SPEHMATOPHYTA 



319 



filicales. The resemblance between the bisporangiate cj^cadeoid cone 

 and the flower of the magnolia and its allies has suggested that the angio- 

 sperms may have been derived from the Bennettitales, but there is little 

 evidence to support this view (see page 411). 



3. Cycadales 



This order includes 9 living genera and about 100 species, all of which 

 are tropical or subtropical in distribution. Four of the genera belong to 

 the Western Hemisphere and five to the Eastern Hemisphere. Zamia, the 



Fig. 267. Dioon edule with a large female cone 28 cm. in diameter. 

 1.5 m. long. 



The leaves are up to 



largest genus, has about 30 species; it ranges from Florida to Chili. 

 Microcycas is confined to w^estern Cuba, Dioon and Ceratozamia to southern 

 Mexico. Cycas, with 20 species, ranges from Japan to Australia and 

 Madagascar. Bowenia and Macrozamia are found only in Australia, 

 Sfangeria and Encephalartos only in Africa. The Cycadales are closely 

 related to the Bennettitales and like them were probably derived directly 

 from the Cycadofilicales. They flourished throughout the Mesozoic and 

 reached their greatest display in the Lower Cretaceous, when they were 

 much more widespread than they are today (Fig. 258). 



Sporophyte. The stems of cycads are either subterranean and tuberous 

 or aerial and columnar. They bear a crowai of large fern-like leaves (Fig. 

 267). The stems of the columnar forms are covered with an armor of 

 persistent leaf bases. The stem is rarely branched and is commonly less 

 than 3 m. high. The tallest species {Macrozamia hopei) sometimes 

 reaches a height of 18 m. The leaves are pinnate (bipinnate in Bowenia) 



