304 STUDIES OF AMERICAN FUNGI. 



forming a pavement, as it were, over the entire surface of the gills. 

 Some of them put out four little prongs, on each of which a spore is 

 borne, while others simply remain as sterile cells (Figs. 249, 250). 

 The spore-bearing cells are basidia ; the others are called paraphyses. 

 They resemble each other very much, except that the basidia bear 

 four sterigmata and a spore on each. In a few species the number of 

 sterigmata is reduced to two and in some low forms the number is 

 variable. The layer just beneath the basidia is usually more or less 

 modified, being often composed of small cells different from the rest 

 of the trama. This is called the suh-hymenial layer or sub-hymenium 

 (Fig. 250). 



Other cells called cystidia occur in the hymenia of various species 

 distributed through nearly all the genera of the agarics. Cystidia 

 are large, usually inflated, cells which project above the rest of the 

 hymenium (Fig. 250). They originate either like the basidia, from 

 the sub-hymenial cells (Fig. 250), or from special hyph^ deeper 

 down in the trama of the gill (Fig. 249). They are scattered over 

 the entire surface of the hymenium, but become more numerous on 

 the edge of the lamella. Their number is much smaller than that of 

 the basidia, but in some species where they are colored they may 

 greatly change the appearance of the gills. Cystidia often secrete 

 moisture which collects in drops at their tips, a phenomenon common 

 to all free fungous cells. 



The stem. The stem is usually fixed to the center of the pileus, 

 but it may be eccentric, i. e., fixed to one side of the center, or entirely 

 lateral. When the stem is wanting the pileus is sessile. With 

 regard to its interior the stem is solid, when it is evenly fleshy 

 throughout (Fig. 246), or hollow when the interior is occupied by a 

 cavity (Fig. 248). If the cavity is narrow and tubular the stem 

 IS fistulose (Fig. 245) ; and if the center is filled with a pithy sub- 

 stance it is stuffed (Fig. 243). These terms apply only to the nat- 

 ural condition of the stem, and not the condition brought about by 

 larvas, which eat out the interior of the stem, causing it to be hollow 

 or fistulose. 



The terms applicable to the consistency of the stem are difficult 

 to define. In general, stems may be either fleshy or cartilaginous. 

 The meaning of these terms can best be learned by careful study of 

 specimens of each, but a few general characters can be given here. 

 Fleshy, fibrous stems occur in the genera Clitocybe and Tricholoma, 

 among the white-spored forms. Their consistency is like that of the 

 pileus, namely, made up of fleshy, fibrous tissue. They are usually 

 stout, compared with the size of the plant, and when bent or broken 



