V EG ETA TIVE REP ROD UCTION. 



223 



317. Arrangement. — Simple sporangia may occur singly 

 or they may be aggregated. When a 



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 

 inner face is the hymenium. In 

 an allied form, the morels (fig. 

 227), the fructification is differ- 

 entiated into a stalk carrying an 

 enlarged head marked by narrow 

 ridges separating broad shallow pits 

 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- 



Fig. 222. — A cup fungus (Peziza 

 aurantid). A, three fructifica- 

 tions, about natural size. The 

 inner surface of the cup is covered 

 with a hymenium, a bit of which 

 is shown at B in section at right 

 angles to surface. />, paraphyses ; 

 a, an ascus bursting to allow 

 escape of spores. Highly magni- 

 fied. — After Kerner. 



The hymenium extends 



