16 FIELD STUDIES OF THE CROWN-GALL OF THE GRAPE. 



number of instances at the age of from 10 to 12 3 r ears. Some varieties 

 of Vitis aestivalis, such as Herbemont, appear to be immune to the 

 disease. 



Vines of Vitis cordifolia and V. linsecomii purchased from a nursery 

 were found badly diseased with crown-gall, indicating a suscepti- 

 bility of these species to the disease. 



Vines of varieties of Vitis rupestris and V. vulpina, so far as 

 observed, are apparently quite resistant, in fact almost immune to the 

 disease; for example, Rupestris St. George and Rupestris Martin. 



THE SUSCEPTIBILITY OF VARIETIES OF EUROPEAN GRAPES. 



All the data collected from experiments and observation indicate 

 that there is a great range of variation in susceptibility of the varieties 

 of any given species to the disease. 



Of the varieties diseased to the greatest extent in any given locality 

 it was observed in general that those most easily injured by late spring 

 frosts are most susceptible to the disease. There are probably some 

 exceptions to this rule, since the disease is able to gain an entrance 

 into the tissues of vines through wounds without the action of frost. 



The varieties of Vitis vinifera that were found in the experiments 

 most susceptible to the disease were the Mission from California, 

 Muscat of Alexandria, .„ Flame Tokay, Rose of Peru, and Malaga 

 varieties. There are no doubt others not included in the experiments 

 that are equally susceptible. 



At Bernalillo, N. Mex., an experimental vineyard for the study of 

 the disease has been conducted since 1903. The vineyard originally 

 contained vines of the Mission variety from California, badly dis- 

 eased with crown-gall at the age of 4 years (PI. I). These vines 

 were first treated in various ways in an attempt to control the crown- 

 gall, but without success. The diseased vines were then replaced 

 chiefly with other varieties of Vitis vinifera in an effort to obtain 

 resistant vines. A number of the best varieties of commercial wine 

 and table grapes grown on their own roots, purchased in California, 

 were set in the holes from which the diseased Mission grapes had been 

 removed (PL IV, fig. 1). This put the new vines to an exact and 

 extreme test, since each vine was planted in infected soil. 



The vines of some varieties became badly diseased in two years and 

 were replaced at the end of the second year with more resistant varie- 

 ties. The following table presents the result of the experiment to 

 July 1, 1909: 

 is:? 



