446 INSECTS AFFECTING VEGETATION 



and invade the wood to a very great extent, even by adaptation to 

 parasitic habit extending their work into the living parts causing 

 death. The removal of a large branch of a shade tree or a fruit tree, 

 unless the wound thus formed is properly protected by dressingj 

 opens the way for spores of these fungi which cause timber decay to 

 obtain a start and thus eventually to invade the heartwood of the in- 

 terior. For dressing cut-off branches, asphaltum is admirable ; in its 

 lack gas tar is good, and either is better than ordinary paints. 



There is always to be borne in mind that the protection of the 

 woody cylinder of trees depends on its being covered by the living 

 layer of sap wood. Every branch of considerable size connects di- 

 rectly with the extensive heart cylinder ; we thus see that the wound 

 fungi which attack the heart wood are the timber decays and their 

 presence emphasizes the need for care in providing protection for 

 all wounds, especially those caused by pruning. 



Any decay becoming established in the dead heartwood may 

 extend for long distances through this dead wood and in the end so 

 destroy it as to be in a position to invade the external or sapwood 

 layer. 



In addition to the exposure of the internal woody cylinder to 

 these decays, we have sap-rots due to various species of fungi which 

 belong on the border line between the parasitic and saprophytic 

 sorts : Among them are species of Fomes, Polyporus, Lenzites, etc. 

 Any wound of the sapwood even though it does not reach to the 

 dark heartwood, exposes to the danger of this infection, and with 

 infection, to all the consequences of sapwood decay and premature 

 death of the tree. These decays and those of heartwood are in line 

 with those of the rots of structural timbers, but we are at this time 

 interested only in their effects on the parts of the living plants. 



TIMBER ROTS AND TIMBER PRESERVATION. 



The decay of dead logs, wooden frameworks, or other structural 

 timbers is caused by the attacks of saprophytic fungi belonging to 

 the gill and pore fungi mentioned under wounds; these are of the 

 great class of basidium bearing fungi, to which the fleshy forms, 

 everywhere more or less abundant, belong. The most of them are in- 

 cluded in the mushrooms, which there is a strong impulse now to 

 study and illustrate by photographs. These timbers are dead and are 

 subjected to invasion by 'timber infecting species wherever the condi- 

 tions as to air and moisture are such as to favor their development. 

 Dry timbers are not subject to such attack because lacking the requis- 

 ite moisture for the organism. Floors and other timbers of houses ad- 

 jacent to the earth or to unheated cellars are often attacked by rot- 

 causing species. The timbers of trestles, railway ties and the bases 

 of fence, telephone and telegraph posts, where inserted into the earth 

 or in contact with it, are kept sufficiently moist to invite attacks of 

 this sort. 



Wood that has been invaded by such fungi is reduced to the 

 state called punk : that is, the wood fibers and arrangements in vessels 

 to which the timber owes its strength, are broken down by the inva,- 

 sion of the fungus which flourishes at the expense of this woody 



