June, 1922] MUENSCHER — ABSORPTION OF SALTS 3I3 



growth. by plants growing in habitats where transpiration is reduced with 

 that by plants growing in habitats where conditions for transpiration are 

 more favorable. Among these may be cited the work of Schimper upon 

 halophytes, and the work of Haberlandt, Burgerstein and his co-workers, 

 and McLean upon transpiration by plants in tropical rain forests. 



Schimper (1891) pointed out that the xerophytic modifications of halo- 

 phytes serve to reduce transpiration and also the absorption of salts. Al- 

 though he does not say that salts enter with the water, he assumes a relation 

 between transpiration and the absorption of salts when he states that re- 

 duced transpiration also reduces the absorption of salt and protects the 

 plant from the danger of too much salt accumulating in the leaves. The 

 works of Stahl (1894) and others offer better explanations for the occurrence 

 of xerophytic adaptations among halophytes. 



Haberlandt (1892) first definitely suggested that there is no relation 

 between transpiration and the quantity of mineral nutrients absorbed from 

 the soil. He maintained that diffusion independently of transpiration 

 causes the movement of salts from the roots to the highest parts of plants. 

 Transpiration is only one factor and not the important one in the movement 

 of salts. Haberlandt presented data to show that the rate of transpiration 

 in tropical forests is less than in central Europe. High relative humidity 

 in spite of high temperatures reduces the transpiration in the tropics. Not 

 all workers agree with Haberlandt. In opposition to Haberlandt, Burger- 

 stein (1897), Stahl (1894), and Giltay (1897) claimed that the plants in the 

 tropical rain forests transpire more than those in a temperate region such as 

 central Europe. It is beside the question to discuss the validity of claims 

 made by the opponents in this controversy. It will suffice here to point 

 out that Haberlandt, who believed that the transpiration in the tropics is 

 not higher than in central Europe, also maintained that transpiration is 

 not necessary for the absorption of salts; while Burgerstein and his follow- 

 ers, who believed that the transpiration in the tropics is very high, adhered 

 to the theory that there is a relation between transpiration and the absorp- 

 tion of salts. Burgerstein said that a green plant in synthesizing large 

 quantities of organic matter needs large quantities of inorganic nutrients, 

 and that, since these are in a very dilute solution in the soil water, the plant 

 must take up large amounts of this solution and transpire the excess water. 

 Since only a small amount of this water is used in synthesis, transpiration 

 makes it possible for a plant to conduct large quantities of water and nutri- 

 ents to the assimilating tissues in a short time. 



McLean (1919) worked with plants of the tropical rain forests of Brazil. 

 He found that leaves taken from the plants growing under these conditions 

 of assumed depressed transpiration showed a higher ash content relative to 

 the total assimilates than sun plants. This he takes to indicate that 



The absorption of mineral salts is 'independent at least of foliar evaporation, the most 

 complete suppression of which is thus seen to be of only secondary importance to the plant . 



