138 PLANT PROPAGATION 



In graftage of mature wood such a blending is impos- 

 sible ; for with the exception of the cambium layer both 

 stock and cion consist almost wholly of dead heart wood 

 and dead bark which cannot unite with anything. 



It is different to say the cambium layers of stock and 

 cion unite. But even this statement does not explain 



FIG. 122 SECTION OF APPLE GRAFTS 

 1. Transverse section. 2. Longitudinal. 



the process, though it leads in the right direction, for the 

 cambium and a few layers of cells on each side of it are 

 the only part of an exogenous stem really alive. Upon 

 it depends the possibility of a graft union. 



Even naked eye examination of cross or transverse 

 sections of successful grafts several years old will show 

 (1) that cion and stock have not united and (2) that 

 wood produced after the union is as continuous as in an 

 ungrafted stem. At least in the layers that bury a graft 

 junction whatever difference there may be is not appar- 

 ent. The truth of the diagram (Fig. 121) is fully sup- 



