444 PTERIDOPHYTES (FERN PLANTS) 
established in the soil and reaches 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. 
