444 PTERIDOPHYTES (FERN PLANTS) 



established in tlie soil and readies maturity, strobili are produced 

 and thus the life cycle is completed. Thus besides having an 

 independent complex sporophyte, the Selaginellas protect their 

 gametophytes and this is an additional adjustment to the land 

 habit. 



Summary of Pteridophytes. — They present a number of 

 features characteristic of Seed Plants. They have an inde- 

 pendent sporophyte with well developed roots, stems, and leaves, 

 which in general have the same tissues that are characteristic 

 of these organs in Seed Plants. The second important feature 

 is the differentiation of vegetative and spore-bearing tissues. 

 This gave rise to the strobilus which is regarded as the forerunner 

 of the flower. The third important feature is the introduction 

 of heterospory and the production of gametophytes within the 

 spore wall. Heterospory and dependent gametophytes made the 

 origin of the seed possible. The fourth feature is the retention 

 of the female gametophyte within the megasporangium during 

 fertilization. This also is a seed-like feature. 



