26 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



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 ascospores, 

 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 asco- 

 phores. 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 ( = 8permatia of some authors) of the fungus for 

 inoculation purposes, even when deposited in quantity in a pro- 

 tected 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 (1), 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 state- 

 ment is repeated by Marshall Ward (4). Although, as already 

 stated, I have never succeeded in producing canker by inocula- 

 tion with conidia, yet the fact that these bodies do germinate, 

 and 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 are very minute 

 and of a dull yellow colour, and although by no means rare, are 

 apt to be overlooked unless specially searched for (Figs. 2, 3, 

 PJ. I.). 



Wounds for artificial infection were usually made by inserting 

 the point of a lancet quite through the bark to the cambium 

 zone, exercising at the same time a little lateral pressure, so that 

 a small crack about two lines long was made. Into this wound 

 either ascospores or mycelium were introduced. When the 

 weather was very warm and dry, the inoculated wounds were 

 protected for a week by a covering of oiled paper to prevent too 



