FROM AN OLD STANDPOINT. 



193 



present time tlie greater is the similarity between tlie widely 

 removed and now dissimilar floras of Xorth America, Europe, 

 nnd Australia. (I have here quoted Mr. Eeid's article on 

 Tertiary floras in volume 31 of the Eiieyclopccclict Britannica.) 



The extension of tropical plant-forms far north into the 

 temperate latitudes during early Tertiary times is well known, 

 ■and Saporta long since placed the northern limit of tropical 

 vegetation in the Eocene age at 55° X. These plants retreated 

 towards the equator as the development of climatic zones 

 proceeded, and many of them yet exist in a generic sense 

 within the tropics. Temperate genera like Acer, that flourished 

 in early Tertiary times in Arctic latitudes, followed in the 

 rear of the tropical genera in their withdrawal towards the 

 south. The shifting area of this genus in geological time is 

 •clearly elucidated by Pax in his recent monograph on the 

 AceraceaB {Das Pflanzoireich, iv, 163). Speaking generally, 

 during the earlier and middle Tertiary times this genus 

 <3xtended in the northern hemisphere from far within the 

 Arctic Circle to the 40th parallel of latitude, and perhaps 

 farther south. As the ages passed away it abandoned the 

 Arctic latitudes and advanced to within tiie tropics, so that its 

 xiverage range at the present time is confined between the 

 parallels of 20° and 00° N., although individual sections have 

 indeed penetrated farther south into Malaya, reaching Sumatra 

 iind Java. Of the earlier history of Acer we apparently know 

 ])ut little ; but the facts, scanty as they are, are very suggestive. 

 Among the fruits found by Mr. ]S'ewberry* in tlie Amboy 

 €lays of New Jersey, the equivalent of the White Chalk of 

 England, were those of a species of Acer " quite unmis- 

 takable " in character. They were associated in this locality, 

 which is situated near the 40th parallel, not only with the 

 remains of several genera, such as Populus and Quercus, that 

 ^ire now mostly confined to temperate latitudes, but with many 

 •others, such as Cinnamonum, Ficus and Myrsine, that are now 

 mainly restricted to tropical regions. The pre-Tertiary history 

 of Acer would thus seem to belong to an age when the 

 distinction between tropical and temperate floras had not been 

 •established. 



It is the occurrence of these " mixed " angiospermous floras 

 •during Cretaceous and Eocene times in extra-tropical regions 



* U.S. Geolog. Survey, Flora, of tlie Amho}/ Clays, by J. S. Newberry, 

 i895. 



