DEVELOPMENT OF PLANTS 



331 



ous rhizoids (Fig. 228). This gametophyte often becomes heart- 

 shaped (Fig. 228, C), owing to the more rapid growth of the 

 cells that are cut off from the apical cell. In some genera 

 branched filamentous or narrowly thalloid growths are developed 

 that resemble the protonema of the mosses or the thallose hepat- 



Fig. 228. Fig. 229. 



Fig. 228. Gametophyte of the Filicales: A, germination of the spore. 

 B, early appearance of the thalloid structure of the gametophyte owing to 

 the formation of an apical cell, x. C, mature gametophyte — an, antheridia; 

 ar, archegonia: r, rhizoids; v, apical cell or growing point. 



Fig. 229. Structure in reproductive organs: A, antheridium as seen in 

 section, just before the discharge of the gametes. B, male gamete. C, 

 section view of archegonium — g, female gamete. 



ics. The gametophyte usually lives but a few months, although 

 in some species they may endure for years, multiplying exten- 

 sively by gemmae, and so form conspicuous mats upon the moist 

 trunks and rocks. The archegonia and antheridia are usually 

 borne upon the same gametophyte. Some genera, however, are 



