Wormald. — ‘ Brown Rot ’ Diseases of Fruit Trees . //. 163 
while on recently infected fruit^n summer the average length is 
about 17 jut. 
M. fructigena produces conidia freely only in summer and autumn, and 
their average length is from 20 fx to 24*5 jut, according to the conditions 
under which they are produced. 
(c) Viability of the Conidia . 
During the winter months the pustules of Monilia fructigena are, as 
a rule, barren, as the conidia are mostly dispersed by the wind or washed 
away by rain in the autumn, and no others are produced until the approach of 
summer ; those conidia still adhering to the pustules in winter are generally 
found to be collapsed or shrunken and incapable of germination, although 
particles of the pustules themselves, when placed in hanging drops of distilled 
water or on culture media, readily develop hyphae within 24 hours. 
These barren pustules differ in general appearance. Some are non- 
pulverulent ; these vary in colour from a pale straw colour to almost white. 
Others are somewhat pulverulent or velutinous and are dark brown in 
colour ; this condition is due to the presence of a hyphomycetous fungus with 
brown mycelium and conidia growing on the old pustules of M. fructigena 
(see Fig. 3). 
On the other hand M. cinerea is stimulated to the production of pustules 
and conidia during winter. The form which produces the Blossom Wilt of 
apple trees, when it invades the tissues of the flowers, flowering spurs, and 
branches, may produce pustules on the pedicels and floral organs of the 
attacked flowers soon after infection, but this is not invariably the case, and, 
in so far as the author’s experience has gone, appears to be the exception. 
Generally no pustules appear on the affected organs until about the beginning 
of December, when pustules begin to burst through the bark of the cankers and 
diseased spurs, and they continue to develop throughout the winter and 
spring. This condition, too, obtains in the young vegetative shoots of the 
plum when attacked by M. cinerea ; conidia may be produced on the 
affected leaves, but pustules do not appear at the surface of the axis of 
the shoot until the approach of winter. 
When M. cinerea occurs on fruit, e. g. plums and cherries, numerous 
pustules are produced during the summer (PI. IV, Fig. 1), and, persisting on 
the mummified fruit, redevelop and become pulverulent during the following 
winter and spring (Fig. 2). 
Apples which had been artificially inoculated with the apple Blossom 
Wilt form of M. cinerea in the laboratory produced no pustules, or very few, 
under those conditions, but when the infected black apples resulting from 
such inoculations were placed in the open air pustules burst through the 
skin and became covered with conidia during the winter. 
Conidia produced at these low temperatures germinate readily when 
