CHAP, i Processes of Absorption of Water 251 



pass through them, a peculiarity which Traube attributed 

 to the relative sizes of the molecules of the constituents 

 of the membrane and of the transuding salt ; only such 

 being able to pass as had molecules smaller than the micellar 

 interstices of the pellicles. 



Whatever the value of Traube's work may be when 

 subsequent researches are taken into account, it was of 

 great importance at the time in directing more careful 

 attention to the part played by the membrane in osmotic 

 action, and in showing that the old view of osmotic equiva- 

 lence was erroneous, endosmosis being independent of any 

 interchange, and dependent on what is now known as the 

 osmotic pressure of the fluid in contact with the membrane. 



While these researches, more or less purely physical in 

 their nature, were being carried on, Sachs was engaged 

 in making contributions to our knowledge of the subject 

 from the point of view of the relations of the plant and 

 the soil. In 1859 an( ^ J 86o he occupied himself with an 

 investigation into the condition of the soil, with special 

 reference to the distribution of air and water in it and 

 to the relationships of the young roots to both. He further 

 inquired into the mode of effecting such contact between 

 the young roots and the particles of which the soil con- 

 sists, and the water mechanically held by them, as will 

 enable the absorption of the latter to take place. He 

 established the fact that the only water available for the 

 plant is found in the films which surround the particles 

 of rock and other debris, and that water in the interstices 

 of the soil is not only useless, but harmful to the roots, 

 in that it interferes with their supply of air. Sachs dis- 

 covered also the nature of the relationship of the root-hairs 

 to the particles of soil, and showed that the seat of 

 absorptive activity formerly located in the so-called 

 spongiole consisting practically of the root-cap, really 

 existed in the band of root-hairs just behind the apices 



