308 W or maid. — Further Studies of the Frown Rot ’ Fungi. I. 
xylem produced during the season in which infection occurred (Plate XIV, 
Fig. n). 
Although pustules of Monilia cinerea may develop on the dead leaves 
during wet weather in the summer, they are not found on the bark of the 
shoots or on the cankers until winter approaches. Early in December 
Monilia fructifications were seen on the bark of a number of the dead shoots 
and on the petioles of the withered leaves. Conidial fructifications con- 
tinue to develop during the winter months, and in February nearly all the 
cankers labelled in June of the previous year bore grey conidial tufts, usually 
at the base of the short shoots, but also frequently on the bark of the cankers. 
The cankers by this time were, in many cases, nearly covered with callus, 
which, developing from the two sides, had almost reached the middle line 
and had caused the bark to become ruptured (Plate XIII, Figs. 3 and 4). 
The conidia produced on the Monilia pustules of the cankers during 
winter and spring have dimensions similar to those of M. cinerea found on 
the mummied fruit and on withered tips at that time of the year. Conidia 
taken from a pustule growing from a canker in March showed variation in 
size from 7*5 x 5*5 /u, to 16 x 11-5 /x ; they were mostly, however, within the 
range 10-12*5 x 7 — 9*5 and the average of 100 conidia was 11*3 x 8*4 /x. 
The conidia produced on the young leaves in summer are larger than 
those of the cankers, their size being of the same order as that of the 
‘ summer conidia * of the fruit. 1 
Although the wilting of the short shoots of the plum trees had not 
been observed previous to the spring of 1919, or if noticed had not been 
recognized as a ‘ Brown Rot ’ disease, there was evidence that it had 
occurred during the seasons 1918 and 1917 on some of the trees examined, 
for certain cankers were found (in 1919) which from their condition and 
their position on the branches indicated that infection had taken place 
through the short shoots. Thus on two-year-old wood there were cankers 
at nodes where there must have been short leafy shoots during the previous 
year. These cankers were partly covered by callus and almost invariably 
bore pustules on the short dead shoots or on the cankers ; they correspond 
to, and were similar to, those cankers which were kept under observation 
and found to produce pustules during the season subsequent to infection. 
Somewhat similar cankers, but with callus further developed and bearing no 
pustules (most of the dead bark having peeled away), were found on the 
three-year-old wood ; these were evidently a further stage in the formation 
and the healing over of the Shoot-Wilt cankers (Plate XIV, Fig. 7). 
II. Isolation and Cultural Experiments. 
Pure cultures of Sclerotinia cinerea could easily be obtained from the 
mycelium found in the tissues of the young cankers. The surface of 
1 See p. 315. 
