242 Transactions British Mycological Society. 
Myxosporium corticolum in enormous numbers. The method by 
which the fungus enters the tree in this case can only be con- 
jectured, but it evidently came from the region of the ground. 
SUMMARY. 
1. Myxosporium corticolum Edgert. is the cause of bark 
canker disease. 
2. A characteristic of the disease is the formation of large 
longitudinal scars on the sides of branches, on the dead tissue 
of which numerous acervuli are found. 
3. The scars increase rapidly at one period of the year only, 
usually towards the end of the summer. 
4. The fungus is most abundant in the cortex, but also occurs 
in the phloem, and the wood. 
5. In the wood infected by the hyphae wound gum is formed 
in large quantities in the wood vessels and in the thick walled 
wood parenchyma, but not in the medullary rays, the phloem, 
or the cortex. 
6. Wound gum is formed in advance of the hyphae. 
7. Conidia are produced in acervuli; they are oval or slightly 
allantoid in shape and measure 25-45 x g-I8p. They ger- 
minate easily. 
8. In pure culture hyphae grow very slowly, preferring 
gelatine to agar. On certain media the hyphae secrete drops of 
brown liquid which contain oxalic acid. Crystals of calcium 
oxalate are invariably found in the media on which Myxosporium 
corticolum has been growing. 
g. In pure culture conidia have only been formed on apple 
twigs and 2% malt agar. In the latter case they are formed 
inside a dark green body, in appearance like a sclerotium. 
to. As a result of inoculations, Myxosporium corticolum 
seems to be a weak parasite except under certain conditions. 
When these conditions are reached, however, much permanent 
damage is done to the trees and they may be killed outright. 
11. The fungus in some cases enters through a dead spur; 
in other cases infection comes from the region of the ground. 
Infection may also take place through grafting wounds. 
I take this opportunity of thanking Mr S. P. Wiltshire who 
originally suggested this investigation, and also provided 
material, and took an active interest throughout. 
I also wish to thank Professor O. V. Darbishire and Professor 
B, T. P. Barker for their advice and interest in this work. 
CRYPTOGAMIC RESEARCH LABORATORY, 
THE UNIVERSITY, 
BRISTOL. 
November, 1922, 
