86 SYLVA AMERICANA. 



not appear to be 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 defoliation 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 determinate 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 occasionally become permanent, as well 

 as in the branches, though no such thing has ever yet happened. 

 And with the sloughing of the diseased part there is yet another 

 circumstance clashing with the analosr that is here instituted. 

 The part supplying the place of the slough, or throwing it off, is 

 formed or exists already formed immediately beneath it, and is 

 precisely of the same character with what the slough originally 

 was; which slough it pushes off as it comes itself to maturity, or 

 acquires strength sufficient for the effort. But the leaves fall off 

 when they have reached maturity of their own accord, without 

 being at all pushed off by the new ones, which are yet merely in 

 embryo, and do not even occupy the place of old leaves, but are 

 only formed contiguous to them, except in the case of the plane 

 tree, the new leaf of which is formed precisely under the base 

 of the foot stalk of the old leaf ; and yet we would not call the 

 fall of that leaf sloughing, because the new leaf does not after all 

 push off the old one ; and because there is here, as in other 

 cases, the same natural articulation uniting the leaf to the branch 

 or stem, and rendering it a distinct organ that is ultimately and 

 spontaneously to detach itself from the plant. Not that there 



