182 VEGETABLE ORGANOGRAPHY. 



from the buds. I do not deny, however, that the buds, 

 or rather the leaves which they produce, have some influ- 

 ence upon the formation of the wood ; but it is an action 

 which appears to me to be purely physiological ; they 

 elaborate the descending sap ; and we know from this 

 that the more buds or leaves there are in the upper part 

 of the tree, the more the young wood is nourished. 

 Thus, whilst Du Petit-Thouars attributes to the buds 

 the origin of the fibres, and to the alburnum and liber 

 their nutrition, I am of opinion that the leaves produce 

 the nourishment, and that the fibres are developed by 

 the liber and alburnum. 



Turpin has modified the opinion of Du Petit-Thouars, 

 in admitting two classes of fibres ; one of which de- 

 scends' from the aerial buds towards the roots ; whilst 

 the others arise from the extremities of the roots, and 

 go in a contrary direction to the preceding. He thinks 

 that each of these two systems of fibres is prolonged as 

 long as the contrary one does not meet with any ob- 

 stacle : this explains, according to him, how, in the case 

 of the dissimilar graft, of which I have lately spoken, 

 the lower part of the trunk remains of the same nature 

 as it originally was ; but in this theory we cannot under- 

 stand either how the roots can give nourishment to the 

 ascending fibres, the existence of which is not demon- 

 strated ; or how these fibres, which are supposed to 

 spring from the roots, can take a nature and properties 

 so different in passing the neck. 



All other naturalists, although there is little accord- 

 ance between them, are agreed at least upon this 

 point, — that the formation of the new woody and cortical 

 layers is produced at the point of contact of the two 

 systems, and ought to be considered in the horizontal, 

 and not in the vertical direction. A very simple fact 

 demonstrates this proposition : If a tree, which has been 



