PTERIDOPHYTES 
137 
spore walls are brought to the mega- 
sporangia by the wind or by gravity. 
The microspores drift among the 
megaspores with protruding female 
gametophytes bearing archegonia. 
Then the sperms are discharged, 
enter the archegonia, and fertiliza- 
tion occurs (fig. 310). In these 
female gametophytes, still in the 
sporangia, the embryo sporophytes 
develop and then emerge, a strobilus 
311 
FIGS. 311314. Embryo of Sclaginella: 
311, first division of fertilized egg (the outer cell 
to form the suspensor, the inner cell to form the 
embryo); 312, early stage of the embryo (at- 
tached to suspensor), the apical cell of the stem 
being evident; 313, later stage of the embryo, 
showing (to the right) the apical cell of the stem 
between the apical cells of the first two leaves 
and (to the left) the developing foot; 314, an 
older embryo, showing the foot (to the right 
below), the root (to the right above), the sus- 
pensor, the two leaves (to the left) with their 
ligules, the centrally placed stem tip, and the 
developing vascular system extending between 
Stem and root tips 311, after BECCHMANN; 
312-314, after PFEFFER. 
FIGS. 309, 310. Archegonium of 
Selaginella: 309, the neck and the axial 
row (neck canal cell, ventral canal cell, 
and egg); 310, fertilization, the sperm in 
contact with the egg. - After Miss 
LYON. 
often being beset with young 
sporelings. Later the strobilus 
as a whole, with its attached 
sporelings, drops off. 
Embryo. The embryo 
(sporophyte) is developed 
much as in Lycopodium (figs. 
311-314). The suspensor (p. 
130) is more extensive than 
in Lycopodium, being of use 
in relating the embryo to the 
deep nutritive tissue within 
the megaspore. The em- 
bryonal cell at the end of the 
suspensor first produces three 
cells : a terminal cell that 
develops the stem, flanked by 
two cells (one on each side) 
that develop leaves. From 
one of the leaf segments the 
foot is developed later (fig. 
313); and still later, from the 
same segment the primary 
root arises (fig. 314). When 
fully organized and emerging, 
the embryo resembles a seed- 
ling dicotyledon escaping from 
its seed. The tuberous foot 
