222 DISEASES OF TREES 



The spores of M. lacrymans can germinate only when this 

 plug has been dissolved or has disappeared in some way, and 

 this seems to occur only under the action of some alkali. I 

 succeeded with germination experiments only when I had added 

 some ammonia or salts of potash or soda to the infusion in 

 which the spores were placed. These salts are not to be 

 regarded as nutritive in their effects, but merely as rendering 

 possible the removal of the spore-pellicle that covers the germ- 

 aperture. Every seed and every spore contains a certain quan- 

 tity of nourishment which has been derived from the parent 

 plant, and which is instantly available for use. Only when this 

 has been used up during germination is further development 

 dependent upon a supply of nourishment from the environment. 

 I will not contest the possibility that now and then a spore 

 of M. lacrymans may germinate directly on wood, which 

 of course contains minute traces of alkalis, still I have only 

 succeeded in inducing spores to germinate on wood by adding a 

 little alkali. This explains why injuries from M. lacrymans are 

 specially apt to occur in places where urine, humus, wood ashes, 

 coal-dust, and such like are present. 



Wood is the natural food of M. lacrymans, and in this respect 

 there is no difference between summer-felled and winter-felled 

 timber. The causes of the frequent complaints regarding 

 summer-felled wood have already been discussed. 



Soil that is very rich in humus also offers nourishment to M. 

 lacrymans, though only in small quantity. It is probable, 

 although not certain, that when the mycelium is growing in 

 contact with walls it dissolves and consumes minute quantities 

 of lime, but in any case these are so small that no direct 

 damage can be ascribed to this cause. 



When alive or still fresh, M. lacrymans has a very pleasant 

 odour and delicate flavour, though this is succeeded by a some- 

 what astringent taste. When sporophores, especially large ones, 

 decompose, they disseminate a highly repugnant and very 

 characteristic smell. There is no doubt that the gases generated 

 by the decaying fungus are highly injurious to the health of 

 human beings inhabiting rooms exposed to them. In addition 

 to this, large quantities of water are evaporated from the fungus, 

 and thus rooms are kept damp. 



