6 FERNS IN THEIR HOMES AND OURS. 



antheridia, which are situated rather more than 

 half way between the little notch or sinus at the 

 upper edge of the prothallus and the lower edge. 

 They consist of cells more rounded than the rest, 

 and which contain still other and smaller cells. 

 Each of these last contains, in its turn, one spirally- 

 coiled antherozoid (see PI. 3, Figs. 10-12). When 

 the antherozoids are perfected, the enveloping cells 

 burst, and they are set free. They are the male 

 element, analogous to the pollen of flowers. II. 

 The archegonia, or those organs which are analo- 

 gous to the pistils of flowers with their ovaries, 

 are usually less numerous than the antheridia, and 

 are situated nearer the sinus of the prothallus (PL 

 3, Figs. 13-14). They consist of cells so arranged 

 as to form a tube around a central cell, which is 

 called the oosphere, and is the point to be fertilized 

 and produce the plant-bud. The outer end of the 

 tube remains open till fertilization has taken place, 

 after which it closes. In the particular species 

 we have chosen for observation, the antheridia 

 and archegonia are usually on the same prothallus : 

 but in some species the male and female organs 

 are on different protkalli ; or, at least, not per- 

 fected at the same time on the same one. This 

 renders cross-fertilization occasionally necessary 

 in this class of plants, and shows the possibility 

 of finding hybrid ferns, of which, as stated in the 

 next chapter, our Asplenium ebenoides is by many 



