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. 384). 
The gametophyte resembles the thallus of the 
> simplest Liverworts. When mature it has a 
Fre. 384.— cushion-like central axis where the rhizoids and 
Three Fern  gex organs are developed, and wing-like margins 
gametophytes ¢onsisting of a single layer of cells. The game- 
shown about : A 
Se 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 
Fic. 386.— A Fern 
Fic. 385.— An enlarged view of the gametophyte (g) bearing 
under surface of a Fern gametophyte, a young sporophyte (s) 
showing the archegonia (a), the antheridia with leaf at J and root 
(b), and the rhizoids (r). at r. 
damp walls, damp soil, and on the sides of flower pots. Oc- 
easionally 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 
