549 TEE SCIENTIFIC MONTHLY 



the Bulletin of the Torrey Botanical Club there appeared in an ac- 

 count of the floral regions of that area, the statement that 



Any rational catalogue of our flora should distinguish what plants are 

 absent from or peculiar to each natural region and should contain such infor- 

 mation in reference to soil, climate, etc., as may help to elucidate the dis- 

 tribution. 



Among purely local botanists, this was, I think, the first statement 

 implying causation that had appeared. Gray, Torrey and Hooker had 

 all written extensively of the flora of North America, and some of 

 them, at any rate, had written on the larger problems of the origin 

 and distribution of the North American flora. For the region about 

 New York, with its variety of conditions, there seems to have been no 

 opportunity until quite recently to attempt to fulfil the hope of the 

 writer in 1870 who is quoted above. 



Eecent studies of the fiora show that there are about 2,600 different 

 species of flowering plants and ferns known to grow within, roughly, 

 100 miles of the City. Of these 85 are ferns and their allies, 23 are 

 conifers and the balance is made up of our ordinary flowering plants. 

 Of the total flora some 613 species have been introduced from outside 

 the area, by man or otherwise, leaving slightly more than 2,000 species 

 of native plants in the region within one hundred miles of the City.^ 



It is a matter of common observation that these plants are not 

 generally distributed throughout the region. In traveling from the 

 Catskills to Cape May, the northern and southern limits of the area 

 studied, we see a variety of plants found in one or the other of these 

 widely separated localities, but not in both of them. Many species find 

 their outposts of distribution near New York. Some appear to have 

 come from the North or South, a few from the West, others are appar- 

 ently endemic in the area, and this great quantity of forms, the ap- 

 parent chaos of it all, raises many questions. What is the real com- 

 position of our flora, whence derived, and above all how did it reach its 

 present luxuriance and beauty? The attempt to answer these ques- 

 tions necessitates a review of the causes that have influenced the origin 

 and distribution of our native flora. 



For all practical purposes the agencies affecting the distribution of 

 our native plants may be divided into edaphic and climatic ones. 

 Under the first must be considered all questions of the relation of the 

 vegetation to the soil and available water supply ; or more simply stated 

 the geological factors of distribution; under the second the relation 

 of the flora to climate must be the chief concern. 



From the point of view of plant distribution the last geological 

 phenomenon is the most important, as the continental glacier the fringe 

 of which stretched through Long Island, Staten Island, northern New 

 Jersey and Pennsylvania, had a profound influence on the migration 



1 Mem. N. Y. Botanical Garden, 5, 1-683, 1915. 



