Translocation in Plant Tissues . 
299 
plant, although in most tissues considerable restrictions are placed on speedy 
transference in quantity from cell to cell owing to the extreme tenuity and 
comparatively small number of the threads, which oppose rapid motion in 
much the same way as turnstiles at a barrier limit the rate of passing of 
a crowd of people from one side to the other. 
Similar considerations would apply to the case of a normal green foliage 
leaf. The sugar formed in the mesophyll would be able to pass from cell to 
cell by way of the connecting-threads, and so would reach the protoplasm 
of the bundle-sheath cells near the endings of the fine veins. Its farther 
path will be dealt with later on. 
At all regions in the plant where meristematic tissue occurs, and 
especially at the cambium, and at the apices of roots and shoots, or where 
storage is going on, as well as throughout the whole of the living tissues 
which are continually undergoing respiration, great consumption of soluble 
carbohydrates occurs. This means that in such cells the concentration of 
these substances is continually varying. 
To form starch reserves, or new cell walls, or to produce fibres or 
‘stone-cells sugar must be withdrawn and its concentration become lowered 
temporarily at the place of withdrawal. 
Any such lowering of concentration at one point of the protoplasm will 
affect the state of equilibrium which should obtain, as described above. 
For example, if the sugar concentration is lowered at the surface of 
a particular protoplasmic particle, then more will pass from the immediately 
adjacent solution to become concentrated at the surface of this particle in 
order to re-establish the specific relation. 
The solution will accordingly become locally weaker, and this will 
disturb the equilibrium between it and other particles in the vicinity ; the 
latter will therefore give up a portion of their adsorbed solute, diffusion in 
the solvent will occur, and its effects be transmitted. 
If carbohydrate consumption is vigorous, or long continued, its influence 
will be far-reaching. 
Thus a wave of disturbance and readjustment of equilibrium is pro- 
pagated, in much the same way as the firing of shells from a battery leads 
to the depletion of the immediate supply, followed by a replenishing from 
the reserves, &c., and ultimately from the factory, so that the scheduled 
relations are maintained between the various stores at intermediate points. 
Waves of this type will be sent out from all points where sugar is being 
transformed, and they will spread in all directions subject to structural 
limitations. 
To a certain extent the cell vacuoles may be compared to a series of 
small water-tanks from each of which supplies may be drawn off by several 
pipes, and to which the losses may be made good by small-bored pipes 
connecting the bases of adjacent tanks. The small tanks must be imagined 
