THE GENUS FOMES 



57 



as numerous as possible, for this entails a corresponding increase 

 of hymenial surface. The diameter of the tubes, however, must 

 always be sufficiently wide to permit of the liberation of the spores. 

 Since these are shot outwards horizontally into the tubes for a 

 distance of about 0-1 mm.,^ the tubes can never be less than this 

 in diameter. In species of Polystictus and Fomes, where the width 

 of the tubes is about 0-2-0"25 mm., the ultimate reduction con- 

 sistent with safety seems to have been attained. 



The genus Fomes, from the point of view of efficiency in the 

 production and liberation of spores, may be looked upon as having 

 fruit-bodies of a highly specialised kind. In the first place the fruit- 

 bodies are perennial. This is economical, for the old flesh is used 



Fig. 11. — Fomes cvpiiilanatus {~F. vcgttus). Vertical section through a fruit-body 

 three years old. A new layer of hymenial tubes was produced each year. 

 Reduced to i natural size. 



each year to support new hymenial tubes, and does not function 

 only once, as in the case of such annual fruit-bodies as Polyporus 

 squamosus, or those of the Agaricinese, the Hydneas, the Clavariese, 

 or the Tremellinea3. Again, most of the Fomes fruit-bodies are very 

 hard and " woody," possess no stipes, and are attached by a broad 

 surface to the wood on which they are produced (Fig. 11). This 

 gives them extreme rigidity, so that even in the course of years 

 accidents are little likely to injure them. The extreme rigidity also 



^ Vide infra, Chap. XI. 



