312 



SUPREMACY OF THE SPOROPHYTE 



true in the fern is the large development and complex character 

 of the plant (Fig. 213). This is due to a more efficient absorb- 

 ing and conducting apparatus, the root and vascular bundles. 

 This conducting system was foreshadowed in the elongated cells 

 that appear in the sporophyte of Anthoceros and of the mosses. 

 Here the elongated cells are much more specialized and are united 

 into large bundles, termed the vascular bundles, that appear in 

 the leaves as "veins" and in the stems they are variously related 

 and often constitute a conspicuous portion of these organs, as 

 is the case in the higher plants, see page 76. The fern plant does 

 not correspond to the moss plant. It is the sporophyte which has 

 become independent of the gametophyte. The sexual generation 

 is a small thallus, commonly called the prothallium, that is quite 

 as primitive as the simplest Jungermaniales. Its chief function is 

 the formation of gametes (page 282) and it is capable of nourish- 

 ing the sporophyte only for a short time in the majority of ferns 



Fig. 214. The thalloid gametophyte or prothallium, p, of a fern from 

 which a young fern plant is being developed. This sporophyte has already 

 developed two roots, r, that penetrate the soil, and two leaves, /, are ap- 

 pearing, thus making the fern at an early age independent of the gameto- 

 phyte; rh, rhizoids. 



(Fig. 214). The gametophyte of the Bryophyta never attained 

 any considerable proportions owing to its inability to vary and 

 produce adequate absorbing organs and conducting tissues. 

 This naturally limited the development of the sporophyte which 



