GROUPS OF PLANTS. 



29 



mass is more or less cellular in structure and is known as the 

 SCLEROTIUM. It is quite resistant and usually remains dormant 

 until the following spring when the grasses are in flower again. 

 The sclerotium then shows signs of renewed activity by the de- 

 velopment of small, reddish, spherical bodies with a fair-sized 

 stalk (Fig. 19, C). Within the periphery of these spherical heads 



Fig. 20. Agaricus campestris, the common edible mushroom, showing at A on the 

 left mycelium (m) and development of buttons or young mushrooms; I to V, longi- 

 tudinal sections showing successive stages in development of fruit body; m, mycelium; 

 St, stipe; 1, portion between veil (v) and spore-bearing portion (h). 



The illustration to the right (A, B, C) shows the structure of the hymenium in different 

 degrees of magnification: A, section through portion of pileus showing five of the gills; 

 B, section 01 a gill somewhat magnified; C, section of gill still more magnified and showing 

 sterile cells or paraphyses (q) , and the fertile cells or basidia (s) , from each of which arise two 

 basidiospores. — After Sachs. 



are produced flask-shaped perithecia or ascocarps (Fig. ig, D) 

 containing numerous cylindrical asci (Fig. 19, E), each of which 

 contains eight spores (Fig. 19, F) ; the latter are one-celled, hya- 

 line and thread-like (Fig. 19, H). These spores are carried by 

 the wind to the flowers of certain of the grasses, as already stated, 

 and the life history or cycle of growth begins again. 



