THE GAMETOPHYTE OF THE FERN 



317 



single cell which projects above the surface of the prothallium. 

 There are only three cells forming the capsule of this structure, 

 a cover cell above, a ring-shaped cell in the middle, and a 

 funnel-shaped, basal cell These three cells inclose at first a large 

 central protoplast, from which is developed a group of one hun- 

 dred or more small cubical cells 

 that produce the sperms, as in the 

 bryophytes. These sperms are, how- 

 ever, very different in form from 

 the two-ciliate sperms of the liver- 

 worts and mosses and many algae. 

 Each consists of a spirally coiled 

 band (Fig. 278, D), whose narrower- 

 pointed end is covered with numer- 

 ous cilia, making it a many-ciliate 

 sperm. 



The archegonia. The archegonia 

 of the ferns are also much smaller 

 than those of the bryophytes and 

 simpler in structure. The short neck 

 alone projects above the surface 

 of the prothallium (Fig. 277, E) 

 and generally bends backward, 

 probably because the forward part 

 of the prothallium is not directly 

 on the earth, but rises at an angle. 

 The egg lies beneath the surface of 

 the prothallium, so that the base 

 of the archegonium may be described as sunken. There are 

 only two or three canal cells (Sec. 283) in this archegonium. 



The eggs are fertilized under exactly the same conditions as 

 hi the bryophytes (Sec. 283). When the prothallia are wet the 

 sexual organs open, and the sperms swim over the moist surfaces 

 and are attracted to the necks of the archegonia by substances 

 secreted within, one of which at least is malic acid. The 



FIG. 278. The antheridium and 

 sperms of a fern (Onoclea) 



A, small prothallium with many 

 antheridia an : s, old spore wall. 

 B, antheridium, showing cover 

 cell c, ring cell r, and basal cell 

 6, inclosing the sperm mother 

 cells. C, antheridium opening. 

 D, sperms. After Campbell 



