142 OUR NATIVE FERNS AND THEIR ALLIES. 



16. S. Pringlei Baker. Outer stems 3' — 4' long, the inner 

 gradually shorter, flabellately branched, light green above, pale 

 below ; branchlets close, i" — 2" wide ; leaves of the lower plane 

 crowded, oblong, about i' long, including the conspicuous horny 

 white awn ; leaves of upper plane slightly smaller, somewhat 

 oblique ; spikes short with uniform bracts. . Chenate Moun- 

 tains, Texas {Nealley). 



S. pilifera A. Br. is reported by Mr. Baker from Texas, but 

 it has not been found there recently. 



Family 3. ISOETACE/E. 



Plant-body consisting of a.bilobed or trilobed trunk emitting 

 dense tufts of roots, and sending up a compact rosette of rush- 

 like leaves, submerged, amphibious or sometimes growing in 

 moist soil. Sporangia sessile in the axils of the leaves, some 

 containing macrospores and others microspores. Contains a 

 single genus widely distributed. 



I. ISOETES L. QUILLWORT. 



Stem or trunk a more or less depressed, fleshy corm, rooting 

 just above its bilobed or trilobed base, covered above with the 

 dilated and imbricated bases of the awl-shaped or linear leaves. 

 Sporangia large, orbicular or ovoid, plano-convex, very thin, 

 sessile in the axils of the leaves and united at the back with 

 their excavated bases ; those of the outer leaves filled with 

 spherical macrospores ; those of the inner leaves filled with 

 minute and powdery, grayish, obliquely oblong and triangular 

 microspores. Name from Gr. icroi, equal, and ezoi, year. Con- 

 tains about 50 species, of which sixteen are found within our 

 limits. 



Note. — The measurements of the spores are given in millimetres; mm. = .03937 

 inch. 



§ I. Submerged, rarely above water in driest seasons; leaves 

 quadrangular without peripheral' bast-bundles ; velum incom- 

 plete. 



* Stomata absent. 



I. I. laoustris L. Leaves 10 — 25, stout, rather rigid, ob- 

 tusely quadrangular, acute but scarcely tapering, dark or olive- 



