Minnesota Plant Diseases. 247 



commonly forming- squares. Wood so affected is very friable 

 and can be easily rubbed to a powder. Water passes easily 

 through such decayed parts and further aids in the invasion of 

 new portions and of other timbers in contact with it. In moist, 

 dingy cellars, where the atmosphere is always more or less 

 damp, and the timbers never have a chance to thoroughly dry 

 out, the fungus develops a vigorous, superficial mycelium, 

 which appears at first as a fine, thin, woolly coat of pure white 

 threads. This soon grows into a dense sheet of white felt 

 which can easily be peeled from the wood. In this sheet there 

 develop later thick strands composed of threads which are 

 packed with nutrient material. These strands are of great im- 

 portance as they often grow to great lengths and may carry in- 

 fection to timbers distantly located. Walls of stone or earth 

 offer no obstacles to such progress, since the fungus strands 

 are provided with a great amount of nutrient material. When 

 they finally again enter the wood they establish a mycelium 

 which supports itself upon the wood tissues. 



The fungus is also remarkable on account of its ability to 

 attack almost perfectly dry wood. It can absorb sufficient 

 moisture from the air to keep it from drying up and may thus 

 slowly destroy the wood. The excess of moisture absorbed by 

 wood attacked by this mycelium often condenses out into drops 

 on the infected parts and has given rise to the common name of 

 "weeping pore fungus." 



The fruiting bodies are flat and prostrate and never form 

 shelves. At first they are white, then reddish and later turn 

 dark yellow brown on account of the numerous spores pro- 

 duced on the surface. Wrinkles and folds form on the surface 

 of the fruiting body and shallow pores are thus produced. The 

 spores are dark yellow-brown and very small. It has been esti- 

 mated that 65,000 millions could be crowded into a space of 

 one cubic inch. The fruiting bodies are often five or six inches 

 in diameter. In one end of the spore wall is a thin place 

 through which the germ tube emerges when germination takes 

 place. This pore is closed with a small plug and it has been 

 claimed that this plug is removed only in the presence of alka- 

 line material, as wood ashes, coal dust and humus materials. 

 After the removal of the plug the germination can proceed as 



