GRAFTING 79 



but the farther removed the stock is from the graft- 

 ing varieties the less success we have on general 

 principles. This is doubtless due to the fact that 

 the food supply required for root and top is most 

 satisfactorily elaborated by roots and tops closely 

 allied. The Japanese sometimes graft widely sepa- 

 rated species successfully, but we do not as yet know 

 the limitations. I have grafted chestnuts on several 

 species of oaks and have had them grow thriftily on 

 red oak for two years, but the structure of the wood 

 of the chestnuts and oaks is so different in character 

 that firm ligneous union does not seem to occur and 

 grafts are readily blown away in a heavy wind. 

 Chestnuts are prone to make incomplete woody 

 union even when grafted upon closely allied varieties 

 and species of chestnuts. I top worked a Chinese 

 chestnut tree with grafts of the American sweet 

 chestnut on one occasion and during the early part 

 of the season the American chestnut grafts made 

 tremendous growth; shoots several feet in length in 

 some cases. All at once these began to wilt back 

 without known cause. I found on making sections 

 for microscopic examination that union was not suf- 

 ficient between graft and stock. The callus had al- 

 lowed very rapid development of the shoots up to a 

 certain point and then refused to grow them further. 

 There were four exceptions among the grafts on this 

 tree. On examining these four grafts which re- 

 mained thrifty I found that some insect had injured 

 the terminal bud when the shoots were less than a 

 foot in length and the scion had to wait in this case 



