328 BOTANY. 



carps. These are composed of parallel vertical hyphae, 

 which grow upward, and finally bend out laterally, or send 

 out lateral branches at the top, forming the umbrella-shaped 

 pileus common in many of the genera (Fig. 225, V., h). 



425. In the common Mushroom (Agaricus campestris) 

 the young sporocarp is at first composed of a mass of similar 

 hyphae (Fig. 225, /.) ; somewhat later, however, an annular 

 opening a little below the apex is visible in a longitudinal 

 section (Fig. 225, //., I) ; this enlarges, and the overlying 

 tissue becomes the pileus (Fig. 225, ///., IV., and V., h), 

 while that between the opening and the margin of the sporo- 

 carp becomes the "veil" (Fig. 225, IV. and V., v), which 

 finally, by the rapid expansion of the pileus, becomes rup- 

 tured, leaving an annular fragment (the ring, or annulus) sur- 

 rounding the stalk of the fully developed sporocarp. Upon 

 the under surface of the pileus the hyphae form a great 

 number of thin radiating plates or lamellae^the so-called 

 gills, and upon their surfaces there develops an extended 

 hymenial layer. The hymenium consists of elongated cells, 

 which are slightly club-shaped, and placed closely side by 

 side perpendicular to the gill surfaces (Fig 226, B and C). 

 Some of these cells, the basidia, are somewhat longer than 

 the rest, and have, in this species, two, and in most others, 

 four, slender projections, upon which spores (basidiospores) 

 are eventually produced (Fig. 226, C, s', s", s'"). Here and 

 there upon the hymenium there may be found larger bladder- 

 shaped cells, looking like overgrown sterile basidia ; their 

 significance is not known, and they have received the name 

 of Cystidia (Fig. 226). In some other genera the hyme- 

 nium, instead of extending over lamellae, is found lining the 

 walls of vertical pores, as in Polyjwrus, or covering depen- 

 dent spines, as in Hydnum, or spread out on the smooth 

 surface of the sporocarp, as in Stereum. 



426. The development of the spores of the Hymeno- 

 mycetes takes place, according to De Bary,*as follows : The 

 young basidia, which have much the shape of the young asci 



* " Morphologic und Physiologic der Pilze, Flechten, und Myxomy- 

 ceten," 1865, p. Ill, et seq. 



