266 



STRUCTURAL BOTANY 



the lower surface of the pileus, as shown in Fig. 104, E 



and F. 



The tissue of the pileus is like that of the stalk, but 



rather denser. The 

 gills on the under-sur- 

 face are formed by an 

 extension of the hyphse 

 of the pileus. If we 

 cut a tangential section 

 of the pileus, we see 

 the gills or lamellae in 

 transverse section, and 

 can make out their 

 structure (see Fig. 105). 

 The middle part of each 

 lamella is formed of 

 hyphaB coming down 

 from the pileus, and 

 following on the whole 

 a longitudinal course, 

 their lateral branches, 

 however, diverging to- 

 wards the two surfaces. 

 This central tissue of 

 the lamella is called 

 the trama (Fig. 105, 

 B, C, t). Towards the 

 free surfaces the cells 

 of the diverging hyphse 

 are shorter and more 

 closely packed, forming 

 the sub-hymenial layer 

 (sh), and beyond this 



FIG. 105. Gills of Mushroom. A, part 

 of tangential section of pileus (h], 

 showing gills (I). Slightly magnified. 

 B, single gill in section ; t, trama ; sh, 

 sub-hymenial layer ; hy f hymenium ; 

 r, lower edge of gill. Magnified about 

 80. 0, part of B enlarged ; t, cells of 

 trama ; sh, sub-hymenial layer ; q, 

 paraphyses ; s^-s^, stages in develop- 

 ment of basidia ; sp, basidiospores. 

 Magnified 370. (After Sachs.) 



