PTERIDOPHYTES 



'37 



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. 309, 310. Archegonium of 

 Sclaginella: 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 

 FIGS. 31 1-3M. -Embryo of Selagindla: develops the stem, flanked by 



31 1, 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 foot 1S develope< (tig. 



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 BRUCHMANN; 

 312-314, after PFEFFER. 



311 



two cells (one on each side) 

 that develop leaves. From 

 one of the leaf segments the 



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 



