PTER1DOPHYTA 



249 



whole antheridium, in the lower or eusporangiate Ferns, develops 

 at once into the mass of sperm-cells, while the outer cell serves as 

 the covering for these (Fig. 235). It is not impossible that this type 

 of antheridium may have been derived from that of the Anthocero- 

 tales by a suppression of the sterile cells of the endogenous anther- 

 idium, whose peripheral cells are replaced by the superficial cells 

 covering the cavity in which the antheridium is situated. 



FIG. 213. Struthiopteris Germanica. Development of antheridium. A-C, vertical 

 sections (x GOO). D, nearly ripe sperm-cells. E, spermatozoid (X1200). 



In the more specialized Ferns (Leptosporangiatae), especially the 

 Polypodiacese, the antheridium (Fig. 213) projects as a nearly spherical 

 body, in which the cell-divisions are very regular. In the Polypo- 

 diacese the hemispherical mother-cell is first divided by a funnel- 

 shaped wall (Fig. 213, A-C), whose smaller end is usually in 

 contact with the basal wall of the antheridium. The next wall is 

 dome-shaped, and its base is in contact with the first-formed wall. 



