6Q 



THE NATUKAL HISTOKT EEYIEW. 



It is evideut from these considerations, that tropical Africa and 

 America have borrowed little of one another within the period 

 of the creation of the forms of plants now inhabiting each, — 

 that the differences between these Floras are so gi-eat, that it is 

 doubtful whether at any time there has been much community of 

 vegetation,— and that the hypothetical modern Atlantic continent, 

 which Heer assumes to have existed in the North Atlantic, and to 

 have connected Europe and North America, cannot have extended 

 to the south of the Tropic of Cancer. 



If, on the other hand, we compare tropical Africa with tropical 

 Asia, we find, 1, a vast amount of specific and generic identity; 

 2, an absence in Africa of any great or peculiar group, that is 

 not also Asiatic ; and 3, an absence in Africa of many of the great 

 groups that are characteristic of Asia. The sum of these facts 

 amounts to fair evidence, that tropical Africa was peopled by plants 

 from tropical Asia, and that within a comparatively modern epoch. 

 Up to the present time we have no sufficient data for comparing tropi- 

 cal Africa, generically even, with America beyond the West Indies, 

 and until this is done, it would be rash to speculate upon the means 

 whereby the few plants common to tropical Africa and the West 

 Indies have been transported from the one to the other ; or why it 

 is that there should be so many Orders common to America and Asia, 

 that are scantily represented, or totally absent in tropical Africa. 



Turning now from these points of difference between the Floras 

 of the Old and New Worlds to those of similarity, a comparison of 

 the contents of Dr. Grisebach's Flora with those of Mr. Thwaites' 

 enumeration, gives some curious results. 



In the first place, the number of Natural Orders is almost pre- 

 cisely the same in both areas, viz., 156 in Ceylon, and 152 in the 

 West Indies ; and the Ordersf themselves are to a great extent the 

 same ; the Orders not represented in both being, with the exception 

 of six, either small or feebly represented. These are the following : — 



I^resent m 



the West Indies, hut 

 I Ceylon. 



ORDERS. 



PapavcraceaB . 

 Sauvagesiacese 



GEN. 



2 

 1 



SPEC. 



2 

 1 



Present in Ceylon, hut ahsent in 

 the West Indies. 



ORDERS. GEN. SPEC. 



BerberidesB . . 1 1 



*Tamariscineaj . 1 1 



t The respective authors have sh'ghtly different opinions as to the limits of 

 some of the Orders, but these are here reduced to the same standard. 



