58 



ORGANOGRAPHY. 



BOOK I. 



petiole, the leaf itself, have all been remarked producing 

 them. On the leaf they usually proceed from the margin, as 

 in Malaxis paludosa, where they form minute granulations, 

 first determined to be buds by Henslow, or as in Bryophyl- 

 lum calycinum and Tellima grandiflora ; but they have been 

 seen by Turpin proceeding from the surface of the leaf of 

 Ornithogalum. (Fig. 18.) 



We are wholly unacquainted with the cause of the forma- 

 tion of leaf-buds ; all we know is. that they proceed exclu- 

 sively from cellular tissue ; and if produced on the stem, from 

 the mouths of medullary rays. It would seem as if certain 

 unknown forces were occasionally so exerted upon a bladder 

 as to stimulate it into a preternatural degree of activity, the 

 result of which is the production of vessels, and the formation of 

 a nucleus having the power of lengthening. There is, indeed, 

 an opinion, which I believe is that of Mr. Knight, that the 

 sap itself can at any time generate buds without any previously 

 formed rudiment ; and that they depend, not upon a specific 

 alteration of the arrangement of the vascular system, called 

 into action by particular circumstances, but upon a state of the 

 sap favourable to their creation. In proof of this it has been 

 said, that if a bud of the Prunus Pseudo-cerasus, or Chinese 

 Cherry, be inserted upon a cherry stock, it will grow freely, 

 and after a time will emit small roots from just above its 

 union with the stock ; at the time when these little roots are 

 formed, let the shoot be cut back to within a short dis- 

 tance of the stock, and the little roots will then, in conse- 

 quence of the great impulsion of sap into them, become 

 branches emitting leaves. 



