450 
determine whether infection was as abundant 
under such a cover as in the open. Infection 
was fully as abundant. Conclusions could not 
be satisfactorily drawn, however, because it 
was found that the mesh of screen used was 
large enough under the conditions to allow 
the entrance of a large number of very small 
insects. The conditions of the experiment 
were, therefore, revised this year with the 
hope of making them crucial. Twelve-mesh 
wire screen cylinders, 15 cm. in diameter and 
30 em. long, were constructed to enclose parts 
of single branches. To prevent contact with 
the branches to ‘be enclosed, cords were run 
four times transversely through each cylinder. 
Some of the cylinders were slipped into closely 
fitting sleeves of fine bolting cloth (124 threads 
per linear inch). For durability, the bolting 
cloth was sewed into canvas which formed the 
ends of the sleeves, covering the rough ends of 
the wire, and extending past the wire about 
14 cm., sufficiently to permit secure tying. 
The ends of other cylinders were similarly cov- 
ered with canvas and the exposed part of the 
wire was painted with a mixture of tangle- 
foot and benzene. The cylinders were slipped 
over branches including either last year’s ter- 
minal shoots or bearing wood. In the former 
case the cylinders were extended far enough 
past the ends of the branches to allow for this 
year’s terminal growth. All this was done be- 
fore any of the blossoms opened, at the begin- 
ning of the pink-bud stage. The cylinders 
treated with tangle-foot were repainted fre- 
quently enough to maintain a sticky surface. 
No insects and no traces of them of any sort 
were found in any of the cages with one excep- 
tion.§ 
There were ten cylinders enclosing flowering 
wood. Flowers in two of these cages blighted, 
aS was shown by their appearance and as was 
verified by microscopic examination. The 
blight evidently entered through the calyx. 
Blossom blight was not abundant this season 
in this orchard. 
Forty cylinders, twenty of the bolting cloth 
8 One cylinder was accidentally allowed to dry. 
Two insects were found in it. The shoot was not 
blighted. 
SCIENCE 
[N. 8. Vou. XLVIII. No. 1244 
and twenty of the tangle-foot type, were used 
to include terminal growth. Of this year’s 
shoots four in the bolting cloth cylinders and 
eight in the tangle-foot cylinders blighted, a 
total of twelve in forty, or thirty per cent. 
This was practically the same proportion of 
blighted terminal shoots as prevailed among 
the unenclosed shoots, as was shown by a 
count of a thousand terminal shoots on these 
and adjacent trees of the same variety and 
age. 
From the above facts it appears that there 
must have been some agency of dispersal other 
than insects, and that insects were not even of 
primary importance as carriers. The only 
tenable hypothesis is that wind was the chief 
agent of transmission. Supporting evidence 
for this conclusion is found in two facts: (1) 
in the lack of insects in the orchard in suffi- 
cient numbers to account for the large amount 
of twig blight and (2) in the entire absence of 
insects from exuding cankers, whence they 
might receive their initial contamination. In 
three years’ close observation at blooming time 
one of the authors (Ruth) has not observed a 
single case of insect visitation to exuding cank- 
ers. Aphids were entirely absent through the 
season of floral and twig infection. Leaf- 
hoppers became evident in rather small num- 
bers only after the period of infection had 
passed. No other insects were present in suffi- 
cient numbers to be considered primary agents. 
F. L. STEvens, 
W. A. Ruty, 
C. S. Spooner 
UNIVERSITY OF ILLINOIS 
SCIENCE 
A Weekly Journal devoted to the Advancement of 
Science, publishing the official notices and pro- 
ceedings of the American Association for 
the Advancement of Science 
Published every Friday by 
THE SCIENCE PRESS 
LANCASTER, PA. GARRISON, N. Y. 
NEW YORK, N. Y. 
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