FUNGOID PESTS OF TIMBER 151 



are an essential to the completion of the life 

 histories of most of the Rusts. For example the 

 rust of Ash, Puccinia fraxini, winters on Marsh 

 grass ; the Pine-bUster, Peridermium pini, com- 

 pletes its life cycle on the Groundsel ; the Spruce 

 fir rust, Aecidium abietinum, has the Rhodo- 

 dendron as one of its hosts ; the rust of Pinus 

 strobus is parasitic also upon Currant bushes, and 

 the same fungus attacks Junipers and Hawthorn. 

 There are some fungi which attack converted 

 timber. Polyporus vaporarius, though a wound 

 parasite, will, under favourable circumstances, 

 attack stacked timber. Of all the timber dis- 

 eases by far the most injurious is " dry rot," 

 MeruUus lacrymans. The conditions most favour- 

 able to the germination of dry rot spores are bad 

 ventilation, warmth, moisture and an alkahne 

 medium on which to grow. When badly attacked 

 by this fungus the wood is riddled by the fungus 

 hyphse and its surface is coated with a grey felt 

 of mycehum. This vegetative growth may 

 spread over intervening spaces to other timber. 

 The effects of dry rot are most disastrous to 

 infected timber. The hyphee penetrate to the 

 pith rays, for there some of the cells retain their 

 protoplasm from which the fungus obtains its 

 nitrogenous food. From the walls of the wood 

 vessels carbon and mineral matter are obtained. 

 Infected wood rapidly becomes lighter in weight, 



