174 



MORPHOLOGY 



membrane, from the surface of which there arise remarkable appendages 

 (glochidia) that resemble hairs with sagittate tips (fig. 403). About the 

 single megaspore the matrix forms a heavy and often elaborate pennium 

 (p. 147 ) or epispore (fig. 406). 



Male gametophyte. • — The microspore germinates within the sporan- 

 gium of Salvinia, and within the discharged massulae of Azolla, in both 

 cases sending out a tube to the surface, the external part of which is cut 

 off by a wall (fig. 404). This external, water-exposed cell is the anthe- 

 med* 



Fig. 402. — Azolla: older microsporocarp, in which the microsporangia have de- 

 veloped to the mother cell stage {mem) and the terminal megasporangium has collapsed. 

 — After Miss Pfeiffer. 



ridium initial; and therefore the male gametophyte, as in Selaginella 

 and Isoetes, is reduced to one vegetative cell (within the microspore) 

 and one antheridium. The antheridium initial begins a series of two or 

 three transverse divisions, after which a central cell is cut off by peri- 

 clinal walls and produces eight sperm mother cells (fig. 405). 



Female gametophyte. — The development of the female gametophyte 

 differs in several important particulars from that of Selaginella and 

 Isoetes. The nucleus of the megaspore divides near its apex and a 

 relatively small apical cell is cut off. The wall thus formed separates 



