GRAFTING 77 



such a distance that it was difficult to find uninjured 

 bark for doing root grafting. The old scars appar- 

 ently represented many winters of feeding of field 

 mice. Several fungi, notably armillaria, attack the 

 roots of the Persian walnut in a destructive way, but 

 the black walnut root has a high degree of immunity 

 to attacks of fungi. 



The question of choice of stock is something to 

 be developed gradually through experience. An ob- 

 ject lesson consisted in an experiment in top-working 

 two hickory trees situated only a few yards apart; 

 each about thirty feet high. One was a bitternut, 

 the other a smooth-bark pignut. All of the branches 

 of both with the exception of a top branch were cut 

 off and the stubs grafted with Beaver hybrid on 

 June fifteenth. Practically every one of the grafts 

 placed on the bitternut stock made exceptional 

 growth. Almost every one of the grafts set upon 

 the pignut started to grow and then all died back 

 when they were less than three inches in length. This 

 indicates that the bitternut was an excellent stock 

 and the pignut a very poor one for top working 

 with this particular hybrid (a cross between the bit- 

 ternut and shagbark). The Beaver hybrid grafted 

 upon shagbark does very well, but chooses by pref- 

 erence its bitternut ancestor. In the case of the 

 Beaver hybrid just quoted caprice was shown. It 

 was accepted eagerly by a host representing one of 

 its parents. It was refused as a guest by the pignut 

 which did not represent either one of its parents. 

 The pignut stock, however, would have accepted 



