PTERIDOniYTES 



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 



Figs. 31 1-3 14. — Embryo of Selaginella: 

 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 Beuchmann; 

 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 



