74 OF WOOD IN GENERAL. 



neglect, broken branches being left untrimmed as a lodgement 

 for the spores of the fungus. We have known an Elm-tree to be 

 divided in this waj^ by a broad zone of touchwood, originating 

 from the attack of a Polyporus on a snag, so that, though sound 

 timber both above and below, the tree snapt readily in half in a 

 slight gust of wind. 



Another species of Polyporus, P. vapordrius, though it acts as a 

 wound-parasite on coniferous trees, frequently develops and does 

 its chief mischief in stacked timber. It is then commonly 

 confused with the true dry rot, of which we shall speak 

 presently. Its spores (which are, as in most fungi, extremely 

 minute and produced in myriads) fall into cracks of wood, 

 whether the result of injuries to timber when standing, 

 or " shakes " developed after the tree is felled and barked. As 

 their spawn-threads develop in the timber and gradually decom- 

 pose and absorb its substance, the wood shows deep red or brown 

 streaks, warps and cracks up, and becomes thoroughly rotten, 

 and is penetrated by thick snowy-white ribbons of the felted 

 fungus. In stacked timber this rot frequently develops mainly 

 in the lower, less ventilated, layers of a stack. 



Some of the diseases that show themselves conspicuously in the 

 cortex and are known as cankers may be set up by frost, by sun, 

 or by insect attack ; but in Oak, Beech, Maple, Hornbeam, Alder, 

 Lime, and Larch, canker is the result of wound-parasite fungi. 

 The spores of most, if not all, of these fungi are incapable of 

 penetrating sound cortex ; but how many are the chances that 

 bring about small ruptures of this layer ! In the case of that 

 most destructive of cankers, the Larch disease, it has been shown 

 that the fungus which produces it, Peziza Willkomnm, is far less 

 common and less deadly in the drier colder air of Alpine heights 

 where the Larch is indigenous ; but that late frosts attacking the 

 more advanced and sappy trees in the moist air of the lowlands 

 kill many a shoot and form wounds by which the spores can enter. 

 The moister and warmer air at the same time is more favour- 

 able to the growth of the fungus. Its spawn-threads ramify in 

 all directions through the wood, turning it brown and drying it 



