ISOETACEAE. 7 



rangia 1 -celled, in the axils of leaves which are so arranged as to 

 form more or less quadrangular spikes; spores of two kinds, some 

 sporangia (megasporangia) containing four megaspores, others 

 (microsporangia) containing numerous microspores. 



12. SELAGINELLA. 



Sporangia in the axils of leaves forming terminal cone-like 

 spikes; sporangia minute, subglobose, opening transversely; 

 megaspores globose, four in each megasporangium ; microspores 

 small, numerous. 



Selaginella wallacei Hieron. Stems densely tufted, 5-10 cm. long, pros- 

 trate or ascending, much branched; leaves closely imbricate, narrowly lanceo- 

 late, ciliate margined, channeled on the back, tipped with a slender white 

 awn; spikes quadrangular, 1-1.5 cm. long; bracts like the leaves but the awns 

 shorter and the margin more ciliate. Abundant on the basaltic bluffs of 

 Snake River. 



Family 6. ISOETACEAE. 



Plant aquatic, usually submersed or sometimes growing on 

 moist soil, consisting of a short, two or three-lobed fleshy stem 

 with a dense tuft of fibrous roots and a compact cluster of rush 

 or grass-like leaves; sporangia in small lobes enclosed in the 

 bases of the leaves; spores of two kinds, large (megaspores) and 

 small (microspores). 



13. ISOETES. Quillwort. 



Stem a fleshy corm rooting just above the base, surrounded 

 above by the swollen bases of the awl-shaped linear leaves; 

 sporangia large, enclosed in the bases of the leaves; those of the 

 outer leaves with megaspores, those of the inner with micro- 

 spores; the sides of the sporangia more or less covered with a 

 fold of the inner side of the leaf base (the velum). 



Leaves without stomata or bast-bundles; plant submersed, 



with rigid leaves. /. paupercula. 



Leaves with stomata and bast-bundles; plants of shallow water 

 or muddy places, often emersed. 

 Trunk trilobed; leaves setaceous; megaspores with blunt 



spines. /. minima. 



Trunk bilobed; leaves not setaceous. 



Megaspores with scattered low tubercles or fragmentary 



walls. /. howellii. 



Megaspores smooth or with low tubercles or wrinkles. /. melanopoda. 



Isoetes paupercula (Engelm.) A. A. Eaton. (/. occidentalis Henderson.) 

 Trunk bilobed; leaves 40-60 or fewer in small plants, spreading, rigid, quad- 

 rangular, sharp-pointed, dark-green, 10-20 cm. long; velum narrow, covering 

 about one third of the sporangium; megaspores covered with scattered 



