140 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



and the ordinary observer can j&nd no trace of the invading 

 fungus, or of disease, but if it starts in a bed of dead and dying 

 cells capable of yielding it sufficient food-materials (the hyph^e 

 can grow in a matrix flooded with turpentine) its rate of 

 spread depends almost entirely on what resistance is offered by 

 the vegetative activity of the cells around. Hartig found that 

 the germinal hyphge of N. Gucurhitula find entrance into Spruce 

 Firs through the wounds caused by certain insects (especially 

 Graioholitha ]jactolana), and also through such as are caused by 

 the heavy blows of hailstones, which bruise and tear the tissues 

 of young shoots. In the case of other Nectrias, which cause 

 wounds on non-coniferous trees, I have convinced myself that 

 ruptures caused by frost, mechanical injuries {e.g., such as are 

 produced by climbing trees to pluck fruit, &c.), pruning, &c., 

 afford the opportunities of entrance to the fungi. 



There is a deeper problem beneath all this, however, and 

 that refers to the exact nature of the mutual actions and re- 

 actions between the hyph^ and the living cells of the host ; all 

 I can say here is that it is pretty clear that the hyphae excrete 

 some poison-like substance which the living cells of the cortex 

 and cambium either break up and destroy, or merely resist the 

 action of, so long as they are strong, well-fed, and vigorous. 

 Once let such cells fall below a certain standard of health and 

 activity, however, and the hyphge make their way in and 

 demolish all before them. Obviously the factors of the in- 

 organic environments — soil, temperature, light, atmosphere, 

 and so on — may determine the balance of events in this con- 

 nection. 



In conclusion, I may add that Nectria Gucurhitula is not 

 uncommon in this country, where it is usually found on dead 

 branches, and Farlow reports the occurrence of this species on 

 Pinus Strobus in the United States, and of several other species 

 on other North American Conifer^e. 



The Douglas Fir {Pseudotsuga Douglasii) has, so far, shown 

 but few fungus diseases in this country and on the Continent, 

 but since Agaricus mdlcus and Trametes radicijjerda are among 

 its enemies, it is not improbable that it may be found to suffer 

 from maladies not found on it in (or at least not reported from) 

 its native country. Farlow adds Trametes Fini to the list of 

 its hymenomycetous enemies. 



