102 JOURNAL AND PROCEEDINGS 



trees and shrubs become incapable of existence and only small 

 perennials which are safely covered up by snow during the 

 long winter are able in the brief summer to expand their 

 flowers and ripen their seeds. 



In looking at the vegetable covering of the earth it is 

 easy to see that it must have always been separable into three 

 great latitudinal zones — two belonging to the north and south 

 hemispheres respectively, and one dividing them lying be- 

 tween the tropics. 



Of course it must be borne in mind that these zones of 

 plant life are hypothetical, and that the precise northern and 

 southern limitations must have varied with changes in the 

 earth's climate. The intermixture of diverse flora must now 

 have become very complicated, but evidently ancient. 



The northern flora is characterized by its needle-leaved 

 Conifera, its catkin-bearing trees and shrubs, and other forest 

 trees, deciduous in winter, and its vast assemblage of herba- 

 ceous types such as the Ranunculacse, Crucifeiae, etc.; these 

 spread over a great part of North America, Northern and 

 Central Asia and Europe. This has been divided into that 

 of the Old and New World by the severance of North 

 America from North Asia, and by the barrier to an interchange 

 of vegetation in the upheaval of the Rocky Mountain Range. 

 Nevertheless its marked continuity requires it to be treated 

 as a whole. 



According to one authority the essential types of the 

 present tree flora, of North America are indicated in the 

 Cretaceous rocks of this country, and becomes more distinct 

 and more numerous in the Tertiary, and because of this, it is 

 maintained that the origin of the North American flora is 

 American. 



The analogy between the Miocene flora of Central 

 Europe and the present North American florals unquestioned, 

 and is greater than between the same fossil flora and that 

 now existing in Europe. 



Those who hold this view believe that the American 

 element in the vegetation of Europe at this period was deriv- 



