 

 physiology, notably in Palladin's "Plant Physiology" 

 (1926), it should be remembered that the leaves of only 

 one plant were analyzed from the humid chamber. This 

 one plant was grown in the humid chamber for a period 

 of 30 days, while the three check plants were grown in 



