PTERIDOPHYTES 



111 



break through the wall of the microspore and develop a free 

 plant (Fig. 90). When it is remembered that whatever a 

 microspore produces must be a male gametophyte, no matter 

 what it looks like, this small group of cells within the micro- 

 spore must be the male gametophyte. When the group is 

 examined, it is discovered that there is a single antheridium, 

 with its wall in- 

 closing sperm- 

 producing cells. 

 This represents a 

 gametophyte that 



FIG. 90. Selaginella: 

 the male gametophyte 

 completely developed 

 within themicrospore ; 

 the group of squarish 

 cells with nuclei are 

 those that produce 

 sperms. After Miss 

 LYON. 



FIG. 91. Selaginella: the female gametophyte 

 within the megaspore, but having burst 

 through on one side : m, megaspore wall ; a, 

 archegonium ; r, rhizoid. 



has disappeared from ordinary sight, and that can be 

 discovered only by the microscope. 



When a megaspore germinates, there appears within it 

 a much larger group of cells than appears in the microspore 

 (Fig. 91), for the megaspore is much larger than the micro- 

 spore. But even this larger group of cells does not free itself 

 from the megaspore wall and grow into a free plant ; but 

 it does develop archegonia, and must be the female gameto- 

 phyte. 



In heterosporous plants, therefore, the two gametophytes 



