SUSCEPTIBILITY OF VARIETIES OF APPLE TREES. 43 
a doubt as to whether the variety called ‘‘Martha”’ used in the experi- 
ment was true to name. Of the slow-growing varieties, the Yellow 
Transparent showed an average of 34 per cent of diseased trees, the 
Maiden Blush 26.4 per cent, and the Whitney 20.4 per cent. It must 
be concluded that susceptibility is not directly related to vigor of 
erowth. 
It was found that those varieties that throw out roots more readily 
from the scion are the ones that are most susceptible to hairy-root. 
The forms of hairy-root apparently originate only in tissue centers 
capable of producing adventitious roots. 
SUSCEPTIBILITY OF SCIONS GROWN IN DIFFERENT LOCALITIES. 
The collection of data on the susceptibility of different varieties of 
apple trees to crown-gall and hairy-root brought out the fact that 
while certain varieties were found to be more susceptible than others, 
the same variety during the same season or several seasons was dis- 
eased more in one locality than in others. This could probably be due 
to a number of facts, one of which might be a varying susceptibility 
in stocks of the same variety grown in different localities. 
To ascertain whether there was any difference in susceptibility of 
stocks in different sections of the country, scions of three different 
varieties of trees were obtained from a number of nurseries from Ohio 
to California. These varieties were Wealthy, Wolf River, and Yellow 
Transparent. Each variety was made into root grafts, the same stock 
of seedlings being used. They were planted in 1906, each variety in 
a different plat, and grown three years before digging. The names of 
the nurseries furnishing the scions are not given, numbers being sub- 
stituted, but the State in which each nursery is located is given. 
Table XXII, in the appendix, gives the number of trees grown from 
each lot and the percentage diseased. 
From the results given in the table it will be seen that there was 
a great variation in the amount of disease present in scions taken 
from different localities, but it will not be safe to ascribe this wholly to 
sreater susceptibility, since the health of the trees from which the 
scions were selected in each locality could not be ascertained, and it 
has already been shown that this is a factor in the problem. 
The difference in the percentage of disease in the case of the Wolf 
River variety, as shown by the two extremes in the results from the 
experiment, is 14.7 percent. In the experiment with the Wealthy itis 
17.5 per cent, and with the Yellow Transparent 12.8 per cent. This 
is quite a wide range, but since the results can not be considered as 
strictly comparative they may be taken as tentative, paving the way 
for further inquiry along this line. 
186 
