398 HOW CROPS GROW. 



in water, to cause a rapid passage of water through a 

 membrane in the same manner from its power of imbibi- 

 tion, although here there could be no exosmose or out- 

 ward movement. 



The application of these facts and principles to explain- 

 ing the movements of the liquids of the plant is obvious. 

 The cells and the tissues composed of cells furnish pre- 

 cisely the conditions for the manifestation of motion by 

 the imbibition of liquids and by simple diffusion, as well 

 as by osmose. The disturbances needful to maintain 

 motion are to be found in the chemical changes that 

 accompany the processes of nutrition. The substances 

 that normally exist in the vegetable cells are numerous, 

 and they suffer remarkable transformations, both in 

 chemical constitution and in physical properties. The 

 rapidly-diffusible salts that are presented to the plant by 

 the soil, and the equally diffusible sugar and organic 

 acids that are generated in the leaf-cells, are, in part, 

 converted into the sluggish, soluble colloids, soluble 

 starch, dextrin, albumin, etc., or are deposited as solid 

 matters in the cells or upon their walls. Thus the dif- 

 fusible contents of the plant not only, but the mem- 

 branes which occasion and direct osmose, are subject to 

 perpetual alterations in their nature. More than this, 

 the plant grows ; new cells, new membranes, new pro- 

 portions of soluble and diffusible matters, are unceas- 

 ingly brought into existence. Imbibition in the cell- 

 membranes and their solid, colloid contents, Diffusion 

 in the liquid contents of the individual cells, and Osmose 

 between the liquids and dissolved matters and the mem- 

 branes, or colloid contents of the cells, must unavoid- 

 ably take place. 



That we cannot follow the details of these kinds of 

 action in the plant does not invalidate the fact of their 

 operation. The plant is so complicated and presents 

 such a number and variety of changes in its growth, 



