The Pteridophytes 



493 



Megasporangium + female prothallus + embryo 



Part of ist sporophyte + (gametophyte) -|- (2d sporophyte) 



Seed coat -f endosperm (as 



in conifers) -|- embryo 



> = a seed 



Fig. 306. Selaginella: A, vegetative branch with terminal cone; B, longitudinal section 

 of cone, showing microsporangia on one side, megasporangia on the other ; C, female gameto- 

 phyte protruding from the megaspore wall with several archegonial openings among the 

 rhizoids; D, male gametophyte within the microspore wall; E, male gametophyte with' 

 sperms formed in the cells ; F, section of female gametophyte, or prothallus, after fertiliza- 

 tion, showing two embryos. {After Frank.) 



Summary. The occurrence of conductive tissues in the sporo- 

 phyte of the Pteridophytes not only made possible the develop- 

 ment of large land plants with roots, stems, and leaves, but it 

 gave the sporophyte generation possibilities of evolution far 

 beyond that of the gametophyte. 



The three phyla, ferns, equisetums, and lycopods, all have inde- 

 pendent thalloid gametophytes. . In the ferns they are auto- 

 phytic and bisexual ; in the equisetums, autophytic and usually 

 bisexual ; and in the lycopods, partially saprophytic, sometimes 

 bisexual (Lycopodium) and sometimes unisexual (Selaginella). 



