SEED-BEARING PLANTS 411 



364. Distribution. The cycads and their relatives are 

 all tropical or subtropical. Four genera (Microcycas, 

 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. 3030. Wilhelm Hofmeister (1824-1877). His comparative studies 

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

 bearing plants, disclosed the fact of an alternation of genera tions^ 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. 



