THE GAMETOPHYTE OF THE FERN 



315 



a high point of development in 

 the horsetails and club mosses, 

 and becomes even more con- 

 spicuous in the seed plants, as 

 will appear later. 



308. The gametophyte of the 

 fern. The fern spore germinates 

 readily on moist surfaces and 

 puts forth a delicate filament, 

 consisting of a row of cells (Fig. 

 277, A). Several oblique cell 

 walls at the end of this filament 

 cut out a triangular apical cell 

 (Fig. 277, B, x), which becomes 

 the growing point. The final de- 

 velopment is usually a small, 

 delicate, heart-shaped, thallus- 

 like body resembling a small 

 liverwort, but only one cell in 

 thickness, except in the middle 

 region. The apical cell (Fig. 277, 

 C, x) generally becomes situated 

 in a deep notch at the forward 

 end (Fig. 277,D) because of the 

 greater cell growth on either side. 

 The back part of the structure 

 becomes fastened to the earth by 

 numerous delicate filaments or 

 rhizoids which act like root hairs. 

 This structure develops the sex- 

 ual organs of the fern and is con- 

 sequently the gametophyte gener- 

 ation in the life history. It is called 



FIG. 276. The sensitive fern (Onoclea 

 sensibilis) 



the prothallium because it pre- Showing vegetative leaf and spore leaf 



(sporophyll) rising from the creeping 



cedes the fern plant (sporophyte). rootstock 



