TBANSLOCATION OF NUTKITIVE MATEEIALS 223 



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 being 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 



