THE LARCH CANKER 79 
It should here be noted that when growing saprophytically 
the fungus is generally smaller in all its parts than when 
taken from a canker spot. The saprophytic form is seldom 
more than 2 mm. in diameter, whereas the parasitic one 
may be as much as 3 mm., and the asci of the former are 
about 140-170 x 9-12 p, and of the latter 160-200 x 10-15»; 
and the spores 17-20 X 8-9, in the one case and 20-23 x 
9-10 in the other. 
The spores are here measured in each case when ripe and 
ejected and placed in water. When measured inside the 
asci they are always somewhat smaller. 
At first I was inclined to regard these as two distinct 
varieties of the fungus, but that they are only different 
growth forms is shown by the following considerations : 
1. A canker may be produced by inoculation with 
mycelium grown from the spores of the saprophytic form. 
2. Mycelium grown from the spores of the parasitic form 
will grow readily on dead larch twigs, and produce apothecia. 
3. When a young tree with canker dies the fungus spreads 
centrifugally from the canker and produces numerous 
fructifications of the saprophytic type. 
4. All intermediate forms between the two types can be 
found. 
The large apothecia of the parasitic form are probably 
the result of differences in the substratum, the most obvious 
of which is the presence of a vastly greater amount of resin 
in the canker than in the bark of a dead branch. 
