y EG ETA TIVE REP ROD UCTION. 



223 



317. Arrangement. Simple sporangia may occur singly 

 or they maybe aggregated. When 

 aggregated, they usually stand side 

 by side, and constitute a layer, 

 called the hymenium (figs. 222, 

 226). (Compare ^[ 314.) When 

 thus aggregated (and even when 

 single) they may be enclosed by 

 a jacket formed by the coalescence 

 of sterile filaments, as in the mil- 

 dews, in which the whole structure 

 constitutes a fructification (figs. 

 223, 224, 337). In the lichens the 

 hymenium, during its earlier stages, 

 is partially enveloped by sterile 

 filaments forming a cup-like apo- 

 thecium (figs. 225, 226). In the 

 cup fungi (fig. 222) the fructifica- 

 tion, which is the only part of the 

 fungus above the substratum, is a 

 single apothecium, whose whole 



. . FIG. 222. A cup fungus (Peziza 



inner race is the hymenium. In aumntta). A, three fructifica- 



tions, about natural size. The 



an allied form, the morels (fig. inner surface of the cup is covered 



with a hymenium, a bit of which 

 is shown at />' in section at right 

 angles to surface. />, paraphyses ; 

 a, an ascus bursting to allow 

 escape of spores. Highly magni- 



enlarged head marked by narrow fied. After Kemer. 

 ridges separating broad shallow pits. The hymenium extends 

 over the surface of these depressed areas. In other fungi, 

 the sporangia are sunk in deep, narrow-mouthed pits with 

 which the outer part of the fructification is filled (fig. 228). 



The simple sporangia of some of the red seaweeds show a 

 transition to the compound type in being formed by an in- 

 ternal cell of the thallus (fig. 229). The adjacent cells, how- 

 ever, do not constitute a special wall, nor are they neces- 



227), the fructification is differ- 

 entiated into a stalk carrying an 



