NATURAL SCIENCES OF PHILADELPHIA. 



11 



leaves in the autumn much longer than closely allied American species grow- 

 ing near them, and that this could not be owing to immediate climatic influ- 

 ences, as Gleditschia triacanthos, Robinia pseudacacia, and other American 

 trees, with no European representatives, possessed the same characters, I was 

 led to believe it was rather the result of inherent specific peculiarities, which 

 further investigation tended to confirm. 



It will be seen from the subjoined table that on any positive difference 

 being ascertained to exist between an American and a closely allied European 

 species, the relative differences between all other closely allied species of the 

 same differing geographical distribution are of the same character and nature. 



For instance, the European Plane (Platanus orientalis) maybe distinguished 

 by a compactness of growth when compared with the diffuse habit of the 

 American species, and the same compactness and diffuseness will be found to 

 prevail in all the respective European and American species of other genera. 



The nut of the European chestnut {Castanea vesca) is characterized by large 

 size ; the American ( C. Americana) is much smaller, and the seeds of all 

 allied European and American species bear the same relative proportions ; and 

 so of other characters that I have compared, and which I may enumerate as 

 follows : 



1st. Color and persistency of the leaves. In which the American species 

 change to some brilliant hue, and fall comparatively early, while the European 

 co-species fade black, and are retained to a later period of the season. 



2d. Outline of the leaves. In which the American species have the leaves 

 less lobed, less deeply toothed or serrated, less in width in proportion to their 

 length, and less petiolate than the European species. 



3d. Size of the seeds. In which the American are smaller than the European. 



4th. Habit of growth. In which the American is more diffuse, has much 

 fewer branchlets, and more and more vigorous main branches, and the outline 

 more irregular and informal than European trees. 



5th. Size of the buds. In which the American have smaller ones than the 

 European, and usually set at wider spaces between the nodes. 



The observations finally made were taken at Germantown, Pa., during the 

 first week in November, 1861. 



European Species. 

 Laiix Europaea. 

 Quereus robur. 



" cerris. 

 Betula alba. 

 Populus tremula. 



" dilatata. 

 Morus alba. 

 Euonymus Europaeus. 

 Spiraea salicifolia. 

 Berberis vulgaris. 

 Carpinus betulus. 

 Cornus sanguinea. 

 Ulmus campestris. 

 Corylus avellana. 

 Alnus glutinosa. 

 Castanea vesca. 

 Pyrus malus. 

 Tilia Europaea. 

 Ulmus montana. 

 Fraxinus excelsior. 

 Cerasus padus. 



" mahaleb. 

 Fagus sylvatica. 

 1862.] 



American species. 



Larix Americana. 



Quereus alba. 



" macrocarpa. 



Betula populifolia. 



Populus grandidentata. 

 " Caroliniana. 



Morus rubra. 



Euonymus atropurpureus. 



Spiraea carpinifolia. 



Berberis Canadensis. 



Carpinus Americanus. 



Cornus sericea. 



Ulmus Americana. 



Corylus Americana. 

 Alnus serrulata. 

 Castanea Americana. 

 Pyrus coronaria. 

 Tilia Americana. 

 Ulmus fulva. 

 Fraxinus acuminata. 

 Cerasus Virginiana. 



" serotina. 

 Fagus ferruginea. 



