406 HOW CROPS GEOV/. 



and diffuse out of the cells, but the water remains color- 

 less for several days. The pigment is, however, soluble 

 in water, as is seen at once by' crushing the beet, where- 

 by the cells are forcibly broken open and their contents 

 displaced. The cell-membranes of tlie uninjured root 

 are thus apparently able to withstand the solvent power 

 of water upon the pigment and to restrain the latter 

 from diffusive motion. Upon subjecting the slice of 

 beet to cold until it is thoroughly frozen, and then plac- 

 ing it in warm water so that it quickly thaws, the latter 

 is immediately and deeply tinged with red. The sudden 

 thawing of the water within the pores of the cell-mem- 

 brane has in fact so altered them, that they can no 

 longer prevent the diffusive tendency of the pigment. 

 (Sachs.) 



§4. 



MECHANICAL EFFECTS OF OSMOSE OST THE PLANT. 



The osmose of water from without into the cells of the 

 plant, whether occurring on the root-surface, in the 

 buds, or at any intermediate point where chemical 

 changes are going on, cannot fail to exercise a great me- 

 chanical influence on the phenomena of growth. Root- 

 action, for example, being, as we have seen, often suffi- 

 cient to overcome a considerable hydrostatic pressure, 

 might naturally be expected to accelerate the develop- 

 ment of buds and young foliage, especially since, as com- 

 mon observation shows, it operates in perennial plants, 

 as the maple and grape-vine, most energetically at the 

 season when the issue of foliage takes place. Experi- 

 ment demonstrates this to be the fact. 



If a twig be cut from a tree in winter and be placed in a 

 room having a summer temperature, the buds, before dor- 



