212 AMERICAN VINES. 



layers is transformed into a generative layer, knitting with 

 the generative layer of the scion. From this moment the 

 whole plant grows normally above, below, and at the knitting 

 point; and wood inside, liber outside, are formed in the 

 normal way. The cells produced by the other regions of the 

 liber and bark knit also, and become transformed, so as to re- 

 constitute the tissue from which they were derived. 



If the pads of callus are only brought in contact when 

 older, the knitting takes place under unfavorable conditions ; 

 it takes place, however, in the above-described manner, but 

 only after the external layers of corky cells have become trans- 

 formed and regenerated. 



The tissues resulting from the new generative layer get 

 differentiated, so as to form fibro-vascular bundles, or 

 medullary rays, etc., corresponding to those of the stock. 

 However, more or less numerous anastomoses, arranged in 

 the form of entangled network, are produced at the knitting 

 point. The channels of the wood and liber, newly formed at 

 the joint, are therefore in direct communication with those 

 of stock and scion ; the circulation of the sap takes place in 

 almost the same manner as in a non-grafted plant. 



If layers of the bark other than the generative layers inter- 

 vene in the formation of the joint, the part the latter play is 

 by far the most important. The generative layers must exist 

 in the knitting tissue to form the wood inside, which will 

 support the stem and liber outside. The joints in which the 

 liber alone knits (this sometimes happens), are of only 

 temporary duration, unless a generative layer forms to join 

 the generative layers of stock and scion together. We 

 know, as a matter of fact, that every year the liber of the 

 preceding year exfoliates, and becomes detached from the 

 cane in thongs, more or less thick, constituting what vine- 

 growers commonly call bark. 



Such is, roughly, the mechanism of knitting. 



In all that precedes, we have assumed that the stock was 

 a portion of cane more ,or less old. Roots, or portion of root, 

 if large enough, may also be used. Large vine roots have 

 (with the exception of a few liber fibres) practically the 

 same structure as a two or three years' old cane. The knitting 

 therefore takes place in the same manner. 



The healing or knitting tissue is not produced as readily 

 by all varieties, whether used as stock or scion. This also 

 applies to many other plants. Some produce no or very 



