Worm aid.- — ‘ Brown Rot ’ Diseases of Fruit Trees. 383 
by M. cinerea , the maximum extension for the former being 12 mm. and 
for the latter 9 mm. The brown colour on the fruit-stalk extended 
upwards from the point of insertion on the plum, indicating that the 
disease was advancing from the fruit, along the stalk, towards the branch. 
The pustules of M.fructigena were to 1*5 mm. in diameter, usually about 
1 mm., and their colour was ‘ Light Buff’ of Ridgway’s colour charts; 1 
those of M. cinerea were conspicuously smaller, reaching a maximum diameter 
of o*8 mm., the usual diameter being about 0-4 mm., and their colour was 
‘ Smoke Grey ’ to { Light Greyish Olive \ 
On July 27 plums Nos. 2 f and 2 c were removed from the tree and 
photographed, together with a sound plum from the same tree (Fig. 8) ; 
the plum No. 6 was also photographed on the same day (Fig. 9). 
The results obtained in this experiment prove conclusively that 
M. fructigena and M. cinerea are equally able to cause a 5 Brown Rot ’ of 
plums, and that under these conditions the two species are morphologically 
quite distinct, as shown by their fructifications. 
Experiment 2. 
The experiment recorded here is one of a series carried out with the 
object of ascertaining whether the two forms mali and pruni of Monilia 
cinerea could be distinguished when growing on plums. The experiments 
were suggested by the fact that of all the strains of M. cinerea obtained 
from plums or cherries (more than 20 in all), not one could be identified, by 
the characters given later in this paper, 2 as forma mali, and a reason was 
sought for this absence of the apple form from species of Primus. M. cinerea 
f. mali produces pustules less freely on sterilized potato and on apples (as 
shown in preceding pages) than f. pruni , and it was thought that the former, 
if it did occur occasionally on plums, was unable to become established 
there, for experiments on apples in the open showed that pustules were 
necessary for the diseased fruit to be retained on the trees as mummies. 
Preliminary experiments in the laboratory proved that the form mali grows 
readily when inoculated into picked plums, again with a tendency to develop 
fewer pustules than does the form pruni. 
During the summer of 1918 plums growing in the College plantation 
were inoculated on June 21, June 24, and July 15 ; on each occasion the 
strains used were : 
M. cinerea forma mali, strain from a 6 Brown Rot Canker \ 
,, ,, mali, „ „ an apple spur. 
„ ,, pruni, ,, „ a mummied plum. 
„ „ pruni , ,3 „ a mummied cherry. 
1 Color Standards and Nomenclature. Washington, 1912. 
2 These features will be discussed in Part II of this paper. 
