634 



A TEXTBOOK OF THEORETICAL BOTANY 



the Fern, two types of prothalli are formed, one bearing the male, and one 

 bearing male and female sex organs, but both types are free-living and are 

 not attached to their respective spores, as in the case of Selaginella. In 







\/ 



A BCD 



Fig. 644. — Development of the strobiloid condition from the 

 Psilophytalean condition. A, Psilophyton with separate 

 dichotomous sterile and fertile telomes. B, Asterocolamites. 

 Sterile and fertile telomes in mixed whorls. C, Equisetum. 

 Fertile telomes grouped in whorls to form a terminal strobilus. 

 D, Calatnites. Sterile and fertile whorls of telomes alternating. 

 {After Zimmeimonn.) 



Fig. 645. — Hyenia elegatis. A Devonian type with fertile 

 telomes grouped terminally, showing an approach to 

 the Equisetum condition. Note that the ends of the 

 fertile telomes are recurved so that the sporangia are 

 pendant. (After Krausel and Weyland.) 



