698 SELAGINELLACE.E. 



are on opposite sides all along the spike. (Name a diminutive of Selago, an 

 ancient name of a Lycopodium, from which this genus is separated, and which 

 the plants greatly resemble in habit and foliage.) 



* Leaves all alike and uniformly imbricated ; those oj the spike similar. 



1. S. Spin6sa, Beauv. Sterile stems prostrate or creeping, small and 

 slender; the fertile thicker, ascending, simple (1-3' high); leaves lanceolate, 

 acute, spreading, sparsely spinulose-ciliate. (S. selaginoides, Link.) Wet 

 places, N. H. (Pursh), Mich., Lake Superior, Colorado, and northward; rare. 

 Leaves larger on the fertile stems, yellowish-green. (Eu.) 



2. S. rupestris, Spring. (PI. 21, fig. 1-4.) Much branched in close 

 tufts (13' high); leaves densely oppressed-imbricated, linear-lanceolate, con- 

 vex and with a grooved keel, minutely ciliate, bristle-tipped; those of the 

 strongly quadrangular spike rather broader. Dry and exposed rocks ; very 

 common. Grayish-green in aspect, resembling a rigid Moss. Very variable 

 farther west and south. (Eu.) 



* * Leaves shorter above and below, stipule-like ; the lateral larger, 2-ranked. 



3. S. apus, Spring. Stems tufted and prostrate, creeping, much branched, 

 flaccid; leaves pellucid-membranaceous, the larger spreading horizontally, 

 ovate, oblique, mostly obtuse, the smaller appressed, taper-pointed ; those of 

 the short spikes nearly similar ; larger spore-cases copious at the lower part 

 of the spike. Low, shady places ; not rare, especially southward. A deli- 

 cate little plant, resembling a Moss or Jungermanuia. 



2. ISOETES, L. QUILLWOBT. (PI. 21.) 



Stem or trunk a fleshy more or less depressed corm, rooting just above its 2- 

 lobed (or in many foreign species 3-lobed) base, above covered with the dilated 

 and imbricated bases of the awl-shaped or linear somewhat quadrangular 

 leaves, which include four air-tubes, intercepted by cross partitions. Sporangia 

 pretty large, orbicular or ovoid, plano-convex, very thin, sessile in the axils of 

 the leaves, and united at the back with their excavated bases (the thin edges 

 of the excavation folding round partly cover them, forming the velum), trav- 

 ersed internally by transverse threads ; those of the outer leaves filled with 

 large spherical macrospores, their whitish crustaceous integument marked by 

 one circular, and on the upper surface by three radiating elevated lines (circum- 

 scribing a lower hemisphere, and three upper segments which open valve-like 

 in germination) ; those of the inner leaves filled with very minute and pow- 

 dery grayish microspores ; these are always obliquely oblong and triangular. 

 -Mostly small aquatics, grass-like or rush-like in aspect, some always sub- 

 merged, others amphibious, a few living in merely moist soil, maturing their 

 fruit in late summer and early autumn, except n. 7 and some forms of n. 6. 



This genus is left essentially as it was elaborated for the 5th edition by the 

 late Dr. GEORGE ENGELMANN. The present editor has added to the range 

 of a few species, and given var. robusta of n. 3. 



* Growing under water, only accidentally or in very dry seasons out of water; 



leaves without stomata (except informs ofn. 3) and peripherical bast-bundles. 



1. I. laciistris, L. (PI. 21, fig. 1-5.) Leaves (10-25 in number, 2-6' 

 long) dark green, rigid ; sporangium ovoid or circular, the upper third, or less, 



