142 TRANSLOCATION IN PLANTS 



is a mass flow through these plasmodesma which is due 

 to a turgor pressure gradient, but he seems to consider it a 

 flow of food solution and not protoplasm. For a con- 

 siderable period since the time of Lecomte's papers no 

 great attention was directed toward solution of the problem 

 concerning the mechanism of transport. 



Mangham (1917) suggested a hypothesis by which he 

 attempted to explain the movement of sugars through 

 phloem cells as if it were controlled by adsorption. He 

 pointed out the probable continuity of colloidal proto- 

 plasmic material from sieve tube to sieve tube through 

 the sieve pores and between these and other cells through 

 plasmodesma. Then, recognizing the fact of a dynamic 

 equilibrium between adsorbing colloidal material and an 

 adsorbed substance, he suggested that the removal of 

 sugar molecules from the adsorbent in a receiving cell 

 would upset this equilibrium and result in a disturbance 

 which would be propagated as a wave of readjustment 

 through the continuous mass of colloidal material thus 

 tending to move the sugar along such a mass through its 

 entire length. He suggested that the rate of propagation 

 of this wave would depend upon the degree of approxima- 

 tion of the adsorbing particles. Maugham's hypothesis 

 is, however, based on a wrong assumption, for he failed to 

 realize the fact, that adsorbed molecules are not attracted 

 to the adsorbent from a distance but diffuse to the surface, 

 and that they would be hindered in their movement by a 

 stationary adsorbent and not hastened. When a molecule 

 or ion is adsorbed by a colloidal mass, its diffusion through 

 that mass tends to be retarded and not accelerated as 

 can be easily demonstrated in experiments on the relative 

 rates of movement of adsorbed and nonadsorbed solutes 

 through gelatin, agar, filter paper, and such colloidal 

 masses. Kidd (1918) has published a short note criticizing 

 Maugham's interpretation. 



One distinctly valuable suggestion of Maugham's is that 

 offering an explanation for a rapid interchange of materials, 

 such as sugars, between one living cell and another, whereas 



