W or maid. — ‘ Brown Rot ’ Diseases of Fruit Trees. II. 167 
The biological relationship of the two species to their host is also 
different. Observations made in Kent on affected trees, and on specimens 
received from other counties, show that the species occur on apples, plums, 
and cherries as shown in the following table. Observations on other hosts 
have not been sufficiently numerous for a general statement to be made of 
their mode of attack. 
Host. 
M. fructigena. 
M. cinerea. 
Apple trees. 
Produces a fruit rot and may cause 
cankers by invading the branches 
Produces a blossom wilt and often causes 
cankers by invading the branches 
from the fruit. 
through the flowers and flowering 
Plum trees. 
Causes a fruit rot. 
spurs. 
Produces blossom wilt, cankers, and 
fruit rot. 
Cherry trees. 
Causes a fruit rot. 
Produces blossom wilt and may kill 
twigs ; it also causes a fruit rot. 
Not only are there two distinct species of Monilia concerned in the 
Brown Rot diseases, but there is evidence, as presented in the preceding 
pages, that in Britain there are two biologic forms of M. cinerea , which may 
conveniently be referred to as forma mali and forma pruni ; these may be 
distinguished as follows : 
Monilia cinerea forma mali. 
Produces a blossom wilt and canker of apple 
trees. 
Readily secretes an enzyme which oxidizes 
tannins. 
M. cinerea forma mali appears to be confined to the apple ; I have not 
yet found it on plums or cherries, although artificial inoculations have 
shown that it is able to infect the flowers and fruit of the plum tree. 
M. cinerea forma pruni is the form occurring on plums, cherries, and 
damsons ; it is found also on Pyrus japonica. The fact that it is unable to 
invade the flowering axis of the apple tree to cause a blossom wilt accounts 
for its inability to establish itself on that host. 
A comparison of the morphological and cultural characters of strains of 
M. fructigena and M. cinerea isolated from mummied fruit sent by 
Dr. Quanjer from Holland showed that the two species occurring in this 
country are similar to those of the Continent. I have not yet been able 
to secure specimens of M. cinerea f. mali from abroad, but the description 
and illustrations given by Eriksson (8) of a disease of apple trees occurring in 
Sweden conform so closely with the appearance of the ‘ Blossom Wilt and 
Canker ’ disease of apple trees occurring in this country that there is good 
reason for assuming its occurrence on the Continent. 
There is no record of the occurrence in Britain of the ascigerous stage 
in the life-history of either Monilia cinerea or M. fructigena , and all attempts 
at Wye to induce the development of apothecia by placing mummied fruit 
on the ground in the open have hitherto failed. 
Monilia cinerea forma pruni. 
Unable to cause a blossom wilt of apple trees. 
Secretes the oxidizing enzyme far less freely. 
