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PLANT MORPHOLOGY 



The initial is superficial but remains embedded. It divides transversely, 

 the outer segment being the primary neck cell and the inner one dividing 

 again to form the central cell and basal cell (Fig. 246^, B). The central 

 cell gives rise to the axial row, which consists of a single binucleate neck 

 canal cell, a small ventral canal cell, and the egg (Fig. 2A(dC-E). In the 

 Osmundaceae and Gleicheniaceae the neck canal nuclei may be separated 

 by a wall. The venter of the mature archegonium is embedded in the 



C E F 



Fig. 245. Stages in development of the antheridium of Nephrolepis (A to E), X700, and a 

 sperm of Dryopteris (F), more highly magnified. A, cutting off a basal ring cell by funnel 

 wall; B, appearance of dome wall, delimiting of outer cell from central cell; C, formation of 

 second funnel wall; D, first division of central cell; E, mature antheridium with sperms form- 

 ing in spermatogenous cells. (A to E, after Gilbert M. Smith; F, after Yamanotichi.) 



prothallium, but the neck, which usually curves slightly backward, pro- 

 jects beyond the surface (Fig. 246F). The neck consists of four vertical 

 rows of cells. 



Embryo. The Filicales are characterized by a striking regularity in the 

 early divisions of the embryo. The first division of the fertilized egg is 

 not transverse but vertical, i.e., parallel with the long axis of the archego- 

 nium (Fig. 247A). By a division of each daughter cell at right angles 

 to the plane of the first division, quadrants are formed (Fig. 247B). Of 

 the two inner cells, the anterior one gives rise to the stem and the posterior 

 one to the foot. Of the two outer cells (those nearer the neck of the arche- 

 gonium), the anterior one forms the first leaf and the posterior one the 

 primary root. Thus the arrangement of the quadrants differs conspicu- 

 ously from that found among the eusporangiate ferns. The subsequent 

 divisions are at first regular, resulting in a globular embryo in which the 

 four primary organs may be easily distinguished (Fig. 247C). Later 

 growth, however, is irregular, the leaf and root developing more rapidly 

 and soon breaking through the calyptra (Fig. 247D). 



