Larch and Spruce Canker. 



i/7 



any account of actual experiments, and is quite contrary to my 

 own experience. One hundred and four inoculations on young 

 unwounded branches of larch, in some instances seedlings, in 

 others old trees, extending over several years, made at different 

 seasons and under varied conditions, by using fresh ascospores 

 which germinated readily in water, invariably resulted in failure 

 to infect the branch experimented upon. The same failure 

 attended eleven experiments of inoculation with the conidia of 

 D. calycina. 



On the other hand, inoculation by means of placing asco- 

 spores, or mycelium contained in either wood or resin, on a 

 wounded surface, almost invariably resulted in establishing the 

 disease, the only accepted evidence being the production of 

 conidia or ascophores. 



Branches two or three years old are most susceptible, and 

 out of numerous experiments I have never succeeded in 

 inoculating a branch when more than five years old. 



Quite young trees — under ten years — are much more readily 

 inoculated than older trees, although I have sometimes 

 succeeded in inoculating young branches of very old trees. 



I have never succeeded in producing canker by using the 

 conidia (=spermatia of some authors) of the fungus for 

 inoculation purposes, even when deposited in quantity in a 

 protected wound ; nevertheless, the conidia germinate freely 

 when placed in contact with a very thin section of larch bark- 

 in a hanging drop (Fig. 6). The ascospores also germinate 

 and push out strong germ-tubes under similar conditions 

 (Fig- 7)- 



Hartig (i) who like Willkomm (3) figures the conidia as 

 elliptical, whereas I find them to be perfectly globose, did not 

 succeed in causing these bodies to germinate, and states, 

 distinctly that the conidia are incapable of infecting the larch ;. 

 this statement is repeated by Marshall Ward (4). Although, as 

 already stated, I have never succeeded in producing canker bv 

 inoculation with conidia, yet the fact that these bodies do 

 germinate, an 1 their constant presence along with the cups 

 or ascophore form of fruit on canker wounds, seem to suggest 

 that possibly they may under certain undiscovered conditions, 

 be the cause of the disease. The conidia-bearing pustules 



M 



