BASIDIOMYCETES. 



167 



body, and radiate from the central stalk. Those which are first 

 formed extend from the edge of the pileus to the stalk; those 

 formed later reach only a longer or shorter portion of this distance, 

 according to their age. In structure the lamellae (Fig. 174) con- 

 sist of a central mass of hyphae, the trama, continuous with the 

 hyphge of the pileus ; these terminate in a layer of shorter cells, 

 the sulky menial layer, immediately beneath the hymenium which 

 is composed of basidia and paraphyses. In a few species, but not 

 in the majority, the lamellae are branched, and in some they are 

 dec uiTent. A few have the stalk placed excentrically, or it may 

 be entirely absent. 



FIG. 172. Development of Psalliota campestris : a, b, c, d show the various stages of 

 the development of the fruit- bodies and. the mycelium (m) (nat. size); e the fruit-body 

 in a somewhat later stage, slightly magnified ; / longitudinal section of e ; n first forma- 

 tion of the hymenium ; g longitudinal section of a more advanced fruit-bsdy (nat. size) ; 

 n the hymenium ; o velum partiale (see Fig. 133.) 



In the early stages of its development the fruit-body is more or 

 less enclosed in a hyphal tissue the " veil " (velum unicersale, or 

 volva). The veil at first completely encloses the young fruit-body, 

 but is afterwards ruptured as the latter grows, part remaining 

 at the base of the stalk as the " sheath " (annulus inferus)', and 

 part on the pileus as scales or warts. In the " Fly Mushroom " 

 (Amanita muscaria) the remains of the veil are especially con- 



