FOX HILLS AND LOWER MEDICINE BOW 25 



9 leaf-count dominants is recorded from lcss than 4 of thc 6 locahties. On the 

 other hand therc are 2 species, Quercus viburnifoUa and Cinnamormim ajjine, which 

 are more common in distribution than in individual abundance. 



LEAF CHARACTERS 



An analysis of certain structural characters of modern dicotyledonous lcaves 

 of a given area can, with reasonable accuracy, be utihzed to indicate the environ- 

 mental conditions of growth. Bailey and Sinnott ' have studied such leaf charac- 

 ters as size, venation, and margin in fioras of the various chmatic zones of the world 

 and have shown that therc is, in the first place, a gradual increase in the proportion 

 of entire-Ieaved dicotj^ledons from the forests of the cold temperate zone southward 

 into the warm temperate, subtropical, and tropical zones. A few of their repre- 

 sentative areas are shown in the following list : 



Per cent 

 entire-leaved 

 Cold temperate zone: 



Central Russia 28 



East-central North America 28 



France 44 



Warm temperate zoi\e: 



East-central China 48 



Southeastern United States 49 



Los Angeles region 54 



Subtropical and tropical zone: 



Hongkong 71 



Bombay 72 



West Indies 76 



Florida 83 



Malay States 86 



Sinnott and Bailey also pointed out that large leaves, compound leaves, and pin- 

 nate leaves are most abundant in the lowland tropics and decrease proportionately 

 into the subtropical and temperate zones.^ 



The application of several of these criteria to fossil floras was suggested and 

 attempted by Bailey and Sinnott with considerable success. Among others, the 

 early Tertiary Florissant and Green River floras of the Rocky Mountains, with 

 33 and 29 per cent, respectively, of entire-margined leaves appeared to indicate 

 temperate conditions. In contrast, the Eocene Wilcox flora of the Gulf coast, with 

 83 per cent of entire-margined leaves, indicated subtropical conditions. These 

 general conclusions have been amply corroborated by the studies of the genera and 

 species of the several floras in question. Chaney and Sanborn ^ have more recently 

 applied similar criteria to the Eocene Goshen flora of Oregon, and have added the 

 textural character and the presence or absence of a dripping point as useful leaf 

 characters for the determination of climatic conditions. Their conclusion that 



' Bailey, E. W., and Sinnott, I. W., Science, n. s., vol. 41. 832, 1915. 



«Sinnott, I. W., and Bailey, E. W., .\mer. Jour. Bot., vol. 2, table I, 1915. 



' Chaney, R. W., and Sanborn, E. I., Carnegie Inst. Wash. Pub. No. 439, 18, 1933. 



