432 MIOCENE PLANTS AND INSECTS CHAP. xxn. 



homologous forms, which are so like the living ones, that he 

 supposes the one to have been derived genealogically from 

 the others. He hesitates indeed as to the ' manner of the 

 transformation, or the precise nature of the relationship, 

 " whether the changes were brought about by some influence 

 exerted continually for ages, or whether at some given 

 moment the old types were struck with a new image." 



Among the homologous plants alluded to are forty species, 

 of which both the leaves and fruits are preserved, and thirty 

 others, known at present by their leaves only. In the first 

 list we find many American types, such as the tulip tree, 

 Liriodendron, the deciduous cypress, Taxodium, the red 

 maple, and others, together with Japanese forms, such as the 

 cinnamon, which is very abundant. And what is worthy of 

 notice, some of these fossils so closely allied to living plants 

 occur not only in the Upper, but even some few of them as 

 far back in time as the Lower Miocene formations of Switzer 

 land and Germany, which are probably as distant from the 

 Upper Miocene or Oeninghen beds as are the latter from our 

 own era. 



Some of the fossil plants to which Professor Heer has 

 given new names have been regarded as recent species by 

 other eminent naturalists. Thus, Unger had called one of 

 the trees allied to the elm, Planera Richardi, a species 

 which now flourishes in the United States. Professor Heer 

 had attempted to distinguish it from the living tree by the 

 greater size of its fruit, but this character he confessed did 

 not hold good, when he had an opportunity (1861) of com 

 paring all the varieties of the living Planera Richardi 

 which Dr. Hooker laid before him in the rich herbarium 

 of Kew. 



As to the ( homologous insects' of the Upper Miocene 

 period in Switzerland, we find among them, mingled with 

 genera and orders now wholly foreign to Europe, some very 



