VI PEEFACE. 



The list referred to above forms the basis of the present flora. 

 Numerous additional species have been collected in the county by the 

 authors of this volume and by their many associates and correspondents. 

 Specimens of these species have been widely distributed, but the more 

 complete sets occur in the herbarium of the New York Botanical Garden, 

 the herbarium of Franklin and Marshall College, the herbarium of J. J. 

 Carter, the herbarium of the Field Museum of Natural History, the her- 

 barium of A. A. Heller, and the herbarium of the Academy of Natural 

 Sciences of Philadelphia. All records of species on the following pages 

 axe based on specimens collected in the county. 



Lancaster County comprises almost 1000 square miles. Its extreme 

 width, east and west is 47 miles, its extreme length, north and south, 41 

 miles. It lies southeast of the Appalachian Mountain System. There are 

 no considerable altitudes attained by its hills, but the surface is quite 

 diversified. Rolling hills and winding streams are numerous. The latter 

 flow, without exception, either directly or indirectly into the Susquehanna 

 River. The Susquehanna runs along the western boundary of the county 

 for a distance of more than 40 miles, and for over half of this distance it 

 passes through a most picturesque canon with steep sides and wild lateral 

 branches. This canon has a southern exposure, and plants of a typically 

 more southern flora have here made themselves at home. On the other 

 hand, plants of a typically more northei'n flora are found in the cool 

 siDhagnum swamps among the hills of both the northern and the southern 

 parts of the county. These two somewhat extraneous elements, together 

 with the plants typical of the greater part of our area and the contiguous 

 teiTitory, comprise a flora of more than ordinary interest and diversity. 



The county is divided by its main geological formations into three 

 topographical or geographical belts or zones. They are: (1) a northern 

 belt of sandstones and shales, (2) a middle belt of limestones, and (3) a 

 southern belt of schists. On the one hand, all three belts contain trap-dikes 

 or outcrops of trap rock. On the other, the sandstones and shales are 

 uninterrupted, except for a bay of limestone prolonged northward from the 

 middle belt; the uniformity of the limestones is broken mainly by several 

 small outcrops of quartzite, while the schists contain some small projections 

 of limestone at the northern edge and several outcrops of serpentine at the 

 southern end. 



On the following pages when a species is confined to one or several 

 parts of the county the fact is indicated by N. (northern), M. (middle), 

 S. (southern), W. (western), E. (eastern). Likewise, when a species is 

 confined to one or two geological fonnations or is characteristic of such, 

 the fact is so indicated. When a species is generally distributed only its 

 habitat is mentioned. Other abbreviations used are Spr. (spring). Sum. 

 (summer), Eu. (Europe), As. (Asia), Nat. (native). 



