2 INTRODUCTION 



notes. The keys and general ranges have been copied from "Illus- 

 trated Flora," except where simplicity demanded a different key 

 owing to the limited number of species in our area. There are 

 2,651 species admitted into the work, excluding waifs. Subtract- 

 ing also the 613 weeds of introduction we have 2,038 native species 

 in the area. No species are described as new. 



3. With this information as a basis, the distributional trends 

 of each species, except the commonest or those introduced, 

 have been given for the states of Connecticut and New Jersey, 

 and for those parts of the states of New York and Pennsylvania 

 contained in the range. Wherever a state or part of it is omitted 

 from the discussion of the distribution, it is understood that the 

 species has not been recorded from the omitted area. Besides 

 this, the distribution of each species as affected by the geological 

 history, the temperature, and the altitudinal limits of the area 

 has been given. The latter features of the work will be explained 

 subsequently. 



FACTORS AFFECTING THE DISTRIBUTION OF OUR LOCAL FLORA 



4. The composition of the flora of a region such as ours has 

 been determined by many agencies, some now operative, many 

 of them long since inactive, but leaving indelible traces of their 

 former importance. For all practical purposes, these agencies 

 may be divided into (I) edaphic factors and (II) climatic ones. 

 Under the first category must be considered all questions of the 

 relation of our flora to the soil and available water supply, both 

 past and present, — which ipso facto have been determined by the 

 geological history of the region. Thus it is only by some knowl- 

 edge of the geology of the area that we can arrive at conclusions of 

 value in regard to the complexion of our flora as affected by these 

 historical factors. Under the second category (climatic factors) 

 will be considered the relation of our flora to temperature, rainfall 

 and winds, although in a temperate region such as ours the last 

 two are of very little significance. We have, then, the edaphic or 

 historical factors, which may be said to have exercised more in- 

 fluence in the past than now, and the climatic factors which 

 are still operative. The mental convenience of considering these 

 two sets of factors by themselves is apt to create the feeling that 

 there is some rather sharp line of demarcation between them. Of 



