PTERIDOPHYTA 



297 



tissue is developed and only one archegonium is formed. At the apex 

 of the megaspore, where the wall is relatively thin, there is a papilla 

 filled with dense cytoplasm in which the nucleus lies (Fig. 253^1). When 

 the spore germinates, the nucleus divides and a small cell is cut off 

 by a transverse wall (Fig. 253/^). The rest of the garnet ophyte acts as a 



G H I J 



Fig. 252. Male gametophyte of Marsilea quadrifolia. A, microspore with starch grains 

 in cytoplasm; B, prothallial cell cut off; C, microspore divided into two antheridium initials, 

 in each of which a jacket cell is being formed; D and E, additional jacket cells being cut off; 

 F, two primary spermatogenous cells enlarging; G, H, I, stages showing increase in sperma- 

 togenous cells to sixteen in each of the two antheridia; /, mature sperm, X 1,200; other 

 stages, X350. {After Sharp.) 



food reservoir. The small cell is the archegonium initial, the larger one 

 the nutritive cell. As development proceeds, the archegonium breaks 

 through the megaspore wall. The mature archegonium consists of a 

 large egg, a small ventral canal cell, a small neck canal cell, and a sterile 

 jacket (Fig. 253/)). The neck is short, consisting of only two tiers of four 

 cells each. Mucilage above the archegonium forms a deep funnel into 

 which the sperms collect. 



Embryo. In the development of the embryo, the first wall is vertical, 

 as in the Filicales, and then a quadrant stage appears (Fig. 2oZE). The 



