W or maid. — ‘ Brown Rot ’ Diseases of Fruit Trees. 373 
In this way purity of culture is ensured, for should contamination 
arise from fungus spores, or by bacteria capable of growing on the culture 
medium employed, it would be detected during the forty-eight hours suc- 
ceeding isolation, and should the sporeling be contaminated by bacteria 
which do not develop under those conditions and would therefore escape 
detection, they are eliminated by taking mycelium from the peripheral 
region of the mycelial disc after growth has proceeded for a few days. 
This method was the one adopted for obtaining the ‘ single spore strains ’ 
of Monilia frnctigena and M. cinerea (used in the experiments described 
in this paper) when viable oonidia were available, i. e. when the fungi were 
developing pulverulent pustules. 
When the parasites occur as barren mycelium in the tissues of the 
host they are induced to produce conidia on sterilized potato as already 
described in the papers on ‘ A Blossom Wilt and Canker of Apple Trees’ 1 
(1917) and ‘ A Wither Tip of Plum Trees’ 2 (1918). The conidia are then 
isolated and single spore strains obtained as described above. 
Single spore strains of Monilia fructigena were prepared directly from 
the conidia of fertile pustules on apples or apple spurs, or indirectly from 
barren pustules (winter condition) by placing particles of the pustules on 
the nutrient agar, thus inducing vegetative growth for sub-inoculation on 
potato for conidia production. ‘ Black Rot ’ strains of M. fructigena were 
also obtained indirectly by first stimulating vegetative development from 
particles of the diseased apple flesh (permeated with mycelium) placed on 
the agar. 3 
V. Inoculation Experiments with Monilia cinerea and 
M. FRUCTIGENA. 
(a) Apples inoculated with Strains of the Two Species. 
Experiments carried out on apples in 1916 with the object of comparing 
the action of that form of Monilia cinerea which causes the Blossom Wilt 
disease of apple trees with that of a strain of M. cinerea isolated from a plum 
affected with Brown Rot, and with that of a strain of M. fructigena also 
obtained from a plum, have already been described in a previous paper (1917). 
It was there shown that the mode of development of the Blossom Wilt 
form of Monilia under those conditions (growing on immature apples in 
the laboratory) was different from that of either of the other two forms 
in that the brown coloration of the affected areas rapidly became dark 
brown and finally black in the case of the Blossom Wilt strain, while the 
1 Loc. cit., p. 174. 2 Loc. cit., p. 33. 
3 The writer has found the method here described (slightly modified in the case of spores or 
. conidia which do not float in water) of obtaining ‘ single spore strains ’ suitable for other fungi with 
reproductive bodies large enough to be easily seen under a low power of the microscope. 
