534 CASUALTIES OF VEGETABLES. CHAP. XII. 



species of serpents, which may be regarded as a 

 distinct organ. But although the skin of the snake 

 or of any other animal may be regarded as a distinct 

 organ, yet it must be in a light very different from 

 that of an organ attached to the body of a plant or 

 animal by a natural joint or articulation that comes 

 asunder of its own accord; for the skin of the animal 

 in question is forced off in the manner of a slough 

 merely by means of the formation of a new skin be- 

 neath it, which has already taken the place of the 

 old skin in the living system, and to which it has 

 just been shown that there exists nothing whatever 

 analogous in the fall of the leaf. So that, after all, the 

 best reason we can give is, perhaps, that the leaves 

 fall in consequence of their being worn out, and no 

 longer necessary to the immediate process of vege- 

 tation ; which is evidently divisible into animal 

 stages commencing with the approach of spring, 

 and terminating with the return of winter, which 

 is to the vital principle, apparently, a period of rest. 

 If it is necessary, however, to attempt an explica- 

 tion of the process by which the leaf is made ulti- 

 mately to detach itself from the plant, it may be 

 observed that it consists wholly in the change that 

 is effected in the articulation uniting the foot-stalk 

 to the branch, as is evident from the remarks of Mr. 

 Fairburn ; for in the case in which the injury ex- 

 tends suddenly beyond the leaf, the leaf may wither 

 and decay, but will not fall off, because the articula- 

 tion has not been duly prepared, and because the 



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