GRAFTS. 269 



Grafted plants are apparently very much ex- 

 posed to injury by slugs, insects, and the invasions 

 of parasites during the healing of the callus and 

 the fusion process. Here again it must not be 

 overlooked that the callus is, so to speak, a tit-bit 

 of luscious, thin-walled, succulent tissue ; and, like 

 all wounds, the graft affords entrance to parasites 

 such as Nectria and Ascomycetes of various kinds, 

 under circumstances very favourable to their in- 

 vasion. 



Natural Grafts. It is by no means an un- 

 common event to find the branches of Beeches, 

 Limes, and other trees which have been acci- 

 dentally brought into contact during growth, 

 joined where they cross. As they press one 

 against the other, they become naturally grafted, 

 by that form of the process known as inarching : 

 except that in artificial inarching the operator 

 cuts off the cortical tissues of the two branches 

 and brings their cambial surfaces together, whereas 

 in nature the cambiums only come into con- 

 tact after the destruction by pressure, or slight 

 abrasion, of the entrapped intervening tissues. 

 The fusion occurs, in fact, exactly as in the 

 burying-in of a nail or wire, referred to on p. 211. 



Natural grafts are very common among the 

 roots of trees, and possibly explain some queer 

 cases of the apparent revivification of stumps of 

 trees not usually given to forming abundant stool 

 shoots. It is regarded as probable in some old 

 forests that the majority of the roots of trees of 

 the same species are linked up together by such 



