GAMETOPHYTES 



443 



the young sporophyte until it becomes self-supporting. The 

 female gametophyte therefore consists of many cells when mature 

 and bears a number of archegonia on the portion exposed by the 

 opening forced in the spore wall by the expansion of the game- 

 tophyte. 



Previous to fertilization, the male gametophytes, each still, 

 except for a small slit-like opening, encased in the wall of the 



FIG. 395. The gametophytes and young sporophyte of Selaginella. A, 

 a megaspore containing a female gametophyte with the portion bearing the 

 archegonia exposed by the slit-like opening in the spore wall (X 100). B, 

 section through a megaspore, showing the spore wall (w) and female game- 

 tophyte (g) with one archegonium (a) with neck and egg (e) visible (X 100). 

 C, a section through an antheridium, showing the small prothallial cell at the 

 base and the wall cells which enclose the sperms within, one of which is shown 

 fully mature at the left ( X 500) . D, a young sporophyte with stem at s and 

 root at r and foot extending into the gametophyte which is still enclosed in 

 the spore wall (m) . From Atkinson and nature. 



microspore, fall out or are blown out of the microsporangia, which 

 open when the spores are mature, and fall or are carried by the 

 wind to the megasporangia where the female gametophytes are 

 developing. Here the sperms escape, and reach the archegonia, 

 which are accessible through the slit-like openings in the walls of 

 the megasporangia and megaspores. The fertilized egg develops 

 immediately into a sporophyte. Often the female gametophyte 

 remains in the megasporangium until the weight of the young 

 sporophyte tumbles it out. After the young sporophyte becomes 



