OF WESTERN PENNSYLVANIA. 23 



Order I. SPHAGNALES. Peat Mosses. 



Characteristic peat mosses, in bogs, usually either in water 

 or water-soaked, monoicous or dioicous, deeply cespitose, the 

 tufts constantly growing upwards at the same time that the 

 plants are dying from below and often thus giving rise to deep 

 beds of peat, the tufts light grayish-green or sometimes yel- 

 lowish, often more or less tinted with red above : stems with- 

 out rhizoids, usually composed of an outer cuticular sheath 

 consisting of one to three or four layers of large lax cells, an 

 intermediate wood cylinder composed of prosenchymatous 

 cells with usually thickened walls, and a central pith of lax 

 parenchymatous cells ; branches symmetrically fascicled, 

 usually partly divergently spreading and partly slender and 

 appressed-pendent ; leaves ecostate, unistratose, composed of 

 large, hyaline, more or less elliptic cells with usually per- 

 forated and spirally thickened (fibrillose) walls and separated 

 by narrow chlorophyllose cells which meet at their ends to 

 form a continuous network throughout the leaf; stem-leaves 

 usually different in form from the branch-leaves, remote, often 

 lacking entirely the pores and spiral fibrils, while the branch- 

 leaves are usually porose, fibrillose, and more or less densely 

 imbricated ; seta none but the capsule is borne upon an out- 

 growth from the gametophyte termed a pseudopodium ; an- 

 theridial flowers usually at the apex of specialized branches 

 of the capitulum, the antheridia being pedicillate, globose, and 

 solitary at the base of the bracts; the archegonial flowers 

 gemmiform, axillary in one of the upper fascicles, only one 

 of the three or four archegonia developing, as a rule : capsule 

 globose, castaneous, with a convex operculum, without annulus 

 or peristome; calyptra irregularly lacerate; spores developed 

 from the amphithecium, the columella from the endothecium. 



This order is a peculiar one comprising but one family 

 (Sphagnaceae) which contains but the one genus {Sphagnum) 

 with about 250 known species. The Sphagnums are cos- 

 mopolitan in suitable habitats but are most abundant in the 

 cooler temperate regions of Europe and North America, in 

 both of these countries often forming bogs of large areas. In 

 North America there are known about 75 species, at least 20' 

 of these occurring in our range. 



I. SPHAGNUM [Dillenius] Hedwig. 



Analytical Key to the Species. 



a. Cuticular cells of the stem and usually also of the divergent 

 branches porose and spirally fibrose; branch-leaves with a hyaline 

 entire border, concave, cucuUate, obtuse but hardly truncate. 



b (Cymbifolia). 



a. Cuticular cells of the stem and divergent branches not porose nor 



