FUNUI INJURIOUS TO FIRS. 65 



These ywfi'iax, though very common indeed, are usually found as 

 deridedly sapi-ophytie fungi, living in the dead wood and cortex of 

 fallen branches, or the parts of trees killed by entirely different agencies 



e.g., frost, breakage, insect injuries, etc.- and experiments show that 

 the germinal tubes developed from the spores are unable to penetrate 

 the sound tissues of living branches. On the other hand, it is quite 

 easy to infect a tree if the sound cortex be punctured with the 

 point of a scalpel on which a few spores* have been rubbed. The 

 puncture kills a number of cells, and the hyphse feed on the solution 

 of food-materials thus formed; and it is only from a position of 

 advantage like this that the mycelium, waxing in vigour day by day, 

 is able to invade the tissues around, and gradually kill and destroy 

 those that are not active enough to resist it. As already said, the 

 mycelium may fail to do more than establish itself in the more worn- 

 out portions of the inner cortex, and may then be cut out and cast 

 off by layers of cork. There is considerable reason for believing that 

 it makes all the difference to the fungus what kind of start it gets; 

 if the mycelium is still young and feeble, the active tissues of the 

 cortex may cut it out very soon, and the ordinary observer can find 

 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 hyphsB 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 

 hyphse of N. Cucurbitula find entrance into Spruce Firs through the 

 wounds caused by certain insects (especially Grapholitlia pad-olana), 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 Nedrias, 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, etc.), priming, 

 etc., 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 reactions between the 

 hyphse and the living cells of the host; all I can say here is that it 

 is pretty clear that the hyphse 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 loiig as they are strong, well-fed, and 

 vigorous. Once let such cells fall below a certain standard of health 

 and activity, however, and the hyphse make their way in and demolish 

 all before them. Obviously the factors of the inorganic environments 

 soil, temperature, light, atmosphere, and so on may determine the balance 

 of events in this connection. 



In conclusion, I may add that Nedria Cucurlihila 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, 



The Douglas Fir has, so far, shown but few fungus diseases in this 

 country and on the Continent, but since Ayarirus melleus and Trametes 

 radiciperda 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 Pini to 

 F 



