INTRODUCTION. 



SOUTHERN SPECIES. So far as we are able to learn the following 

 southern and southwestern species extend no farther north or northwest 

 (or but little farther), although a few extend along the coast into New 

 York or New England : 



Arabis dentata, Betzda nigra, 



Dicentra eximia, Pinus inops, 



Silene Pennsylvania, Aletris farinosa. 



Ilex mollis, Melanthium latifolitim, 



Robinia Pseudacacia, Amianthium musca:toxicum, 



Helianthus parviflorus, Scleria paziciflora, 



Rhododendron canescens, Panicum agrostoides, 



Cunila Mariana, Triodia cuprea. 



The above divide themselves into two groups, the plants belonging to 

 the valley and the plants belonging to the dry ridges of the mountains, 

 corroborating the evidence we find from actual observation, of their ori- 

 gin in a warmer region. We trace the beautiful River Birch up the 

 branches of the Delaware, up the Susquehanna from its mouth to above 

 the Wyoming Valley, but not certainly beyond Tunkhannock, and up 

 the Lackawanna to Peckville. Like the dusky Pinus inops, its presence 

 suggests the peculiar warmth of the south. Robinia was noticed more 

 than a century ago by travellers crossing "Locust Ridge" on the Pocono. 

 This, with Melanthium and Amianthium, two curious Liliacerc, are 

 characteristic of the mountain group of the southern species. 



NORTHERN SPECIES. But our Flora is -connected with the north by a 

 far greater number of peculiar species than with any other region. Above 

 fifty-five northern species have been found which do not extend south 

 of our territory. This number, moreover, does not include those species 

 recognized as northern, but which extend through this section, along the 

 Alleghenies to North Carolina or Georgia. Twenty of the fifty-five 

 belong to the Heaths and the Sedges. The Rhodora, the Pale Laurel, 

 the Labrador Tea, the Small Cranberry, the Cotton Sedge, all particu- 

 larly attractive plants, belong to these two orders. Nearly all these 

 northern forms are confined to the mountains, and in the case of 

 those found in the valley, as well such as Portentilla palustris, I sus- 

 pect they will ultimately be discovered much further south, where they 

 have retreated wholly to the mountains. 



WESTERN SPECIES. Turning to the west, I have been able to find 

 but two western species extending eastward only to our limils, a garlic, 

 Allium ccrnuum, and a grass, Kccleria cristata. 



