964 
Journal of Agricultural Research 
Vol. XXXI, No, 10 
Table IV. — Results of artificial inoculations in 1924, on seedlings of Prunus 
umbellata ( S . P. I. 38974) 
Number 
of seed¬ 
lings 
Age 
(years) 
Number 
of inocu¬ 
lations 
Number 
of galls 
Per cent 
of infec¬ 
tion 
1 
3 
90 
0 
0.0 
1 
3 
90 
2 
2.2 
1 
3 
110 
3 
2.7 
1 
2 
60 
5 
8.3 
1 
2 
60 
5 
8.3 
1 
2 
60 
5 
8.3 
1 
3 
70 
9 
12.8 
1 
3 
80 
23 
28.7 
1 
3 
80 
28 
35.0 
1 
3 
110 
44 
40.0 
1 
3 
100 
49 
49.0 
11 
910 
173 
« 19.0 
° Average. 
The seedlings whose inoculations are listed in Table IV were all 
growing vigorously, and were in favorable condition to give a high 
per cent of crown-gall infection. The seedlings showed considerable 
variation in their susceptibility, but in most cases they apparently 
were more susceptible than the parent tree. More than half of them 
(7) showed less than 16 per cent infection, and could well be listed 
with the resistant forms as given in Table III. The results suggest, 
at least, that with proper selection a resistant form of this species 
could be developed. An asexual method of propagation would of 
necessity have to be employed. From a limited test, the root¬ 
cutting method seems promising. 
The Japanese Apricot (Prunus mume) 
The species most thoroughly tested is the Japanese apricot, Prunus 
mume. The results of the tests are summarized in Table V. Two 
of the introductions, S. P. I. 28685 and 43558, were budded on other 
stock. The other three introductions were seedlings grown from 
pits imported through the Bureau of Plant Industry of the United 
States Department of Agriculture. The pits from S. P. I. 46694 and 
47950 were grown on the California Citrus Experiment Station 
grounds. S. P. I. 45523 consisted of 25 small trees obtained from 
the United States Department of Agriculture. It will be observed 
(Table V) that there is considerable variation in the percentage of 
galls that developed. S. P. I. 46694 is exceedingly low in this ratio, 
while S. P. I. 45523 is relatively high. The other three are practically 
alike. This variation in susceptibility can also be noted in the 
individual trees of introduction S. P. I. 45523. The trees of the 
other introductions are all practically alike in susceptibility, being 
very resistant. 
The galls that develop on the resistant trees of Prunus mume are 
small in size, sometimes mere pointlike growths that have formed 
on the healing tissue at the margin of the wound. These are usually 
less than one-sixteenth inch in height, with about the same diameter 
at the base. As to the shape, they are pointed rather than sub- 
globose. It is very probable that most of these smaller pointlike 
galls will not further increase in size. Resistance, while suggested 
