SECT. II. THE STEM. 277 



times the bark of the stem becomes rough and 

 scabby and the wood underneath full of knots and 

 inequalities, this Du Hamel attributes to frost also. 



Sometimes two or more contiguous stems, extend- The fasci- 

 ing in the process of their growth till they meet s tem. 

 and press against one another, become incorporated 

 at length into one, and form a sort of bundle. This 

 is what may be termed a natural graft, in opposition 

 to an artificial graft, of which it is the model and 

 prototype, the whole of the art of grafting being 

 founded upon the capacity inherent in plants of 

 uniting together by the stem, in given circum- 

 stances, and in a given mode. But the natural 

 graft is always affected by means of the union of 

 the liber of the respective stems composing it ; so 

 that the perfection of the art of grafting consists in 

 applying the liber of the graft and stock together 

 in such a manner as shall the most facilitate their 

 incorporation. And hence the graft will not suc- 

 ceed unless the two libers are brought into contact, 

 and closely bound together. Nor will it succeed 

 well unless the plants ingrafted have some natural 

 affinity to one another, such as that subsisting be- 

 tween the Plum, and Cherry ; in which, and in all 

 other cases, the union is effected by means of a 

 granular and herbaceous substance exuding from 

 between the wood and bark, and binding and ce- 

 menting together the stock and graft ; though not 

 uniting the former layers of wood. But after the 

 graft has been effected, the new layers of wood arc 



