by Deciduous Plants in the Tertiary Floras. 295; 



leaves, and the other to that of flowers. It is thus that we 

 must conceive the position of the deciduous plants at an epoch 

 when the seasons were far from being regulated as they are at 

 present. Their existence only apparently contrasts with that 

 of the exotic plants with which they are associated ; this dis- 

 parity is effaced when we take into account^ as we have just tried 

 to do, what are these vegetable forms considered in themselves, 

 abstracted from the changes to which they subsequently yielded 

 more readily than the others. Their subsequent development 

 and actual preponderance lead us to exaggerate their original 

 importance, which in reality was very small. If afterwards it 

 was otherwise — if the changes of temperature brought about by 

 the lapse of time have contributed to increase the importance of 

 these plants, this result (the effect of causes which were not yet 

 in action at the epoch when we see them for the first time) must 

 not lead us into error as to what they originally were. It is this 

 first stage that we propose to analyze ; and its knowledge will 

 allow us to appreciate more justly the circumstances which sub- 

 sequently brought about their multiplication correlatively with 

 the exclusion of the forms which had previously predominated. 



The frutescent plants with deciduous leaves and a European 

 physiognomy, in the flora of the gypsum of Aix, amount to 15 

 at most, out of 118 dicotyledons. If from this number we 

 deduct the more doubtful forms (those which present some 

 analogy with living forms with persistent leaves, and those of 

 which the leaves are still unknown), the number is reduced to 

 8 species only, that is to say, the insignificant proportion of 

 Q'77 per cent. These species are the following : — 



Betula gypsicola, Sap. Acer ampelophyllum, Sap. 



Ulmus plurinervia, TJng. Paliurus tenuifolius, Heer. 



Populus Heerii, Sap. Crataegus nobilis, Sap. 



Ribes Celtorum, Sap. Cercis antiqua, Sap. 



Nearly all these species belong to genera in which the flowers 

 are often developed in the absence of the leaves, as in most of 

 the Betulacece, Ulmus, many species of Populus, Acer, Ribes, 

 Cercis, &c. It is probable that this was the case with the Ter- 

 tiary species, and that their flowering coincided with the cool 

 season, or that which took the place of winter, and during a 

 portion of which these plants remained denuded of leaves as at 

 present. 



The most abundant of all these trees is the Cercis antiqua ; 

 all the others are excessively rare, or even unique. The Cercis, 

 notwithstanding its identity with a genus now represented in 

 Southern Europe, North America, and Japan, is not a charac- 

 teristic type of the boreal zone. The living species of this genus 



