THE EVOLUTION OF PLANTS 



607 



features that characterize the Cycadofilicales, their 

 development of a bisporangiate strobilus with two set 

 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 

 of the Angiosperms, it is probable 

 that they and the modern dicoty- 

 ledons are both descended from a 

 common branch of the ancestral 

 tree. Among modern plants, the 

 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 



Fig. 429. — Magnolia. 

 Flower with perianth re- 

 moved, showing the com- 

 pound pistil, and four of the 

 stamens. Most of the sta- 

 mens have been removed. 

 Note their spiral arrange- 

 ment as shown by the scars 

 at the points of attachment. 

 (Cf. Fig. 428.) 



