512 CASUALTIES OF VEGETABLES. CHAP. Xtl. 



ttiilar to that of the sloughing of diseased parts in 

 the animal economy. 



It does not, however, seem quite evident to me 

 that the idea of sloughing is comprehended in the 

 opinion of Vorlick, at least as represented by Will- 

 denow ; but if so, I do not think that the analogy 

 is very well made out. Sloughing, in the animal 

 economy, is that power or the exertion of that 

 power by which the vital principle is capable of 

 throwing off a part that has accidentally become 

 diseased and unfit for discharging the functions to 

 which it was originally destined ; but not that power 

 by which it is capable of throwing off a distinct 

 organ intended by nature to be finally separated 

 from the individual. Now in the case of the defo- 

 liation of the plant, there is, for the most part no 

 disease, but merely a gradual and natural decay 

 which reduces the leaf to a state, indeed, no 

 longer fit for the purposes of vegetation, but to 

 which it was intended by nature to be reduced for 

 the purpose of facilitating its separation from the 

 plant : and hence it always separates in a determi- 

 nate manner, and at a determinate point, namely, at 

 the base of the foot-stalk, which forms as it were a 

 sort of natural joint or articulation, to which there 

 is nothing analogous in the case of sloughing. If 

 this were not the fact, it might be expected that a 

 part of a leaf, or even the whole of it, should occasion- 

 ally become permanent, as well as the branches, 

 though no such thing has ever yet happened. 



