172 



MORPHOLOGY 



which becomes hard at maturity, forming a small nutlike body called 

 the sporocarp (fig. 396). In Salviniaceae, therefore, the sporocarp is a 

 sorus invested by an indusium. Microsporangia and megasporangia 



400 399 



Figs. 399, 400. — Azolla: 399, young sporocarp, showing a young megasporangium 

 and the developing indusium; the megasporangium has advanced to the cutting off of 

 tapetal cells (/); 400, megasporocarp, showing the terminal megasporangium with one 

 megaspore (m) surviving the degeneration of he others, and the microsporangia (»tc) 

 checked. — ■ After Miss Pfeiffer. 



begin to develop in each sorus, but only one kind matures, so that at 

 maturity there are two kinds of sporocarps (megasporocarps and 

 microsporocarps, fig. 398), both kinds occurring on the same plant 

 and even on the same leaf segment. All the sporangia have long 



