166 American Midland Naturalist Monograph No. 6 



3. PoLYTRiCHUM Dillenius, Hedwig 

 Hair-Cap Moss 



Dioicous; antheridial flowers cup-shaped, sprouting from the middle: 

 robust, stiff, in green to bluish-green, mostly high tufts; stem with a complete 

 central strand, rising from a subterranean rhizome, often whitish tomentose, 

 mostly simple; leaves dense, erect spreading to recurved, drying stiffly erect, 

 from a sheathing scarious base elongate-lanceolate to linear-subulate, non-bor- 

 dered, with margin plane to involute, sharply serrate, the sheathing base uni- 

 stratose and hyaline, at least at the angles; lamina bi-stratose except at the 

 margin; costa narrow and flat below, above stronger, dorsally toothed towards 

 apex, mostly excurrent as a colored, toothed awn; lamellae erect, high, numer- 

 ous, covering the costa and the bi-stratose lamina ventrally; cells in the sheath- 

 ing base elongate-rectangular to linear, narrower marginward; laminal cells 

 small, incrassate, quadrate-hexgonal : sporogonia solitary; seta long, stiff yellow- 

 ish-red to purplish, often drying flat and sinistrorse; capsule first erect, finally 

 inclined or horizontal, mostly prismatic, 4-6-angled, oblong to cubic, collum 

 hemispheric or disk-like, with stomata; spore-sac free; teeth 64, with a colored 

 axis, basal membrane colored; operculum large, conic to convex, rostrate; 

 calyptra cucullate and with the long, shaggy hairs completely enclosing the 

 capsule. 



About 100 species, ma-'nly on soil in the cooler parts of the globe; about 

 20 species in North America; at least 5 species in our range. 



Key to the Species 



A. Exothecial cells of the capsule not pitted B 



B. Exothecial cells of the capsule pitted C 



B. Marginal cells of the lamellae like the others in size and cell-walls 1. P. gracile 



B. Marginal cells of the lamellae thicker walled and in cross-section obversely pyri- 



form 2. P. ohioense 



C. Leaf-margin entire, broad and infle.xed; marginal cells of lamellae not emarginate in 



cross section D 



c. Leaf-margin sharply serrulate, not inflexed; marginal cells of lamellae emarginate in 



cross-section 6. P. commune 



D. Excurrent costa long, hyaline; plants low (about L5-2 cm tall), simple 



- 3. P. piliferum 



D. Excurrent costa red, short; plants larger E 



E. Stems not or but slightly tomentose; capsules oblong-tetragonal 4. P. juniperinum 



E. Stems whitish-tomentose below; capsules more or less cubical 5. P. alpcstre 



1. POLYTRICHUM GRACILE Dickscn 



Plate LXXII 



Tufted, dark green, erect; stems 3-10 cm tall, matted together below with 

 brownish tomentum; leaves erect-spreading when moist, somewhat curled and 

 twisted when dry, the upper ones longer, 7-10 mm long, the lower one- fourth 

 to one-third portion of the leaf oblong, about 1.5 mm wide, abruptly tapering 

 upwards into a long, very slenderly acuminate, serrulate-spinose tip, the basal 

 sheathing portion of the leaf with thin rectangular cells .035-.070 mm long, 

 one-half to one-third as wide, with narrower cells in a few marginal rows, the 



