SEED-BEARING PLANTS 



411 



364. Distribution. — The cycads and their relatives are 

 all tropical or subtropical. Four genera {MicrocycaSy 

 Zamia, Ceratozamia, Dioon) occur in the western hemi- 

 sphere, with the chief center of distribution in Mexico; 

 and five genera {Cycas, Bowenia, Macrozamia, Encephal- 

 artos, and Stangeria) in the eastern hemisphere, with 



Fig. 303a. — Wilhelm Hofmeister (1824-1877). His comparativ^e studies 

 of the history of development of mosses, vascular cryptogams, and seed- 

 bearing plants, disclosed the fact of an alternation of generations through- 

 out those forms, and afforded the basis for a correct interpretation of the 

 genetic relationship of the great groups of plants. 



the chief center of distribution for the first three in Queens- 

 land, Australia. Encephalartos and Stangeria are confined 

 to Africa. 



