Chapter X 



-177— 



Historical Causes 



taceous period New Guinea and New Zealand constituted the periphery 

 of Australia. Not until the Tertiary period did they break away from 

 Australia and drift off into the Pacific Ocean. The isolation of Aus- 

 tralia, thus, presumably took place during the Tertiary period. At the 

 beginning of the Cretaceous period it was still connected, by way of 

 Madagascar and India, with southern Asia. The Andes of Antarctica 

 constitute a continuation of the Andes of South America. The drift- 

 ings of the continents induced changes in their position relative to the 

 poles; this, in turn, led to changes in climatic zonation and, conse- 

 quently, to changes in the distribution of living organisms. 



^ Fveoptarisflora 



O Olosaopterisflcra ohne QtoBsopteris 



.f L«pido<leDdrooflora 



IS) Olotaoptahiflora 

 ^ .A. Mi30UloreD 



Fig. 24. — Distribution of floras and location of the equator during tlie Carboniferous and 

 Permian periods. (After Koppen and Wegener). 



On the basis of the foregoing assumptions riddles that formerly 

 seemed insoluble in the past and present geographical distribution of 

 organisms are solved. Among such riddles we may mention, first, the 

 distribution of plants and even of entire floras in zones that, as regards 

 their present climatic conditions, are not suitable to these plants, and, 

 second, uniformity of vegetation, indicating that formerly there existed 

 uniform climatic conditions in regions where at present there are 

 marked differences in climatic and vegetation zones. 



Another such riddle that long seemed insoluble is the absence in the 

 Carboniferous period of periodicity in plant growth. In the case of our 

 present-day plants this periodicity is expressed by the alternation of 

 active periods {i.e., periods of intensive growth and development) and 

 dormant periods (during that part of the year when climatic conditions 

 are unfavorable). One of the characteristic features of such periodicity 

 is, for instance, the possession by deciduous and coniferous trees and 



