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 
B 
Fic. 395.— The gametophytes and young sporophyte of Selaginella. 4, 
a megaspore containing a female gametophyte with the portion bearing the 
archegonia exposed by the slit-like opening in the spore wall (Xx 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 wali 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 irtto 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 
