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 perinium 

 (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- 



mcm 



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 



