136 OUR NATIVE FERNS AND THEIR ALLIES. 



two to many ranks on trailing or sometimes erect, usually 

 branching stems. Sporangia i 3 celled, solitary in the axils 

 or the leaves, or on their upper surface. Spores of one kind, 

 minute. Prothallia (so far as known) mostly subterranean, 

 with or without chlorophyll, monoecious. Contains four gen- 

 era, the following within our limits: 



I. Lycopodium L. Leaves well developed, in 4 many 

 ranks. Sporangia i-celled. 



II. Psilotum R. Br. Leaves minute, abortive. Sporangia 

 3-celled. 



I. LYCOPODIUM L. CLUB-MOSS. 



Perennial, terrestrial plants, with evergreen, one-nerved 

 leaves arranged in 4 16 ranks. Sporangia coriaceous, flattened, 

 reniform, one-celled, opening transversely, situated in the axils 

 of ordinary leaves, or with fruit-bearing leaves modified into 

 bracts which are arranged in spikes either sessile or peduncled. 

 Spores copious, minute, sulphur-colored, inflammable. Named 

 from Gr. hvxoS, wolf, and TCOV$, foot, without obvious applica- 

 tion. Contains nearly one hundred species. 



i. PLANANTHUS Beauv. Sporangia borne in the axils of 

 leaves which are similar to those of the sterile and fertile stems. 



* Sporangia usually wanting in axils of upper leaves ; leaves 

 dark-green, shining, about %-ranked. 



1. L. selago L. Stems 3' 6' high, thick, rigid, erect, 2 

 3 times forked, forming a level-topped cluster; leaves elon- 

 gate-lanceolate, mucronulate, entire or spinulose-denticulate, 

 nerved above, convex below. (L. recurvum Kit., L. suberectum 

 Lowe, Plananthus selago Beauv.) Mountains of North Caro- 

 lina to New England and Michigan, and northward to Alaska 

 and Greenland. 



2. L. lucidulum Michx. Stems ascending, thick, 2 3 

 times forked, the branches 6' 12' high; leaves widely spread- 

 ing or reflexed, flat, one-nerved, acute, minutely toothed. (L. 

 refle.xum Swz., L. serratum Desv., Plananthus reflexus Beauv.) 

 North Carolina and northward. 



** Sporangia only in axils of upper leaves which form spikes; 

 leaves many-ranked. 



3. L. inundatum L. Sterile stems creeping, flaccid, fork- 



