Wormald ’ — ‘ Brown Rot ’ Diseases of Fruit Trees . //. 1 6 1 
cherry in March bore conidia of which the average size was 11-5 x 8-o/x ; 
when isolated and grown on a young plum in the following July the average 
was 18-0x13*0 }jl. The corresponding figures for a strain found on a 
mummied plum and later grown on a young plum were 11-5 x 8-o \x (March) 
and 19*0x13-5 /x (July). 
A strain isolated from a plum twig gave the variation in the average 
size of its conidia shown in the following table : 
Conditions under which the Conidia 
were produced. 
Plum twig 
Plum inoculated from pure culture 
ditto ditto 
Culture on sterilized potato in labora- 
tory 
Mummied plum, result of inoculation in 
previous year 
Date. 
Range 
of 
Variation. 
.Average. 
Mar. 
27 , 
1917 
5-5 x 5' 
>0- 
■14.5 X 
9.0 n 
10.5x7.0 ix 
July 
18, 
1917 
io-o x 7 
■5- 
-27.0 X 
19-5 
16.5 x 12.5 
July 
3D 
1917 
io-o x 7 
•5- 
27.0 X 
l 4-5 
16-0 x ii.o 
Nov. 
19, 
1 9 l 7 
7.5x6. 
>0- 
■25.0 X 
18.5 
16.5 X 12-0 
Feb. 
28, 
1918 
6-5x5 
.0- 
-16.5 X 
n-5 
12*0 x 8*5 
The most convincing proof of this polymorphism of the conidia was 
furnished by the strain already referred to as being isolated from a Brown 
Rot canker of an apple tree in 1916 and used in inoculation experiments on 
apple flowers during three successive seasons ; the results are here tabulated : 
Conditions under which the Conidia 
were produced. 
Brown Rot canker 
Culture on sterilized potato in labora- 
tory 
Pedicel of apple flower inoculated from 
pure culture in May, 1916 
Dead spur, result of inoculation from 
pure culture in.May, 1916 
Pedicel of apple flower inoculated May 
I 9 I 7 
Dead spur, result of inoculation in 
May, 1916 
Plum inoculated from pure culture on 
June 24, 1918 
Date. 
Range of Variation. 
Average. 
Apr. 
May 
15, 1916 
5> 19 16 
7.0 X 6*0-14*0 X 10*5 [X 
9.0 x 7-0-26-0 X 20-0 
1 1.0 X 8-0 fX 
18.0 x 13.5 
July 
11, 1916 
9.0 x 7.0-21.5 x 15.0 
I5.5 X 12*0 
Feb. 
*3, i9 x 7 
6.0 x 5.0-15.0 x 10.5 
1 1.0 x 8.5 
May 30, 1917 
14.0 x 1 1.0-26-0 x 19.5 
18.0 x 14-5 
Mar. 
22, 1918 
6*o x 4.0-16.0 x 1 1.5 
11.5x8.5 
July 
4, 1918 
9.5 X 8.0-26*5 X 20-0 
19.0 x 14-0 
That the nature of the substratum on which a fungus is growing may 
determine the size of the conidia has been observed by Neger ( 19 ) in certain 
Erysiphaceae and by Brierley ( 4 ) in Botrytis cinerea . 
The seasonal variation in the dimensions of the conidia, which is so 
striking in Monilia cinerea , is much less noticeable in the case of Monilia 
fructigena , which produces conidia freely only during the warmer months of 
the year. In general the conidia of M. fructigena are larger than those of 
M. cinerea : 
Dimensions of Conidia of Monilia fructigena. 
Source of Conidia. 
Date. 
Range of Variation. 
Average. 
Mummied apple, old pustules redeveloping 
June 26 
ii-o x 9-5-26-5 x 16-0 ix 
19.0 x 12.5 ix 
Plum, recently infected 
July 17 
i2-o x 8.5-31-0 X l6-0 
21.5 x 13.0 
Apple, „ „ 
Oct. 25 
13.0 x 9-0-28-0 x 16.5 
20-5x13-5 
Plum, „ „ 
Sept. 18 
12.0 x 9.0-27.5 x 15.0 
20-0 X 12-5 
Fruiting spur of apple 
Aug. 29 
12*5 X 9.5-31.0 X 17.5 
24-5x13-5 
Sept. 10 
14.5 X I I.O-29.O X I 7.0 
23-5x14*0 
M 2 
