OF WESTERN' PENNSYLVANIA 127 



Characters as for the family. 



The Ohio station for this species is only a few miles from 

 the northwestern corner of Pennsylvania and the species may 

 eventually he discovered in our region. 



Family XL EPHEMERACEAE. 



Autoicous or dioicous, rarely polyoicous or synoicous : 

 minute, about 1-2 mm. high, singly disposed or gregarious, 

 mostly stemless ; protonema sometimes persistent ; leaves min- 

 ute, linear to lanceolate or ovate to obovate, often tufted, 

 rosette-like, spreading or erect-spreading ; leaf-cells mostly lax, 

 more or less elongate below, rectangular to rhomboid-hexa- 

 gonal, above shorter, usually smooth ; costa none to excurrent, 

 usually present: seta none or short; capsule immersed, sub- 

 globose, cleistocarpous ; operculum sometimes differentiated 

 but rarely deciduous of itself ; spores mostly large and papil- 

 lose : calyptra mostly small, delicate, mitrate-campanulate. 



Minute plants growing on soil. 



Key to t/ie Genera. 



a. T. caves lanceolate: green protonema persistent. 



i. Hphemerum* 

 a. Leaves ovate: green protonema not persistent. 



b. 



1). Stem none. 2. Acaulon. 



b. Stem evident. .3. Physcomitrella. 



1. EPHEMERl'M Hampe. 



Dioicous, rarely polyoicous : minute plants with abundant 

 and persistent green protonema : upper leaves elongate-lanceo- 

 late to linear ; costa none or variously developed ; leaf-cells 

 lax, mostly thin- walled, rhomboidal : seta rudimentary or none; 

 capsule mostly globose and apiculate, cleistocarpous, walls of 

 one layer of cells with stomata ; spores large, up to .08 mm. in 

 diameter, warty ; calyptra campanulate, delicate, torn at the 

 base or sometimes only on one side. 



A cosmopolitan genus of about 25 species ; 8 or 9 species 

 occurring in North America, perhaps most of these occurring 

 in our region, but on account of their minute size not yet col- 

 lected. 



Key to the Species. 



^. Costa none. b. 



a. Costa more or less complete, or vanishing towards the base. 



c. 

 b. Leaves lanceolate, erect-patent, spores .060 .080 mm. 



(. serratum [Schreber] 



Hampe.) 



*Xan<>initrinni Lindberg (Micromitrium Austin) differs from Epheui- 

 cntin in having a rudimentary but not deciduous operculum and the 

 capsule without stomata and with a wall but one cell thick. 



