CRYPTOGAMS 



371 



the under side of the fructifications in successive annual layers. P. igniarius (Fig. 

 296), which is often found on Willows, and has a similar structure, has «■ rusty- 

 brown colour, and furnishes, as it is much harder, a poorer quality of tinder. 



Fig. 295. — Boletus Sataims. (After Krombholz, £nat. size. Poisoxoos.) 



Many parasitic Polyporeae are highly injurious" to the trees attacked by them ; 

 thus Heterobasidion annosum often causes the death of whole forests of Pines and 

 Spruce Firs. Merulius lacrymans is an exceedingly dangerous saprophytic species, 

 attacking and destroying the timber of damp houses. The mycelium of this Fungus 

 forms large, white, felted masses, giving rise to outspread, irregularly-shaped, pitted 

 fructifications of an ochre or rusty-brown colour, and covered with a hymenial layer. 

 As remedial measures, good ventilation should be secured, and the wood soaked with 

 carbolic acid or petroleum. 



6. The Agaricineae, which include the greatest number of species, have stalked 

 fructifications, commonly known as Mushrooms and Toadstools. The under side of 

 the pileus bears a number of 

 radially disposed lamellEe or 

 gills which are covered with 

 the basidia-producing bymen- 

 ium. In the early stages of 

 their formation the fructifica- 

 tions consist of nearly spherical 

 masses of interwoven hyphse, 

 in which the stalk and pileus 

 soon become differentiated. 

 The rudiments of the stalk 

 and pileus are at first enclosed 

 in a loosely woven envelope, 

 the volva. In the course of 

 the further development and elongation of the stalk the volva is ruptured, and its 

 torn remnants form a ring or sheath at the base of the stalk, but in many cases 

 its development remains rudimentary. The fructifications are accordingly hemi- 



Fig. 296. — Polyporus igniarius. Section through an old fruc- 

 tification, showing annual zones of growth ; a, point of 

 attachment. (£ nat. size.) 



