DETAILED ACCOUNT OF SPECIFIC PLANT DISEASES 553 



endospores measure 10 to 20^ by 4 to 5/i. (2) Another kind of spore is the 

 thick-walled chlamydospore which is cylindric in shape, borne in chains 

 and measures about 12/x in width. (3) The third kind of spore is the 

 ascospore, which is borne in evanescent asci in simple perithecia. The 

 ascospores are unicellular and measure about 12/iby 5/i. 



To check or control the disease sterilization of the soil has been 

 practised. All diseased roots about the place should be destroyed by 

 fire. 



Timber 



Decay (Stereum frustulosum (Pers.), Fr.). — The fruit bodies of this 

 fungus appear as slightly raised gray spots thickly placed on the 

 surface of wood and timber (Fig. 85). The fruiting bodies are 2 

 to 5 mm. in diameter. The action of this fungus on structural wood is 

 characteristic, as it forms pocket-like areas in the decaying wood, 

 causing changes in the wood fibers. The holes are more or less len- 

 ticular and are isolated from each other by the sound wood. Layers of 

 white cellulose fiber line the margin of the hole. 



Other decay producing fungi are punk fungus, Fomes igniarius 

 (Figs. ig8, 199, 200) and hedgehog fungus, Hydnum erinaceus (Fig. 

 201). 



Dry-rot {Merulius lacrymans, Schum.). — The dry-rot fungus (Der 

 Hausschwamm) is one of the best-known and most destructive of wood- 

 destroying fungi. For many years, it was claimed, that it was purely 

 domestic found only in connection with the structural wood-work of 

 houses and buildings, but Hartig drew attention to the fact, that it 

 probably exists occasionally in a state of nature. Professor von 

 Tubeuf sums up the evidence of Hartig^ and a number of other observers 

 in this statement: "Hausschwamm ist bisher ganz auffallend selten, 

 direkt als botanische Raritat, im Walde gefunden worden. Die 

 wenigen Funde, welche bis jetzt bekannt wurden, sind nicht etwa in 

 urwaldahnlichen Forsten gemacht, sondern in der Nahe der mensch- 

 lichen Kultur; in solchen Waldern, die in der Nahe grosser Stadte 

 liegen, oder an Orten in der Nahe von Waldhausem und von Wegen, 



1 Mez, Dr. Carl: Der Hausschwamm und die ubrigen holzzerstorenden Pilze 

 der menschlichen Wohnungen, Dresden, 1908, page 260; Moller, Dr. A.: Haus- 

 schwamm forschungen im amtUchen Auftrage. Jena, Band i, 1907; Band ii, 1909; 

 Band iii, 1909. 



