9* 



In reality the distribution of this sugar solution does not take 

 place in any definite and determined direction, but can take 

 place through the parenchyma cells of the plant in any direc- 

 tion whatever, upwards as well as downwards, by simple diffu- 

 sion to those parts where it is required, i. e., to those parts where 

 growth is going on, and where there is a deficiency of sugar in 

 consequence of a consumption of sugar material, and hence 

 where there is a demand being set up for it. Thus, if we imagine 

 a cell dividing and getting poor in sugar, in a plant in which, to 

 begin with, all the cells were in equilibrium, that is to say, 

 possessed of an equal supply of sugar or starch, immediately a 

 demand is created from cell to cell throughout the whole plant 

 for sugar solution, which passes by diffusion towards that point 

 in all directions until equilibrium is again established. The 

 distribution of this sugar solution in the plant depends, then, 

 on the processes going on within the plant, which are using the 

 sugar up in various ways. Consequently, the course of this 

 sugar solution is very different at different seasons, since 

 growth varies at different times. In spring we have active 

 growth of the leaves, and growth of the wood in the stem and 

 in the root, both in length and thickness. As the leaves form 

 this sugar solution it is clear that when they are in the pro- 

 cess of development they cannot form it for their own growth. 

 The growth of the leaves takes place by means of the use of 

 the reserve food material, such as aleurone and starch ; hence 

 in spring the current of sugar solution is not from the leaves 

 to somewhere else, but from the reservoir, wherever it may 

 be, upwards towards the growing organs — e. g., leaves, flowers, 

 &c, where it is being consumed to supply the material for the 

 growing cells, and promote the development of those organs. 

 When the leaves are formed, and active growth goes on in the 

 stem, roots, and flowers, the direction of the current of the sugar 

 solution is then, as I have stated, from the leaves to every part 

 where growth is taking place; hence in summer its course is an 

 indeterminate one. In the autumn we have less active growth, 

 and the plant is then producing seed or laying up stores of starch 

 and other substances for the supply of the next spring, so the 



