134 



FIRST GROUP.^-THALLOPHYTES. 



the pileus is spread out horizontally by the stretching of the tissue, the membrane (the 

 velum partiale) parts from its margin and hangs down like a frill on the stalk. 



It was said above that the hymenium covers the surface of the lamelliform, conical, 

 or tubular projections on the under side of the pileus. A tangential section of the latter 

 gives in all three cases much the same result as is seen in Fig. 90, which is taken from 

 Agariciis campestris. ^ is a piece of a tangential section of the disk of the pileus, h the 

 substance of the pileus, / the lamellae. ^ is a portion of one of the lamellae more 

 highly magnified to show the course of the hyphae ; the body of the lamella /, called 

 the trama, consists of rows of elongated cells which spread right and left from the 

 median plane of the trama to its margins, where the hyphal cells are short and round, 



Fig. 89. A^aricits campestris, nat. size. See the text. Fig. 90. Agaricus cafnfiestrts > formation of the hymenium. A 



and B slightly magnified, C a part of B magn. 550 times. The portion 

 marked with fine dots is protoplasm. 



and form the subhymenial layer [sh B and C) ; from these short cells spring 

 club-shaped tubes q, placed close to one another and perpendicularly to the surface of 

 the lamella, which together constitute the hymenial layer [B, hy). Many of these tubes 

 are sterile and are named parapJtyses, others produce the spores and are the basidia. 

 Each basidium in this species produces only two spores, in other Hymenomycetes 

 usually four. The basidium sends out first of all as many slender branches, sterigDinia 

 s', as there are spores to be formed ; each of these branches swells out at its extremity, 

 the swelling enlarges and becomes the spore (s", s"), which drops from the stalk on 

 which it was formed, and leaves it behind (/'"). 



