TRANSLOCATION OF NUTRITIVE MATERIALS 228 
points of the stem and root. So long as it is being used 
by the protoplasm in these regions, the sap of the cells of 
the tissue there, which are using it in the construction of 
living substance, becomes continually weaker in that con- 
stituent, and hence more and more makes its way into them 
to equalise the concentration. The utilisation or consump- 
tion of the sugar so acts as an attracting force, directing 
the stream to the points where it is required. The same 
principle applies to the consideration of the deposition of 
the large reserves of carbohydrates in seeds, tubers, or 
other organs. The withdrawal of it from the travelling 
stream, which is the result of the formation of the quantities 
of starch or cellulose which those reservoirs contain, leads 
to fresh quantities bemg transported slowly but con- 
tinuously to those cells, owing to the same physical pro- 
cesses. The stream passes, in fact, in both cases exactly in 
proportion as the consumption takes place, whether the 
consumption takes the form of construction of new proto- 
plasm, or the transformation of the travelling carbohydrates 
into the insoluble resting forms. . 
This passage of the sugar about the plant need not demand 
a coincident transport of water, so that the old idea that 
there was an actual stream of fluid along the bast, or in 
the old nomenclature a stream of descending sap, need not 
have any foundation in fact. The principle of diffusion 
and the action of the protoplasm will explain the passage 
of the sugar. Disturbances of the fluid contents of the 
cells do no doubt occur, as osmosis is continually taking 
place in both directions between the contiguous cells. A defi- 
nite flow of water need not, however, coincide in either mag- 
nitude or direction with the passage of the stream of sugar. 
The translocation of the sugar, we see, thus varies in 
direction and in magnitude according to the varying pro- 
cesses which are from time to time proceeding. As the 
variations in these processes, particularly those of growth 
and nutrition, are often sudden and considerable, we find 
the translocation is generally accompanied by changes of 
