TRANSLOCATION OF NUTRITIVE MATERIALS 217 
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 diffuses 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 being transported slowly but con- 
tinuously to those cells, owing to the same physical pro- 
cesses already described. The stream passes in fact in 
both cases exactly in proportion as the consumption takes 
place, whether the consumption takes the form of construc- 
tion of new protoplasm, or the transformation of the travel- 
ling 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 alone will suffice to explain the passage of the 
sugar. Disturbances of the fluid contents of the cells dono 
doubt occur, as osmosis is continually taking place in both 
directions between the contiguous cells. A definite flow of 
water need not, however, coincide in either magnitude 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 
the carbohydrate from the labile to the storage forms, and- 
vice versd. Itis very usual to find temporary accumulations 
