304 VEGETABLE ORGANOGRAPHY. 



shall here briefly examine the means -by which the use 

 of leaves is supplied, wholly or in part, when they 

 happen to be wanting either naturally or accidentally. 



When the leaves are accidentally wanting at the 

 period when their presence is necessary, as, for example, 

 if for any particular purpose they are stripped off" a 

 tree when it is in a growing state, as is done to the 

 Mulberry ; or if the hail destroy all of them, when 

 the tree is in full growth; a vital phenomenon ensues, 

 which partly repairs the injury. All the latent buds in 

 the axils, which would not have been developed till the 

 following year, grow very rapidly, and form new leaves ; 

 if, by any particular circumstance, this phenomenon 

 does not take place, the tree usually perishes. 



Plants deprived of leaves by their own organization, 

 deserve to be examined more in detail, as it refers 

 entirely to Organography. It may be said, in general, 

 that when a plant is naturally devoid of leaves, the use 

 of these organs is supplied by some other organ of the 

 same plant, or by another plant. 



The absence or diminution of the limb is supplied : — 



1st. By the dilatation of the petiole, the fibres of which 

 spread out and separate sufficiently to permit the de- 

 velopment of cellular tissue and the opening of stomata ; 

 this is observed in the highest degree in almost all 

 leaves without limbs. 



2d. The foliaceous limb is also suppKed sometimes by 

 the stipules, which are the more developed the more 

 completely the limb is devoid of leaflets, as is seen in 

 Lathyrus Aphaca. 



3d. In several plants in which the leaves are either 

 totally wanting, or are very small, or fall off" very early, 

 the surface of the bark of the young branches, which, in 

 the ordinary state, is a parenchyma, very analogous to 

 that of leaves, performs entirely the function of those 



