54 



DISEASES OF DECIDUOUS FOREST TREES. 



surface of the timber upon which they happen to be growing. They 

 form readily in a moist atmosphere. They first appear as tiny masses 

 of mycelium, which grow out usually from the medullary rays, and 

 generally several within a small area. These small masses rapidly 

 grow larger, until in the course of a few days they have united in a 

 single mass visible to the naked eye. After they reach the size of 

 one-eighth inch in diameter, or thereabouts, the hy menial layer begins 

 forming on the lower surface of the knob. . A mature fruiting body 

 may be formed in about a week where the fungus is in a condition for 

 rapid development. 



The young sporophores seem at first to grow perpendicularly from 

 the surface from which they protrude, irrespective of whether this be 



a horizontal or a 

 vertical surface. 

 Very soon after 

 their appearance, 

 however, the 

 shelves assume a 

 horizontal posi- 

 tion. Where wood 

 is placed in con- 

 tact with the 

 ground, the sporo- 

 phores are fre- 

 quently cramped 

 and crowded by 

 soil or stones, and 

 in such cases the 

 growing myce- 

 lium adapts itself 

 to the available 

 space and pro- 

 duces sporo- 



Fig. 6.— An oak railroad tie with fruiting bodies of Polystictus versicolor. n 'U r . rpc;; n f 



conceivable shape and size. It is not at all uncommon to find large 

 masses of the sporophores forming in the upper surfaces of cinder 

 ballast on railroad tracks. The mycelium in this case binds the 

 individual cinders together, forming great clumps 6 or 8 inches in 

 diameter. Where two or more sporophores start on a surface in close 

 proximity they will as a rule fuse before reaching maturity, and as a 

 result of this fusion long sheets may form composed of two or many 

 sporophores which have grown together laterally (fig. 6). 



Polystictus versicolor usually starts its development in some season 

 check, although it may start to develop on the surface of a stick of 

 wood provided the same is kept in moist surroundings. The spores 



149 



