GEOGRAPHIC DISTRIBUTION OF GYMNOSPERMS 177 



Actinostrobus (2 spp.). It will be noted that these restricted 

 genera are well distributed among the great groups, and that 

 many of them are monotypic. It should be remarked that 

 in the Australasian region are included the principal East 

 Indian and Polynesian Islands. Many of these genera are 

 known to have had formerly a very extensive range, but why 

 the two regions cited, together constituting practically the west- 

 ern coast region of the Pacific, should have proved so favorable 

 for the preservation of types otherwise extinct is an interesting 

 question. 



The other regions of endemic genera are ^orth America, 

 with Sequoia and Taxodium] and South America, with the 

 monotypic Saxogothaea of the mountains of Patagonia. 



Throughout the northern hemisphere the dominant and wide- 

 ly distributed genera are Pinus (70 spp.), Juniperus (30 spp.), 

 Abies (20 spp.), Picea (12 spp.), Cupressus (12 spp.), Larix 

 (8 spp.), and Taxus (8 spp.). There is. also a remarkable pair- 

 ing of western iSTorth America and eastern Asia in the display 

 of certain genera, those common to both regions, besides the gen- 

 era which extend broadly over both hemispheres, being Torreya, 

 Tsuga, Pseudotsuga, Thuja, Libocedrus, and Chamaecyparis. 



The distribution of forms in the southern hemisphere is 

 modified by the fact that temperate conditions occur in three 

 great isolated areas, although this has not resulted in as com- 

 plete a separation of genera as might have been expected.. The 

 dominant Podocarpus (40 spp.) is the only genus which occurs 

 in all three of the south temperate regions ; but in the display 

 of certain other genera there is a pairing of the continents, the 

 Australasian region always being one member of the pair, and, 

 with one exception, South America being the other member. 

 For example, Fitzroya (2 spp.), Libocedrus (8 spp.), Dacry- 

 dium (12 spp.), and Araucaria (10 spp.) are common to the 

 Australasian region and South America; while Callitris (15 

 spp.) is common to the Australasian region and Africa. The 

 occurrence of Callitris in the Mediterranean region of Africa, 

 however, suggests a comparatively recent connection with the 

 Australasian region through the northern border region of the 

 Indian Ocean. 



In considering the distribution of the great groups of Coni- 

 fers one is struck by their somewhat rigid geographic limitation, 



