Wormald. — ‘ Brown Rot 9 Diseases of Fruit Trees, 381 
discoloration throughout the affected tissues, and another which develops 
few or no pustules and causes a discoloration which, primarily brown, 
gradually becomes darker in the superficial layers until eventually the whole 
surface is quite black. 
Growing apples infected with either species are far more easily 
detached from the tree than the sound fruit, unless they become attached 
to the bark, or to other apples in contact with them, by means of the 
pustules at the point of contact. This fact suggests a reason for the rare 
occurrence of M. cinerea . on apples, for the small and comparatively few 
pustules which it produces appear to be insufficient, to attach the fruit to 
the tree even should infection occur. The writer has occasionally found 
M. cinerea f. mali on the very young fruit, but never on any approaching 
maturity, even on trees severely attacked by the Blossom Wilt disease, 
while M. frnctigena , which usually develops numerous large pustules on 
maturing apples, is extremely common. 
Apples, when infected with a form which produces numerous pustules, 
soon become shrunken and wrinkled, while the skin of those infected with 
strains which do not develop pustules under those conditions often remains 
firm and smooth for some time after it has become quite black. The rapid 
desiccation of the tissues when pustules are present is probably due to two 
causes : (a) the rupture of the ep.idermis permitting evaporation from 
within ; (b) loss of water by reason of the respiratory and transpiratory 
processes in the cells of the hyphae and conidiophores of the pustules. 1 
(b) Plums inoculated with the Tzvo Species . 
These experiments were carried out in two series: (1) inoculations 
made with the object of comparing the morphology of the two species 
when growing on plums ; (2) inoculations with strains of Monilia cinerea 
for comparing results obtained with the form mali with those of the form 
pruni. 
The results obtained from inoculating growing plums with a ‘ Wither 
Tip ’ strain of M. cinerea have already been published ( 1918 ). A similar 
experiment was made about the same time, i. e. July 1917, using 
M. frnctigena ; the resulting brown rot was indistinguishable in general 
appearance from that produced by M. cinerea , but the pustules which 
developed were larger, and yellow in colour. Both species were able to 
cause infection of uninjured plums in contact with diseased ones by the 
development of modified pustules at the point of contact, a pad of hyphae 
being formed which was able to penetrate the skin. 
For confirmation of these results, and to obtain a more exact com- 
parison of the two when growing on plums, an experiment was started 
1 When apples bearing numerous M Ottilia pustules are placed in a closed glass vessel, moisture 
condenses on the internal surface of the vessel within a few hours. 
E e 2 
