CBYPTOGAMS 



191 



bowl-shaped, or even club-shaped. The largest have 

 apothecia several inches across, but the commoner kinds 



y j3 



311. Peziza on wood. 



312. Section of apothecium; 

 /i, hymeuium. 



are a quarter inch or less in diameter. The interior of 

 the saucer is lined by a layer (liymenium, Fig. 312) made 

 up of spore sacs (Fig. 313) and sterile filaments that 

 grow up between them. When ripe, 

 the (eight) spores escape by the rupture 

 of the sac (^asciis). On germinating, the 

 spores give rise to mycelia, the apothe- 

 cia not ap- 

 pearing for a 

 considerable 

 time. 



455. Micro- 

 sphaera Alni, 

 one of the 

 Powdery Mil- 

 dews, is par- 

 asitic, often 

 on the leaves 

 of Lilac (Fig. 

 311). The 

 mycelium 

 spreads over the surface of the 

 leaf and sends haustoria (suck- 

 ing hyphse) into the interior. 

 In the earlier part of the season 



simple erect filaments arise, at 314. Lilac leaf, infected by Micro- 



the ends of which spores are spiaera. 



formed (somewhat as in Penicillium). Later, fructifica- 



A part of the liy- 

 menium, great- 

 ly magnified : a, 

 an ascus ; /, a 

 sterile filament. 



