350 Count Gaston de Saporta on the Temperature 



plants may be classed in still existing families ; but the Dicoty- 

 ledons are still absent, and the Monocotyledons scarcely make 

 their appearance. The appreciable indices show the existence of 

 a temperature approaching that which prevails in southern 

 countries in the vicinity of the tropics, between 20° and 30° S. 

 lat. This temperature may be estimated at a mean of 20° C. 

 ( = 68° F.). 



The Cretaceous series, starting from its middle stages, con- 

 stitutes a third period, resembling the preceding in certain re- 

 spects, by the persistence of the same genera. Nevertheless the 

 Cycadese begin to decline, the Pandanese and the Palms are de- 

 veloped, and, lastly, the Dicotyledons make their appearance 

 and multiply rapidly. 



The signification, however, that must be attached to these 

 different evolutions is still somewhat ambiguous, since plainly 

 tropical types, such as the Pandanese, are thenceforward asso- 

 ciated with subtropical Australian types, such as the Proteaceae 

 and Araucaria, boreal types, such as Sequoia and Cedrus, or 

 cosmopolite types, such as the Myricese. All these indications 

 combined seem to denote a tropical temperature with no excess, 

 probably variable according to the seasons in a degree which it 

 is difficult to appreciate. 



The inferior Tertiary, including the Tongrian, forms a new 

 period, during which the genera which have since continued 

 characteristic of the boreal zone appear in juxtaposition with 

 genera with tropical or subtropical affinities; but the former 

 remain stationary or subordinate, whilst the latter do not cease 

 to develope themselves and maintain their preponderance. Ac- 

 cording to all indications, the temperature was then that of the 

 present tropical -regions; but the climate (that is to say, the 

 proportion of humidity and the distribution and economy of the 

 seasons) must have varied several times — changes reflected by the 

 vegetation, which differs from stage to stage, whilst that of each 

 stage presents a general resemblance. It is by this means that 

 we may explain the alternate predominance and exclusion of the 

 Proteaceae, and the successive enlargement and diminution of 

 the leaf, through the Suessonian, Eocene, and Tongrian stages. 



The Miocene, or Middle Tertiary, constitutes by itself a fifth 

 period, during which the vegetation of ancient Europe attains its 

 highest degree of development. This state of things is prolonged 

 up to the level of (Eningen, but without remaining stationary : 

 the types characteristic of our zone are constantly being deve- 

 loped and completed, as well as the subtropical types ; the tro- 

 pical and Australian types, on the contrary, tend to depart and 

 disappear. 



The Pliocene age constitutes a last period, during which the 



