832 



SCIENCE 



[N. S. Vol. XLI. No. 1066 



interesting correlations between structural 

 characters and climate. Particularly signif- 

 icant in the consideration of certain problems 

 of geology and climatology is the climatic dis- 

 tribution of two types of leaves and leaflets. 

 Those with entire margins predominate in trop- 

 ical, arctic and alpine regions, moors, steppes, 

 deserts, saline situations, and other physiolog- 

 ically dry environments. (In this connection 

 it should be noted that the leaves of tropical 

 rainforests and other tropical plant commu- 

 nities that live in moist environments, although 

 often of relatively large size, are semi-sero- 

 philous in structure.) Leaves and leaflets with 

 non-entire margins, on the other hand, are 

 comparatively infrequent in such situations, 

 and are very numerous in moist temperate 

 regions having cold winters and warm sum- 

 mers. 



In the following table are given for a num- 

 ber of extensive regions in the frigid, tem- 

 perate and tropical zones the percentage of 

 entire-leaved woody plants in the Dicotyledon- 

 ous flora. ^ 



Per Cent. 

 Enlire 



EUesmeTeland 100 



New Zealand Alps 77 



North East Siberia 65 



Cold Temperate 



North East Germany 24 



Central Russia 28 



East Central North America 28 



North Russia 30 



England 32 



Kamtsehatka 33 



Rocky Mountains 36 



South East Siberia 37 



West Siberia 44 



France 44 



Warm Temperature 



South Russia 39 



East Central China 48 



South East United States 49 



Italy 50 



1 In the computation of the percentages given 

 in this table woody Dicotyledons alone were used 

 since herbaceous forms are of very infrequent oc- 

 currence in the fossil floras of the Cretaceous and 

 early Tertiary. 



Los Angeles Region 54 



Spain 56 



Sub-tropical and Tropical 



Hongkong 71 



South West Asia 72 



Bombay 72 



Upper Nile Region 74 



Southern Africa 74 



Nicaragua 76 



West Indies 76 



Egypt 77 



South East Central Africa 78 



Brazil 79 



Ceylon 80 



Manila 81 



West Central Africa 81 



Queensland 82 



New iSouth Wales 82 



West Australia 83 



Florida 83 



South West Central Africa 83 



MauritiusnSeychelles 85 



Malay States 86 



In the temperate regions given above there 

 are more or less extensive areas of physiolog- 

 ically dry environments which are reflected in 

 the floras by plants with relatively small en- 

 tire leaves. In the tropical regions, on the other 

 hand, there are cool uplands and shady compara- 

 tively temperate habitats which possess many 

 plants with non-entire leaves and leaflets. The 

 effect of these cool uplands upon the character 

 of the foliage is well illustrated by comparing 

 the percentage of entire-leaved Dicotyledons 

 in the mountainous Simla region (58 per 

 cent.) with that of the adjacent Upper Gan- 

 getic Plain (71 per cent.), and also by con- 

 trasting lowland (76 per cent.) and upland (56 

 per cent.) Hawaii. 



In view of these facts it seems desirable to 

 give an analysis of two floras that are more 

 nearly homogeneous phytogeographically. The 

 first flora, cold-temperate mesophytic, was 

 constructed by eliminating from the flora of 

 east central North America (east of the 95th 

 meridian and between the 40th and 50th paral- 

 lels of latitude) all plants growing on physio- 

 logically dry environments. The second flora, 

 tropical, was formed from the woody plants of 

 the moist lowlands of the Amazon valley. 



