DEVELOPMENT OF PLANTS 



283 



ture 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 bundle, 

 which are essentially of the same character as in the higher plants. 

 Furthermore, this 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, com- 

 monly called the prothallium, that is quite as primitive as the 

 simplest Jungermaniales. Its chief function is the formation of 

 gametes (page 254) and it is capable of nourishing the sporo- 

 phyte only for a short time in the majority of ferns (Fig. 214). 

 The gametophyte of the Bryophyta never attained any consider- 

 able proportions owing to its inability to vary and produce ade- 

 quate absorbing organs and conducting tissues. This naturally 

 limited the development of the sporophyte which was parasitic 

 upon it. In the Pteridophyta, however, the sporophyte is not 

 at such a disadvantage since it actually becomes independent of 



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, I, are ap- 

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

 phyte, rli, rhizoids. 



the gametophyte owing to the development of a root which puts 

 it in communication with the earth substances. This radical de- 



