540 
Journal of Agricultural Research 
Vol. XXX, No. 6 
Conidia of Venturia inaequalis were 
found in the air only during rain 
periods, and particularly when rain 
was accompanied by strong wind. 
Experiments showed that these conidia 
are very resistant to detachment 
from their conidiophores when dry, 
but quickly become detached in the 
presence of water. They are, there¬ 
fore, disseminated chiefly in meteoric 
water acting under the influence of 
wind and gravitation. 
Germination tests showed that prac¬ 
tically all naturally discharged asco- 
spores were vigorously viable. Conidia 
germinated with much less regularity. 
At no time after their appearance in 
the spring, however, was it difficult to 
find viable conidia in abundance. 
The seasonal development of the host 
plant was unusually slow in the spring 
of 1917. In the Turville orchard most 
of the blossoms were open by May 18, and 
petal-fall was about complete on May 25. 
The last leaves to develop appeared 
from about May 19 to 24, and very little 
leaf expansion occurred after June 8. 
Bagging experiments and orchard ob¬ 
servations showed that most of the leaf 
infection of the season occurred during 
the period of May 19 to June 2, during 
which time all but one of the major 
ascospore discharges of the season oc¬ 
curred. The first observation of leaf 
lesions was made on June 2, 14 days 
after the first period of ascospore dis¬ 
charge. As the leaves approached ma¬ 
turity they became highly resistant to 
infection by the scab fungus. 
Fruit infections were observed on 
June 8 and continued to appear 
throughout the period of observation, 
which ended on August 24. The rec¬ 
ords indicate that the first fruit infec¬ 
tion occurred during the rainy period 
of May 19 to 23. 
Successful leaf inoculation experi¬ 
ments were conducted in the orchard 
upon branches inclosed in specially 
constructed moist chambers. Infec¬ 
tion from conidia applied in suspension 
in water was secured at will upon young 
leaves if fairly low temperatures (maxi¬ 
mum at which infection occurred some¬ 
what above 25°C.) were maintained. 
Old leaves were highly resistant to in¬ 
fection by Venturia inaequalis . 
