GEOLOGICAL HISTORY OF GYMNOSPERMS 41 



RECENT HISTORY 



The existing Coniferales are prevailingly temperate types and 

 form vast forest areas especially in the north. They show a 

 somewhat less southern massing, the two regions being separated 

 by a broad tropical belt united only in the Andean and East 

 Indian regions, but continuous in Tertiary times. 



It is beyond the province of this paper to discuss the recent 

 distribution of gymnosperms but it may be pointed out that this 

 distribution is fully explained by the details of geologic history. 

 The present occurrences of such genera as Tumion, Libocedrus 

 and Callitris are readily understandable if their former distribu- 

 tion is taken into the account. The use of the terms endemic 

 and monotypic becomes then singularly inappropriate when 

 applied to genera like Taxodium, Sequoia, Cunninghamia, 

 Cryptomeria, etc. 



The accompanying diagram (fig. 2) furnishes a graphic sum- 

 mary of the foregoing discussion, illustrating not only the filia- 

 tion of the principal types of gymnosperms, but also their relative 

 abundance during the different eras. 



