342 



BOTANY OF THE LIVING PLANT 



on different prothalli (Fig. 284, i). In the former case the antheridia, 

 or male organs, commonly appear first, and the archegonia, or female 

 organs, later. There may thus be a separation of the sexes either in 

 time or in space. The flattened prothallus of the ordinary cordate type 

 (Fig. 283) usually bears both sex-organs. When grown under normal 

 circumstances on a horizontal substratum it produces them on its 



FIG. 283. 



Matureprothallus of Nephrodium Filix-mas, as seen from below, bearing antheridia 

 among its rbizoids, and archegonia near to the apical indentation. (After Kny.) 



lower surface, the antheridia in the basal or lateral regions, the arche- 

 gonia upon the massive cushion. The latter develop in acropetal 

 order, the youngest being nearest to the incurved apex of the 

 prothallus. The position of the sexual organs is evidently favourable 

 to their continued exposure to moist air, or to fluid water which 

 is necessary for carrying out their function. 



The antheridium, which arises by outgrowth and segmentation of 

 a single superficial cell (Fig. 284, 2, 3), consists when mature of a 

 peripheral wall of tabular cells, surrounding a central group of sperma- 

 tocytes (Fig. 284, 4, 5). The antheridium readily matures in moist air, 



