SAP-ROTS OF SPECIES OF DECIDUOUS TREES. 55 



germinate where a sufficient amount of water and air is available, 

 and the rapidly growing hyphae spread through the wood, starting 

 with the medullary rays. The fungus first of all attacks the sugars 

 and starches stored in the sapwood, and then it attacks the woody 

 fiber itself. 



The character of the growth of Polystictus versicolor is well shown 

 in figure 6. In its early stages the affected wood usually becomes 

 paler in color, and following very soon after this bleaching effect the 

 wood begins to take on a disintegrated appearance, so that it becomes 

 what is known popularly as "punky." It has lost all of its usual 

 characteristics of hardness and strength and has turned into a soft, 

 dry, nonresistant, pithy mass, which is usually more or less straw 

 colored. 



The minute changes which take place in the wood fiber consist of a 

 rapid solution of various parts of the woody structure in its entirety. 

 In other words, the fungus has no special preference for either the 

 lignin or cellulose parts of the cell wall. Now and then one may find 

 a condition in the last stages of decay in which some of the w T ood 

 fibers have become delignified. When such wood is stained with 

 chloriodid of zinc the whole wall of certain groups of wood fibers 

 seems to be corroded away. In badly decayed wood the only parts 

 of the original cell which remain recognizable are those parts of the 

 original walls common to two or three cells. Among the partially 

 consumed fragments of the original wood cells one may find scattering 

 complete cells ; in fact, there is no difference in the extent and degree 

 of decay in different parts of the same annual ring. The more open 

 spring wood falls apart more readily because of its porous nature, but 

 no evidence has been obtained that it decays more rapidly than the 

 denser summer wood. The changes just referred to are practically 

 the same for all classes of woods affected. 



Like all sap-rotting fungi Polystictus versicolor is especially de- 

 pendent for its development upon the presence of a sufficient quantity 

 of w r ater and air. It will usually grow with the greatest vigor close 

 to the surface of the soil. Its fruiting bodies may therefore be 

 looked for at or near the ground line on ties, poles, posts, and all 

 timbers exposed to the soil. Where wood has time to dry out par- 

 tially on the. outside after it is cut, the spores will not usually germi- 

 nate on the outside, on account of lack of water. Infection of such 

 partially dried wood usually takes place through some season check. 



This fungus may start development in a stick of wood within a few 

 weeks after it has been cut; or, in other words, shortly after the wood 

 becomes sufficiently dry on the outside to form season checks. After 

 it has once gamed entrance below the surface, the mycelium will 

 grow vigorously in the w r ood and give absolutely no evidence of its 



149 



