ORDER 158. EQU1SETACEJS. 



415 



branchlets crowded, chert, 2" wide; leave? crowded, oblong, entire, obtuse, the 

 smaller ones with an -uncinate (reflexed) slender point. 



7 S. SERPENS. Stems prostrate, with hair-like rootlets, 2-3-pinnate ; branchlets short and 



crowded, 1" wide ; IVB. crowded, round-ovate, cordate, obtuse, entire, the smaller acute. 



8 S. DELicATfssiMA. Sts. creeping, 5 8', rooting, filiform, loosely 2-3-pinnate, 1" wide; 



leaves ovate, obtuse, ciliate, not crowded, the middle ones scarcely smaller, acute. 



9 S. CAULESCENS. Glabrous, suberect, 1218', 3-4-pinnateiy branched, fern-like, and lan- 



ceolate in outline ; branchlets close, 1|" wide ; leaves close, ovate, entire, very acute, 

 the points turned upward ; smaller leaves mucronate ; stem straw-colored. 



10 S. WILLDENOVII. Like the last as to stems and brandies, but they are finely pubes- 

 cent, and the leaves are less crowded, ovate, and obtuse. 6 12', ovate in outline. 



1 1 S. ERYTHROPU8. Stems red, with scattered, appressed leaves ; frond wide-sprenci, 

 somewhat palmate, with crowded branchleis and leaves, branchlets 1J" wide ; leaves 

 ovate-oblong, oblique, obtuse, ciliate, the smaller with long straight points. 



12 S. CUSPIDATA. Stem or frond 36', densely and somewhat dichotoinously branched , 

 branchlets 1" wide ; leaves closely imbricated, all nearly alike, elliptical, ciliate, 

 bristle-pointed, with the point inclined upward. A variety (perhaps the fertile stems) 

 are lanceolate in outline, 2-3-pinnately branched. 



1 3 S. LEPIDOPHTLLA, Jiesutrection Mots, is a roundish ball when dry. In a cup of water 

 it soon expands into a dense circle of dark-green, densely 2-3-pinnate fronds, with 

 innumerable oval, obtuse, entire leaves. From Lower California. 



3. PSILOTUM, II. Br. Sporangia sessile, 3-celled, imperfectly 3-valved 

 by terminal chinks, filled with farinaceous spores. Stem fork-branched, 

 with alternate, minute leaves, as if leafless. 



P. triqnetrnm Swtz. Stem erect, 8 1(X, many times forked, and, with the branches. 

 -angled : leaves remote, f ' ; fruit 3-lobed, sessile along the branches. E. Pl 



OKDER CLVIII. EQUISETACE^E. HORSETAILS. 



Plants leafless simple stems, or with whorled branches. Steins striate- 

 aulcate, jointed, fistular between, and separable at, the joints. Sheatlit 

 dentate, crowning each in tern ode. Fructification a dense, oblong-cylin- 

 dric, terminal, and cone-like spike, composed of 6-sided, peltate scales, 

 arranged spirally, bearing beneath 4 7 spore-cases, which open laterally. 

 Spores globular, each with 4 elater* attached, involving them spirally, 01 

 open when discharged. (See Figures.) 



EQUISETUM, L. SCOURING 

 RUSH. Character the same as 

 that of the order. The sheaths 

 may be regarded as a whorl of 

 united Ivs. The cuticle abounds 

 in silex. 



555, Equisetum arvense. 556, E. sylvati- 

 cum. 557, Section of the spike, enlarged. 558, 

 A peltate scale with 7 sporanges beneath (or 

 one compound sporange), magnified. 559, A 

 f|n>re with its elaters highly magnified. 



$ Species fruiting in Spring and decaying before the following Winter. . .(a) 

 J Species fruiting in Summci and lasting through the following Winter . .(6) 



