Translocation in Plant Tissues . 
309 
the cumbersome and uneconomical method of providing for translocation 
which had existed in Lepidodendron and its contemporaries. 
On the hypothesis of translocatory mechanism here put forward it can 
be seen that in Lepidodendron there was little, if any, physiological necessity 
for the development of cells comparable with the sieve-tubes of more recent 
plants. 
Summary. 
The paper is the outcome of an attempt to form a mental picture, in 
terms of physical chemistry, of what goes on in the plant cell during certain 
phases of sugar translocation. 
The work of recent years tends to show that protoplasm contains 
proteins and lipoids among other substances, and that these form with 
water a complex colloidal system. 
It is probable that one or more constituents are present as gels. 
In so far as the component substances are free to move they must be 
disposed in accordance with their power of lowering the energy of the 
system ; protoplasm may therefore exhibit stratification. 
Definite relations have been found to obtain between the concentration 
of a solute at the surface of adsorbing particles introduced into the solution 
and the concentration of the solute in the solvent. This state of equilibrium 
is reversible. 
The case of charcoal and acetic acid is cited. 
Adsorption compounds of albumen, lecithin, and glucose are known. 
It is suggested that in vegetable protoplasm there are present con- 
stituents capable of adsorbing sugars from solution. 
For any given concentration of sugar present in the liquid phase of the 
protoplasm, and the cell sap continuous with it, there would be a definite 
concentration of sugar present at the adsorbing surface. 
Any alteration of concentration in either region would lead to a re- 
adjustment of concentration equilibrium, which would be propagated as 
a wave through the system composed of the adsorbing particles and the 
solution immediately in contact with them. 
The rate of propagation of this wave would depend very much upon 
the degree of approximation of the particles under consideration, and would 
increase as the distance between them decreased. 
Connecting-threads are assumed to provide a continuous protoplasmic 
pathway, though they impose restrictions varying with their frequency and 
tenuity. 
The structure of the sieve-tube is considered, and it is shown that the 
sieve-plate would cause little, if any, obstruction to the progress of the wave 
of readjustment of concentration equilibrium, so that the sieve-tube would 
