LIFE HISTORY OF A FERN 



103 



FIG. 49. Diagram of a young Prothallus 

 (pth.) formed by Germination of a 

 Fern Spore. 



rh., rhizoid or root hair; sp.c., spore coat. 



If one of them alights on a suitable spot, in a moist and shady 

 situation, it may germinate (Fig. 49). Its thick outer wall rup- 

 tures and a delicate tube is 

 put forth, containing the pro- 

 toplasm and nucleus. Cell- 

 division takes place and results 

 presently in the formation of 

 the gametophyte. 



The gametophyte of the 

 fern (Fig. 50) is known as a 

 prothallus. It is an indepen- 

 dent, self-supporting plant, 

 but much less highly orga- 

 nized than the sporophyte, consisting usually of a green, heart- 

 shaped plate of cells, not more than perhaps a quarter of an 

 inch in diameter, and attached to the substratum by delicate 

 hair-like rhizoids. It develops no vascular system but never- 

 theless obtains its food 

 in the same way as the 

 sporophyte, absorbing 

 water containing dis- 

 solved mineral salts 

 from the soil by means 

 of its rhizoids, and 

 splitting up carbon 

 dioxide, obtained from 

 the air, by aid of its 

 chlorophyll. Such pro- 

 thalli are frequently 

 to be found attached to 

 the surfaces of flower- 

 pots and walls in damp 

 greenhouses and other 

 places where ferns are 

 grown. 



The sexual organs, 

 male antheridia (Fig. 

 50, an) and female archegonia (Fig. 50, ar), are, like the rhizoids, 

 found on the lower surface of the prothallus, both usually occurring 

 on one and the same plant, which is therefore mono3cious or 

 hermaphrodite. The antheridia (Fig. 51, a) are essentially similar 



FIG. 50. The Gametophyte Generation or Pro- 

 thallus of a Fern, Aspidium filix mas, X 8. 

 (From Strasburger.) 



A, lower surface of a sexually mature prothallus, showing 



antheridia (an), archegonia (ar), and rhizoids (rJi). 



B, an older prothallus with the young sporophyte genera- 



tion or fern plant (b, w) attached to it. 



