THE FUNGI 171 



organism rather than to endeavour to extir- 

 pate it afterwards. 



Some of these destructive fungi, instead of 

 only attacking the dead tissues the wood 

 of the trees, invade and kill the living cells. 

 This is a more serious matter, for we must 

 remember that only a very small part of a 

 trunk is really alive in the strict sense of the 

 word, that is, contains living protoplasm. 

 Any pest which attacks the living tissues, and 

 especially the cambium, often speedily kills 

 it, or at any rate renders it practically worth- 

 less. Such fungi are those which produce 

 the larch canker (Dasyscypha Willkommii) and 

 the beech canker (Nectria ditissima), the 

 latter being especially destructive to the cells 

 of the cambial region and thus producing 

 very dangerous lesions. 



One of the most interesting of the tree 

 diseases is that produced by the fungus known 

 as Armillaria mellea. The fructifications are 

 easily recognised as clusters of brown toad- 

 stool-like bodies which spring from the roots 

 or stumps of dead trees at the ground level. 

 Each " toadstool " is characterised by the 

 possession of a ring or frill underneath the 

 cap which bears the gills. Before its life 

 history became known, and consequently 

 methods could be devised to check its progress, 

 the fungus was a very dangerous one, especi- 

 ally when it invaded the pine woods, for it 

 spreads fairly rapidly from one tree to 

 another. The mycelium grows in the cambial 



