Jennings: Manual of Mosses 5 



the valleys often rapidly narrow to a more or less steep rock-walled canon 

 where erosion is highly active. In the narrow valleys the forest covering has 

 not been very extensively disturbed by man and the damp, cool, shaded 

 habitat with varying substrata of decaying wood, rich loam, shaly soil, bare 

 rock, or living bark, conduces to a rich and varied flora of the Bryales. Above 

 this area of active erosion there will usually be found, in the headwaters of the 

 streams, a region which has remained largely unaltered from a former ad- 

 vanced stage of physiographic development and which is characterized by wide 

 valleys with gently sloping soil-covered sides rising to broadly rounded and 

 soil-covered hills. These rounded hills, whose height above the bottoms of 

 the adjacent rounded valleys is rarely more than 300 to 350 feet, are in many 

 places still covered with the native forest consisting mostly of the white oak, 

 but the moss flora of these forests is poor. 



Good collecting ground for the Bryales is also to be found in the moun- 

 tams of the eastern and southeastern parts of the region covered by this 

 Manual, particularly in the steep and rocky gorges which have been cut 

 through the sandstone ridges by the larger streams. Perhaps the best collect- 

 ing ground for the Bryales in our whole region is to be found in the vicinity 

 of Ohio Pyle, in Fayette County, where the Youghiogheny River and its 

 larger tributaries have cut out wild and rocky gorges sometimes a thousand 

 feet or more in depth. Somewhat similar and perhaps but little inferior to 

 the Ohio Pyle region are localities along the gaps cut through the ridges by the 

 Conemaugh and Loyalhanna rivers and the eastward-flowing Juniata and the 

 West Branch of the Susquehanna River. 



The northeastern part of our region consists of an elevated plateau in part 

 still swampy or boggy but in part considerably dissected. The flora is largely 

 of a northern type, much of it having been originally of the northern mixed 

 hardwood forest of hemlock, birch, beech, and maple, but with areas more or 

 less dominated by white pine. This plateau region is a rich moss collecting 

 ground both for the Bryales and the Sphagnums. 



In the present edition much the same sequence of families has been ob- 

 served as in the first edition. In classifying mosses, both gametophyte and 

 sporophyte characters are of value, and it is practically impossible to arrange 

 them in a satisfactory sequence. An arrangement based on either gametophyte 

 or sporophyte characters will cut across the other, and current practice varies 

 considerably. The old practice of grouping the mosses into acrocarpous, with 

 the sporophyte borne terminally on either the stem or evident branches, or 

 pleurocarpous, with the sporophyte borne laterally, is not accurate, but it is 

 very convenient for purposes of identification, particularly since it is desir- 

 able to identify so many specimens in which the sporophytes are not in proper 

 condition to study. As a matter of convenience these two groups are recog- 

 nized in the present work. 



The following twenty- six species have now been definitely added to the 

 known moss-flora of western Pennsylvania since 1912 and are also described 

 and illustrated in this second edition. 



