836 



zone of the bud represents an integral part of this. The zone (cc), if traced 

 backward, is found to be a direct prolongation of the cambial ring of the 

 uninjured axial part. 



If the wound is closed by the coalescence of the different wound tissues 

 and the union of their cambial zones, the thin-walled tissue of the wound 

 callus (ok) has almost disappeared and has been replaced by actual uniting 

 tissue in which groups of porous cells may be often distinguished from less 

 porous ones, as mentioned above. As indicated by the bark tip (-?-j) the 

 wood parenchyma, which takes over the formation of a permanent union, is 

 also produced directly and in fact in the angles where the bark strip and 

 wood body join, i. e. where the indicating line from kg ends. When it is 

 perceived that the bark strips {3 R L) have been so raised by the budding 

 knife, that not only the whole cambial zone but also the young sap wood 

 elements already differentiated remain attached to them, then it is evident 

 that this connecting tissue is a product of sapwood cells already somewhat 

 older (not those most recently formed). This tissue is not produced from 

 the wound callus (which is never formed in the inner angles) but from the 

 division of cells already destined to be wood cells and vessels. 



We have, therefore, three different factors which furnish a similar 

 product, the wood parenchyma, already described as the uniting tissue, 

 which takes over the process of uniting scion aiid stock. The first factor is 

 the bark strip from the stock, the second the callus of the exposed wood 

 body, the third the scion. The momentary strength of the different factors 

 determines which one of these three actually produces the union in a grow- 

 ing graft or bud. The variations w^hich may be observed are extraordi- 

 narily great. The quickest possible formation of wound callus, which takes 

 over the temporary closing of the wound, is essential for the success of the 

 graft. However, the union becomes permanent only if the cambial zone 

 {cc) of the strips (R L) which forms the new wood and which I have 

 occasionally called "the mobile wound-wall" occurs in permanent union with 

 the cambial zone (c) of the scion (or bud) and forms wood elements 

 remaining in a connected layer. The mobile wound-wall shows the charac- 

 ter of the usual overgrowth edge by its cambial zone which is spirally 

 twisted on the free side, and distinguished from this overgrowth edge, the 

 "fixed wound-wall," by the large, inpushed zone of wood parenchyma (kg), 

 which passes out from the fixed wound-wall. The point of union of the 

 cambial zones of stock and scion (or bud) is recognizable not only in the 

 year of the union but remains so for many years, by the course of the wood 

 elements. In the line of union, which extends from c to cc, the elements 

 are more or less strongly elongated tangentially, while in the interior of the 

 wound-wall they have already assumed the normal vertical arrangement 

 and, therefore, in cross section appear actually cut across (hh'), thus resem- 

 bling the normal wood (hh). If, in the production of this uniting tissue, 

 the cambial zone (c) of the scion (or bud) unites with that of the stock (cc) 

 to form a continuous ring, it is evident that this ring is not everywhere 



