THE DESTRUCTION OF WOOD BY FUNGI 373 



Polyporus squamosus is usually a wound parasite. Its spores 

 in all probability germinate upon the wound surfaces of broken 

 branches, where the mycelium can make its way directly into 

 the wood. There is no evidence to show that an uninjured tree 

 can become infected. The bark of trees appears to be fungus- 

 proof. It entirely resists penetration of any germ-tubes from 

 without. So far as the writer's experience has gone, fruit-bodies 

 of the fungus are always to be found actually upon or near 

 obvious wound surfaces, where the wood has been laid bare, so 

 that germ-tubes could have made an entrance directly into it. 

 As trees get older they become more and more liable to have 

 wood surfaces exposed, owing to damage by wind, snow, 

 lightning, frost, etc. The older trees become, therefore, the 

 more likely they are to be infected by wood-destroying fungi. 

 In parks and gardens, for various reasons, branches are fre- 

 quently cut from Horse Chestnut trees, Sycamores, Beeches, 

 etc., and thus admirable wound surfaces prepared by which 

 P. squamosus, or any other wood-destroying fungus, may make 

 its way into the trunk. The experience of the writer goes to 

 show that in many cases infection has almost certainly taken 

 place in this way, fruit-bodies having subsequently appeared on 

 the wound surfaces. When branches are sawn off valuable 

 ornamental trees, the exposed surfaces left ought to be at once 

 creosoted or treated with some other antiseptic, to prevent the 

 germination of spores. If this is not done there is always con- 

 siderable risk that wood-destroying fungi will enter the trees 

 and gradually cause their decay. When a mycelium has once 

 established itself in a tree-trunk, it cannot be killed or its growth 

 checked without injury to the tree itself. 



When the mycelium of Polyporus squamosus has entered a 

 large branch, guided by the wood cells, it makes its way 

 gradually to the centre of the tree-trunk, and then spreads 

 upwards and downwards in it, causing it to rot from within 

 outwards. The fungus spreads slowly to the periphery, thus 

 reducing every year the amount of sound wood. The con- 

 duction of water up the stem appears to be slowly interfered 

 with. At any rate one notices a gradual dying away of the 

 branches of an infected tree. Finally the whole tree may 

 succumb, but, if it is large, its death is often long delayed. 

 Fruit-bodies may appear annually for ten or more years upon 

 an Elm or Sycamore, whilst it is still living. The wood, how- 



