Wormald . — 'Brown Rot 9 Diseases of Fruit Trees. 389 
(d) Apple Flowers inoculated with Strains of Monilia cinerea. 
In the course of the investigation of the ‘ Wither Tip ’ disease of plum 
trees it was discovered that two morphologically similar strains of Monilia 
cinerea had the power to infect apple flowers in different degrees of inten- 
sity. A strain obtained from a diseased plum twig, although it was able to 
induce withering of the actual flowers inoculated, was unable to proceed 
beyond the base of these, and the rest of the flowers of the same inflores- 
cence were not affected, while a strain obtained from an apple spur not 
only readily infected apple flowers but invaded the tissues of the axis of 
the inflorescence and caused a wilting of all the flowers and leaves borne on 
that axis (Figs. 10 and 11). These results suggested the occurrence of 
‘ Biologic Forms 5 within the species Monilia cinerea ; for confirmation of 
this conclusion further experiments were carried out in 1918, using other 
strains of M. cinerea. 
One of the strains selected had been isolated from a tree of Pyrus 
japonica which was affected with a Blossom Wilt resembling that of the 
apple. This strain, though obtained from a species of the same genus as the 
apple, showed certain physiological characters similar to those of strains 
isolated from species of Prunus. It had been isolated from a wilted flower 
in July, 1917, and when used for inoculations had been cultivated saprophy- 
tically on artificially prepared media for ten months. In the experiment in 
which it was used, a strain obtained from an apple spur in March, 1917, was 
taken for comparison. 
The first experiment of the series was carried out with one strain of the 
apple form of Monilia cinerea originally isolated from a ‘ Brown Rot ’ Canker 
in 1916, but re-isolated in 1917 and again in 1918 from an apple spur which 
had been infected after artificial inoculation of a flower with a pure culture 
in 1916. Thus in 1918 the original and two sub-strains were available for 
the experiment, viz. (1) the original strain which had been growing on 
artificial media for two years, (2) sub-strain grown for about twelve months 
artificially, (3) sub-strain isolated a few weeks previous to the inoculations. 
The experiment was carried out with the object of ascertaining whether the 
form of M. cinerea which causes the Blossom Wilt of apples retains its 
virulence after continued culture on artificially prepared media. 
The strains used in this series of experiments on apple flowers were 
from various sources and hosts as shown below : 
Strain A r — Isolated in April 1916 from a ‘Brown Rot 5 Canker of 
a Cox’s Orange Pippin apple tree (specimen sent from Berkshire), 
and afterwards cultivated in pure cultures in the laboratory. 
Strain A 2 . — Isolated in March 1917 from an apple spur which had 
become infected in the College plantation after artificial inocula- 
tion in 1916 with a pure culture of Strain A r 
