144 Worm aid . — ‘ Brown Rot * Diseases of Frtiil Trees . //. 
produce a blossom wilt and cause cankers on the branches by infection 
through the flowers ; the other kills only the flower actually inoculated, 
infection extending no farther than the pedicel of the infected apple flower. 
In the following pages experiments are described which show that the 
two biologic forms of Monilia cinerea can be distinguished in the laboratory 
by biochemical methods. The value of the application of cultural methods 
to taxonomy, as illustrated by certain distinguishing characters exhibited 
by M. fructigena , M. cinerea , and an American form of Monilia when 
grown in pure cultures, is also discussed. 
II. The Secretion of an Oxidizing Enzyme by 
Monilia cinerea . 
When growing on agar, prepared with an extract of prunes as its 
nutrient constituent, at room temperature (about i8°C.), the apple Blossom 
Wilt strains of Monilia cinerea invariably give rise to a dark brown colora- 
tion. Strains from other sources developed this browning in varying degrees ; 
a few remained quite hyaline on that medium or produced merely a slight 
coloration in some cultures, while with others the colour was quite as intense 
as that of the apple strains. The fact that chromogenesis in fungi is often 
due to the action of oxidizing agents elaborated by the organisms suggested 
the presence of an enzyme (probably an oxidase) in the Monilia cultures, 
and experiments were initiated with the object of ascertaining whether such 
an enzyme could be detected and identified. The results, though they 
showed no close correlation with the coloration of the agar cultures, proved 
to be of particular interest in relation to the inoculation experiments on 
apple flowers described in Part I. 
(a) The Enzyme in Liquid Culture Media . 
Preliminary experiments were carried out with two strains used in the 
inoculations of apple flowers made in 1917, viz. an apple Blossom Wilt 
strain, and one obtained from a vegetative shoot of a plum tree affected 
with the ‘ Wither Tip ’ disease. The former, in common with all other 
strains obtained from apple spurs and cankers, developed a dark brown 
coloration on prune extract agar, while the latter in a few cultures produced 
a little browning, but generally remained quite hyaline. The Wither Tip 
strain had failed to produce a blossom wilt when apple flowers were inocu- 
lated with it. 
In the first experiment of this series the two strains, here referred to 
for convenience as A (apple strain) and B (plum strain) respectively, were 
grown at room temperature in Petri dishes containing a sterilized extract of 
apples. After 16 days the liquids were poured from the dishes into wide 
test-tubes, when it was seen that in both cases they were darker than the 
