78 REASONS WHY OEGANS MAT GROW WITHOUT LEAVES. 



time exclusively in the cells of the green organs, the tubes and 

 vessels of the vegetable structure being mere recipients organ- 

 ized by the matters so elaborated. This power of assimilation 

 is believed to be owing to the high vitality of the cells of the 

 green organs; but in proportion as the subterranean parts 

 become organized their vital force increases, and at last it 

 becomes suf&cient to enable them to act independently of the 

 leaves or green parts. If, then, at the time when a subterranean 

 organ is cut off from communication with the leaves, its vitality 

 is sufficiently high, its cells not only absorb water and other 

 matters, as was the case from the beginning, but also decompose 

 and elaborate them, in the same way as the cells of the leaves. 

 The result of that elaboration is increase in bulk, partly 

 arising from the distension of the cells and the consolidation of 

 their contents, partly from the increase of the number of 

 the cells themselves, and also from filling the last formed 

 cells with the matter peculiar to the species. What is 

 required in order to secure increase in bulk is the power of 

 organization ; that power depends upon the presence of a 

 sufficient amount of vital force ; therefore, when a subterranean 

 body has gained enough vital force, it has gained all the 

 organic capabilities which are necessary for increase of size, or 

 growth, and is able to enlarge even though cut off from 

 communication with green organs. It must not however be 

 inferred that an underground organ will increase as rapidly 

 in the absence of leaves as it will if they are present. On the 

 contrary, m the latter case, it grows by virtue of its own vitality 

 and that of the leaves combined ; a double power is brought 

 to bear upon its increase, and at least twice as much food in 

 an organizable condition is presented to it for consumption. 

 All that we are justified in asserting is, that although leaves 

 may be gone, growth will go on— and to a much greater extent 

 than is supposed. If, then, a root-crop is from any accident 

 deprived of its leaves, it is by no means a necessary conse- 

 quence that the crop is arrested ia its growth ; on the contrary, 

 provided the defoliation does not occur till towards the end of 

 the season, growth will go on notwithstanding. 



It is to be observed that, as has already been stated, the 



