PTERIDOPHYTA. 27 



3. Selaginella apus (L.) Spring. (I. F. f. 101.) Annual, light green, stems 

 Creeping, 2.5-10 cm. long, much branched, flaccid, angled on the face. Leaves 

 minute, membranous, of 2 kinds, 4-ranked, spreading in 2 planes : upper leaves of 

 the lower plane spreading, the lower reflexed, ovate, acute, serrulate, not distinctly 

 ciliate ; leaves of the upper plane ovate, short-cuspidate ; spikes 6-16 mm. long, 

 obscurely quadrangular ; bracts ovate, acute, sometimes serrulate, acutely keeled in 

 the upper half ; macrosporanges more abundant toward the base of the spike. In 

 moist shaded places, often among grass, Me. and Ont. to the N. W. Terr., south to 

 Fla. f La. and Tex. 



Family 3. ISOETACEAE Underw. 



Quillwort Family. 



Aquatic or marsh plants rooting in the mud, with a short buried 2- 

 lobed or 3-lobed trunk (stem) sending out abundant roots and sending up 

 a compact tuft of rush-like leaves. Sporanges sessile in the axils of the 

 leaves, some containing macrospores (macrosporanges), others micro- 

 spores (microsporanges) ; the former germinate into prothallia bearing 

 only archegones, the latter into prothallia bearing usually only a single 

 antherid. The family consists of the following genus only. 



1. ISOETES L. Quillworts. (See Appendix.) 

 Submerged, amphibious or uliginous plants with a cluster of elongated awl- 

 shaped leaves rising from a more or less 2-3-lobed fleshy short stem, the leaves with 

 or without peripheral bast-bundles, with or without stomata, bearing a small 

 membranous organ (ligule) above the base. Sporanges sessile in the excavated bases 

 of the leaves, orbicular or ovoid, the sides more or less covered with a fold of the 

 inner side of the leaf-base (velum). The sporanges of the outer leaves usually con- 

 tain spherical, mostly sculptured macrospores, those of the inner ones contain minute 

 powdery usually oblong microspores. [Name Greek, taken from Pliny, apparently 

 referring to the persistent green leaves.] About 50 species, widely distributed. 

 Owing to their aquatic habitat and apparently local distribution, these plants are 

 popularly little known. 



Submerged or rarely emersed in very dry seasons ; leaves quadrangular, without peripheral 

 bast-bundles. 

 Stomata wanting; macrospores crested. 



Leaves stout, rigid, scarcely tapering. 1. /. lacustris. 



Leaves slender, tapering. 2. /. Tuckermanz. 



Stomata present ; macrospores echinate. 3. /. echinospora. 



Amphibious or submerged only in earlier stages ; stomata always present on the quad- 

 rangular leaves. 

 Peripheral bast-bundles wanting. 



Microspores papillose or tuberculate, not reticulate, white. 



Leaves 5-8 cm. long ; macrospores with minute warts. 4. /. saccharata. 

 Leaves 10-20 cm. long ; macrospores with jagged crests. 5. /. riparia. 

 Microspores densely reticulate and often slightly papillose, dark brown ; macro- 

 spores with thick-walled reticulations. 6. I.foveolata. 

 Peripheral bast-bundles irregular or wanting : submersed leaves very long ; macro- 

 spores with convolute labyrinthine ridges. 7. /. Eatoni. 

 Peripheral bast-bundles present. 



Macrospores sparsely covered with irregular crests. 8. I. Canadejisis. 



Macrospores with honeycomb-like reticulations. 9. /. Engelmanni. 



Terrestrial ; stomata abundant on the triangular leaves. 



Leaves 15-60, usually black at the base. 10. /. melanopoda. 



Leaves 8-12, bright green, paler at the base. 11. /. Butleri. 



X. Isoetes lacustris L. (I. F. f. 102.) Submerged or rarely above water; 

 leaves 10-25, rigid, rather thick, scarcely tapering, dark or olive green, obtusely 

 quadrangular. 5-15 cm. long ; stomata none ; peripheral bast-bundles wanting ; 

 sporange orbicular or broadly elliptic, unspotted ; velum rather narrow ; ligule 

 tr; angular, short or somewhat elongated ; macrospores 500-800 /i in diameter, 

 marked all over with distinct or somewhat confluent crests, and bearing three con- 



