322 A MANUAL OF MOSSES 



A genus of about 35 species, mostly growing on rocks and 

 stones, rare in the tropics; about 17 species in North America; 

 at least 4 species in our region. 



Key to the Species. 

 a. Leaves spreading more or less uniformly in all directions. 



b. 

 a. Branches distinctly complanately flattened. 



c. 

 b. Leaves entire. 2. P. roeseanum. 



b. Leaves more or less, serrulate. L P. striateUum. 



c. Costa strong, forked, often reaching to the middle of the leaf: 



capsule usually striate when dry. 3. P. sylvaficum. 



c. Costa thin, short: capsule usually smooth when dry. 



4. P. denticulatum. 



1. Plagiothecium striatellum (Bridel) Lindberg. 

 (Hypnuin muehlenbeckii Schimper; Plagiothecium mnchlenbeckii 



Bryologia Europsea; Leskea striatella Bridel). 

 (Plate XLVII) 



Slender, dense, dark green, lustrous: stems prostrate, 

 branches crowded, erect or ascending, straight or slightly 

 curved; leaves about 1-1.3 mm. long, crowded, sub-com- 

 planate, the branch-leaves squarrose-spreading, ovate-lanceo- 

 late or triangular-lanceolate with a long slender and flexuous 

 acumen, plane-margined, serrulate above at least, the base 

 strongly decurrent ; CQSta double and faint ; median leaf-cells 

 linear-fusiform, flexuous, rather short, about 6-10:1, the basal 

 somewhat larger, the alar abruptly very much enlarged, in- 

 flated, hyaline to colored, and forming the much decurrent 

 and plainly distinct auricles ; inner perichastial leaves half- 

 sheathing, the apex filiform-flexuous and usually recurved : 

 yellowish, about 2 mm. long, slightly curved, oblong-cylindric 

 with a tapering neck, distinctly striate when dry; lid conic, 

 rather obtuse; annulus large, compound; exothecial cells 

 minute and rounded in three to five series at the rim, below 

 rapidly becoming irregularly oblong and more or less in- 

 crassate ; teeth short, yellowish, papillose above, dorsally cross- 

 striolate below, lamellate, strongly trabeculate, slightly con- 

 fluent at base; segments about as long, slender, pale, granu- 

 lose, only slightly carinately cleft ; basal membrane only about 

 one-fourth to one-third as high as the teeth ; the cilia 1 to 3, 

 a little shorter than the segments ; spores mature in late spring 

 or early summer, yellowish, papillose, rather incrassate, 

 .007-.010 mm. 



On earth, rocks, and rotten logs, in woods, usually in non- 

 calcareous habitats; Europe, and from Arctic America south 

 to North Carolina. Rare in our region. 



Cambria : Ebensburg. T. P. James. (Porter's Cata- 



logue). 



