THE EVOLUTION OF PLANTS 



607 



features that characterize the Cycadofilicales, their 

 development of a bisporangiate strobilus with two sets 

 of sporophylls, related to one an- 

 other as they are in the flower of 

 the Angiosperms, indicates a gen- 

 etic relationship to that group, as 

 does also the fact that the seeds, 

 enclosed in a fruit, possess a dicot- 

 yledonous embryo, without endo- 

 sperm. In other features the Ben- 

 nettitales are unlike the Angio- 

 sperms; the ovules, for example, 

 are enclosed by sterile scales, in- 

 stead of by the carpels on which 

 they are borne, and the protrusion 

 of the pollen-chamber through the 

 micropyle signifies the gymno- 

 spermous type of fertilization. 



These and other comparisons in- 

 dicate that the Bennettitales were 

 essentially Gymnosperms having 

 certain Angiospermous characters, 

 and therefore, while they are not 



to be considered as the ancestors Fig. 429.— Magnolia. 



. . . Flower with perianth re- 



of the Angiosperms, it is probable moved, showing the com- 



that they and the modern dicoty- P^^^f ^^^^.f ^^Ve'st! 



ledons are both descended from a mens have been removed. 

 , 1 r .1 .1 Note their spiral arrange- 



■ common branch of the ancestral j^e^t as shown by the scars 



tree. Among modern plants, the at the points of attachment. 



. , X ,. . (Cf. Fig. 428.) 



flower of the magnolias most 



closely resembles that of Cycadeoidea in the spiral arrange- 

 ment of its stamens and pistils (Figs. 428 and 429.) . How 



