OF WESTERN PENNSYLVANIA 281 



about the middle of the leaf, sometimes strong and percurrent 

 or even excurrent ; leaf-cells mostly long-linear, smooth, in the 

 more or less excavate angles parenchymatous, thin-walled and 

 hyaline or thick-walled and colored, usually forming a well- 

 defined group sometimes reaching to the costa; inner peri- 

 ch^etial erect, mostly plicate, elongate-subulate : seta long to 

 very long ; capsule inclined to horizontal, cylindric, arcuate, 

 when dry constricted below the mouth, smooth, annulate; lid 

 convex, apiculate. 



A genus of over 40 species of water-mosses, quite largely 

 swamp-mosses, often forming quite large masses of vegeta- 

 tion. almost exclusively confined to temperate and cold re- 

 gions; about 22 species occur in Xorth America, perhaps the 

 following four to be included in our list. 



Key to the Speeies. 



a. Stem in cross-section displaying cortical layer of enlarged hyaline 



cells. 1. D. uucinatus. 



a Stem without such a layer. b. 



b. Leaves usually entire, the ends of stems and brandies not or 



but slightly hooked. 2. D. knciffii. 



b. Leaves serrulate, ends of stems and branches hooked. 



c. 



c. Costa usually less than three-fourths length of leaf: alar group of 

 cells not reaching over to the costa. 



3. D. fluitans. 



c Costa extending well up to the apex of leaf: alar group of cells 

 large, excavate, and extending over to the costa. 



4. D. e.vannulatus. 



1. Drepanocladus uncinatus [Hedwig] Wamstorf. 



(Hypnum uncinatum Hedwig; Amblystegium aditncuui Lind- 

 berg; Hypnum aduncuin Linnaeus). 



Rather slender and loosely interlaced, pale green or golden 

 green : stems distantly and irregularly pinnately branched, 2-10 

 cm. long, in cross-section showing a layer of large hyaline 

 cortical cells ; leaves rather crowded, regularly falcate to sub- 

 circinate, little altered when dry, spirally flexuose at the points 

 in the younger and softer branches, narrowly elongate-lanceo- 

 late, strongly plicate both wet and dry, gradually very long 

 and slenderly acuminate, usually denticulate above, texture 

 very thin ; costa narrow, about .030-.035 mm. at base, extending 

 well into the acumen ; leaf-cells very long, linear-flexuous, thin- 

 walled, pointed, uniform to the base and apex, the alar forming 

 a rather small and indistinct group of slightly enlarged and 

 slightly inflated cells, and extending decurrently below and 

 marginally a short distance above; perichaetial leaves erect, 

 straight, long, plicate, sheathing: seta variable, but usually 

 2-3 cm. high ; capsule cylindric, arcuate, orange-red, darker 

 when old. when dry and empty somewhat constricted below 



