432 



PTERIDOPHYTES (FERN PLANTS) 



end is first produced. The development of this tube, called germ 

 tube, is germination. The germ tube soon reaches its full length, 

 and then it begins to broaden at the outer end and a tiny, green, 

 heart-shaped gametophyte is produced (Fig. 38Jf). 

 The gametophyte resembles the thallus of the 

 simplest Liverworts. When mature it has a 

 cushion-like central axis where the rhizoids and 

 sex organs are developed, and wing-like margins 

 consisting of a single layer of cells. The game- 

 tophyte is called a prothallus, the term referring 

 to the fact that it is thallus-like in form and 

 precedes the sporophyte in reproduction. In and around Fern 

 beds in greenhouses Fern gametophytes are quite common on the 



FIG. 384. 

 Three Fern 

 gametophytes 

 shown about 

 natural size. 



' 



FIG. 385. An enlarged view of the 

 under surface of a Fern gametophyte, 

 showing the archegonia (a), the antheridia 

 (6), and the rhizoids (r). 



FIG. 386. A Fern 

 gametophyte (g) bearing 

 a young sporophyte (s) 

 with leaf at I and root* 

 at r. 



damp walls, damp soil, and on the sides of flower pots. Oc- 

 casionally they can be found out of doors about Ferns growing 

 in moist shady places. They lie flat on the substratum, and the 

 sex organs are borne underneath where there is moisture for the 



