136 MIOCENE CLIMATE. 



similar climate for the Swiss Tertiary district. A still stronger 

 proof is furnished by the numerous forms of plants of the warm 

 zone which constituted the principal portion of the flora of that 

 epoch. The distribution of their homologous living species is of 

 so much importance for the settlement of this question that we 

 shall notice particularly a few of the trees to which we have 

 already referred (see vol. i. pp. 325-331). 



These plants may be divided into two classes namely, those 

 which can support the winters of the temperate zone,, and those 

 which cannot bear that climate and consequently cannot be 

 planted in Switzerland in the open air. Of the first class the 

 following species are nearly allied to widely distributed Miocene 

 trees the swamp-cypresses, the Sequoiee and Glyptostrobi, the 

 liquidambars, the Italian date-plum (Diospyros), and the tulip- 

 tree. All these trees are natives of the warm zones ; but yet 

 they thrive in the plantations of Central Europe, although most 

 of them do not ripen their fruit here, showing that in this region 

 the extreme limit is attained of their artificial area of distribu- 

 bution. They do not flourish in a temperature lower than 

 46-4 Fahr. (or 8 Cent.). Thus we find that the tulip-tree 

 regularly blooms near Zurich, but rarely forms germinable 

 seeds ; in North Germany it seldom blooms, and in the north of 

 Prussia (as near Stettin) it is killed by cold winters ; on the 

 coast of the Baltic (as near Dantzig) it can no longer bear the 

 climate, any more than that of Kiev in Russia, where the mean 

 January temperature is 6'2 Cent, (or 20'8 Fahr.). In Dub- 

 lin it thrives well and flowers, but without forming seeds ; in 

 the south of England it sometimes produces ripe seeds; but 

 north of Edinburgh it no longer blooms, and does not grow to 

 any size. Hence the temperature of 9 Cent, (or 48 0> 2 Fahr.) 

 may be regarded as the northern boundary-line of this tree. 

 It finds its most luxuriant development in the swamps of the 

 southern United States ; and the gigantic trees which we meet 

 with in the gardens of Madeira prove that it is well suited to a 

 subtropical climate. 



In the second class, viz. plants which cannot support the win- 

 ter of the temperate zone, the camphor-trees, the Japanese 

 cinnamon- tree, the Sapindi, the Proteacese, Celastrea, and jujube- 



