FUNGI. 207 



tures, can only be conceived by those who have 

 witnessed them. " I knew a house," writes Mr. 

 Burnett, "into which the rot obtained admittance, 

 and which, during the four years we rented it, had 

 the parlours twice wainscoted and a new flight of 

 stairs, the dry-rot having rendered it unsafe to go 

 from the ground floor to the bedrooms. Every pre- 

 caution was taken to remove the decaying timbers 

 when the new work was done, yet the dry-rot so 

 rapidly gained strength that the house was ultimately 

 pulled down. Some of my books which suffered least, 

 and which I still retain, bear mournful impressions 

 of its ruthless hand ; others were so much affected 

 that the leaves resembled tinder, and when the 

 volumes were opened fell out in dust or fragments." 

 The decay of the wood is partly due to the growth 

 of the fungus, especially the mycelium, which decom- 

 poses the tissues, and partly to the moisture which 

 this loosening effects and is the means of introducing 

 into its interior. The germs fall into the chinks of 

 the wood, and germinate, widening the chinks by 

 their growth, and thus permit more moisture to 

 permeate, so that by a continuous repetition of 

 these processes the whole strength of the timber is 

 destroyed. It cannot be too often urged that mois- 

 ture and exclusion of air are the primary factors in 

 the spread of rot. If by any means all moisture can 

 be got rid of, by establishing a thorough current of 

 dry air, the fungus of the dry-rot is sure to succumb. 

 As soon as a condition of dryness is established the 

 filaments will shrivel and decay. The spores can 

 only germinate in a sufficiently moist atmosphere, 



