PTERIDOPHYTA 



289 



The antheridia of the Filicales differ greatly in development from those 

 of the lower pteridophytes (Fig. 245). The initial is superficial and papil- 

 late. The first wall is transverse, the antheridium developing from the 

 outer cell. This then undergoes a second transverse division, cutting off a 

 basal ring cell. Due to increasing turgidity of the upper cell, the wall 

 formed, called the funnel wall, becomes concave and approaches the first 



Fig. 244. Ventral view of a fern prothallium (Polypodiaeeae), showing rhizoids and nu- 

 merous antheridia in the older portion and three archegonia near the growing notch, X 35. 



wall, finally touching it (Fig. 245^). Next a do7ne wall appears, delimit- 

 ing an outer cell from a central cell (Fig. 2455). The dome wall is hemi- 

 spherical and nearly concentric with the outer surface of the antheridium. 

 The appearance of a second funnel wall in the outer cell results in the for- 

 mation of another ring cell and a cap cell, thus completing the sterile 

 jacket (Fig. 245C-£'). The output of sperms in the higher families is 

 commonly 32. As in the other ferns, the sperms are large, coiled, and 

 multiciliate (Fig. 245F). 



The archegonia appear late in the development of the gametophyte, 

 thus occurring in the median portion near the growing notch (Fig. 244). 



