1 62 Wormald. — ‘ Brown Rot ’ Diseases of Fruit Trees. II. 
That the conidia of Monilia fructigena are appreciably larger than 
those of M. cinerea when produced under the same conditions was deter- 
mined by measuring the conidia of the two species (i) when both were found 
growing on different plums of the same cluster, and (2) when both were 
growing on the same plum which had been inoculated on opposite sides 
with the two species. 
*• l 
Dimensions of Conidia of M. fructigena and M. cinerea . 
(1) O11 different plums of the same cluster. 
Species. Date. Range of Variation. Average. 
M. fructigena Sept. 18 12-0 x 9*0-2 7.5 x 15*0 /* 20.0 x 12*5 p 
M. cinerea Sept. 17 8*5x6.5-22.5x18.0 17*0x10.5 
(2) On opposite sides of the same plum, inoculated July 17. 
Species. Date. Range of Variation. Average. 
M. fructigena July 31 14*0 x 1 1*0-34*0 x 15*0 n 21*0 x 13-5 \x 
M. cinerea „ 10*0x7.5-27*0x14.5 16.0x11-0 
It follows from these results that measurements of the conidia of 
M. fructigena and M. cinerea aid in diagnosing the species, but when the 
two are grown under the same conditions it is found that the difference is not 
so great as is generally supposed. The dimensions of the conidia as deter- 
mined by continental workers are as follows : 
A uthor. 
M. fructigena. 
M. cinerea. 
Saccardo 
Lindau 
Woronin 
Schroter 
Aderhold and Ruhland 
25 X IO-I 2 [k 
20-24 x I2-I 4 
Average 20.9x12.1 
18-24 x 10-12 
18-23 x 9 -I 3 
15-17 X IO-I2 /x 
12-13 x 9 -I ° 
Average 12.IX 8-8 
15-18 x 10-12 
9.3-14.5 x 6.2-12.4 
Woronin ( 27 ) found that when M. cinerea was growing on twigs or on 
the surface of various stone-fruits the average size of the conidia was 12*1 x 
8*8 ju, ; the largest conidia he found under natural conditions measured 
13*2 x 9*9 ju. It would seem from these figures that the dimensions quoted 
were those of conidia examined early in the year, and that the larger conidia 
produced on growing fruit in summer were not observed by Woronin ; he 
found, however, that when M. cinerea was cultivated on artificially prepared 
media the average size of the conidia produced rose to 17*5x11*2 f-t. 
Lindau and Aderhold and Ruhland also probably made their observations 
on conidia produced in winter, while Saccardo and Schroter must have 
examined summer conidia. This would explain the apparent discrepancies 
in the results obtained by the various workers. 
In general terms the two species are to be distinguished by means of the 
conidia as follows : 
M. cinerea produces in winter and early spring, on cankers, twigs, and 
mummied fruit, conidia the average length of which is about 11*5 /x, 
