CHAPTEK VIII 



GEOGRAPHIC DISTRIBUTION OF GYMNOSPERMS 



ALTHOUGH geographic distribution is not a part of mor- 

 phology, the special student of Gymnosperms should be familiar 

 with the broad outlines of the distribution of the living forms. 

 Xo attempt will be made to trace the historical migrations of 

 the different types, or to indicate natural physiographic areas. 

 It is sufficient to say in general that there is evidence that most 

 of the forms once had a very much more extended range than 

 now, and that the change has consisted chiefly in. a gradual re- 

 striction of the areas occupied. 



CYCADALES 



At present the Cycads are strictly tropical forms, the nine 

 genera, containing something less than one hundred species, 

 being distributed about equally between the oriental and occi- 

 dental tropics. Cycas, the oldest genus, containing about 

 sixteen species, is the most widely distributed oriental genus, 

 ranging throughout tropical Asia, the East Indies, and the Aus- 

 tralian region; while Macrozamia, with fourteen species, and 

 the monotypic Bowenia, are strictly Australasian; Encephalartos, 

 with twelve species, and the monotypic Stangeria, are African. 



In the occidental tropics the largest genus is Zamia, with 

 about thirty species, ranging through tropical and subtropical 

 America; Ceratozamia, with six species, and Dioon, with two 

 species, are Mexican ; while the monotypic Microcycas is Cuban. 



It may be remarked in general that Cycas and Zamia repre- 

 sent the typical Cycads of the two hemispheres, while the other 

 genera represent relatively isolated forms which bear the stamp 

 of local conditions. 



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