88 



MORPHOLOGY 



Hydnaceae. These are the tooth fungi, so named because the hy- 

 tnenium covers toothlike or spinelike processes. In simpler forms 

 *he sporophore resembles an incrustation, in which case the teeth are 

 on the upper surface. In other cases the teeth occur on the under sur- 

 face of a bracket-like sporophore ; while in Hydnum they are upon the 

 under surface of the pileus of a mushroom-like sporophore. 



Polyporaceae. These are the pore fungi, so named because the 

 hymenium lines tubes that terminate on the surface with porelike 

 openings. The sporophores may be incrustations, with pores on the 

 upper surface ; or bracket forms (as Polyporus), with pores on the under 

 surface; or mushroom-like forms (Boletus), with pores on the under 

 surface of the pileus. The incrusting forms and the hard, gray, 

 hoof-shaped bracket. forms are very common on tree trunks, fallen logs, 

 stumps, etc. Many are destructive to trees, the mycelium spreading 

 extensively under the bark and through the wood. 



Agaricaceae. These are the gill fungi, being the common mush- 

 rooms and toadstools, and the largest family of fleshy fungi. There are 



bracket forms, but the prevailing type 

 of sporophore is the mushroom, with 

 stipe and pileus (figs. 198, 199); and 

 in every case the hymenium covers 

 bladelike plates, which are the gills 

 (figs. 200, 201). Many of the Agari- 

 caceae also are destructive parasites 

 on trees, the mycelium penetrating 

 the host extensively. 

 The development of the character- 



Pics. 198, 199. Coprinus: 198, 

 habit, showing stipe and pileus, and 



young sporophores; 199, longitudinal istic Sporophore is as follows. The 



section, showing relation of stipe and srna ll buttons consist of interwoven hy- 

 pileus> phae. Soon the rudiments of stalk 



and pileus appear inclosed in a loosely woven envelope (volva). The 

 elongation of the stipe ruptures the volva, whose torn remnant may 

 form a ring or sheath about the base of the stipe. In many cases a 

 membrane (velum) of hyphal tissue extends in the young sporophore 

 front the margin of the pileus to the stipe, covering the gills. When 

 the velum is ruptured by the growth of the pileus, it may remain as a 

 ring of tissue (annulus) about the stipe (fig 197). 



The presence of two nuclei in the young basidium, the nuclear fusion, the two 

 successive divisions, the migration of the four nuclei into the four sterigmata and 



