THE LARCH CANKER 79 



It should here be noted that when growing saprophytieally 

 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 /*, and of the latter 160-200 X 10-15 ju ; 

 and the spores 1 7-20 X 8-9 /x in the one case and 20-23 X 

 9-10|u 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. 



