696 
Journal of Agricultural Research voi. xxvii. No. 9 
During the year 1923, 378 plates were poured. These plates were made 
from 23 different lots of material and included 38 sets. Previous to 
1923, during the years 1909 to 1922, inclusive, there were 120 plates 
poured from apple stem-tumors, 12 sets from 9 different lots of material. 
No single colony of Bacterium tumefaciens appeared. There were some 
fairly constant bacterial colonies closely resembling crowngall colonies 
which appeared on the plates and these were tried out in 1923 on Early 
Harvest apple trees, a variety known to be susceptible to this disease. 
The trees were inoculated in May in 138 young growing stems, using 8 
different colonies; controls were held at the same time and the inocula¬ 
tions were made in two orchards 18 miles apart. The following green¬ 
house plants, known to be susceptible to Bad. tumefaciens , were also 
inoculated with these 8 colonies: 30 Paris daisies, 31 young tomato 
plants, 16 Ricinus, 12 Bryophyllums, 5 tobacco plants and 6 geraniums. 
The results with these plants were all negative. 
In the case of the apple trees under observation, swellings occurred in 
the axils of leaves of branches where there were neither inoculations nor 
contrpl pricks. These swellings were small; even as late as October they 
were only 3 mm. to 1 cm. in diameter. Five swellings which occurred on 
the main stem of a young tree were much larger; these varied from 1 to 
2j^ cm. in diameter. The large outgrowths had the typical budlike 
projections of apple stem-tumor. These places were not inoculated nor 
were any places on the main stem of the tree inoculated. The only stimu¬ 
lating ageilt present in October which might be held responsible was the 
woolly apple aphis (.Erisoma lanigera Hausmann) a colony of which was 
on each of these swellings. The tumors had been noted in July when they 
were smaller, and the aphis was also on them at that time. These tumors 
were so fresh and soft that the writer, thinking it might be a natural in¬ 
fection of crowngall, cut off portions of two of them expecting to isolate 
the crowngall organism very readily from these pieces. It could not be 
done. 
Woolly aphids were in the axils of the leaves where axil swellings 
occurred (PI. 3, A). The inoculated places were carefully examined and 
in all of the 138 inoculated stems there were only three outgrowths. 
These three places were in the axils of leaves and were covered with 
woolly aphids. Some of the small axil swellings on these Early Har¬ 
vest apple trees were cut off, and also pieces of the large stem-tumors, 
a second time. Platings were made from both lots but neither the 
crowngall nor any other constant organism appeared on the plates. 
In an orchard where stem-tumors were quite prevalent 44 trees were 
examined at the roots and woolly aphis root galls found on 34 of them; 
32 of these rootgalled trees had stem-tumors, and only one tree was 
found with stem-tumors which did not also have the aphis rootgalls. 
On the roots of one of the trees most severely affected with stem- 
tumor the woolly aphis was present in great numbers and had produced 
root-tumors (PI. 3, C). The same insects were present on the branches 
also and were abundant on the sterna tumors (PI. 3, D). No crowngall 
was found on any of the trees. 
Not all varieties of apple trees appear to be subject to these stem- 
tumors. The character of the soil and cultivation may have much to do 
with this, but some varieties, as the Early Harvest, seem susceptible 
under any conditions. Very susceptible varieties which have come under 
the observation of the writer are the following: Early Harvest, Wagoner, 
