TASCTTLARIA. 



417 



stems, bearing whorls of scale-like leaves at the joints, where they 

 are sometimes verticillately branched. Spores borne on metamor- 

 phosed leaf-bearing stems, terminating in a clavate joint covered 

 with dehiscent sporanges. Spores triple-coated, of one kind, with 

 two elastic filaments called elaters, formed by the spiral fission of 

 the outer coat of the spore. Stem, rhizome, and root grow longi- 

 tudinally by means of a single apical cell, giving off three series of 

 segments. Fibro- vascular bundles arranged in a circle. No peri- 

 cambium in the root. Sexual Generation : arising from the spores, 

 consisting of independently subsisting, usually dioecious prothallia, 

 the male prothallia being smaller than the female. Illustrative 

 Grenus : Equisetum, L. 



Structure and Life-history. The ' 



Equisetacece at present existing con- 

 sist of a single genus, Equisetum, a small 

 group of herbaceous plants, growing 

 chiefly in wet places, with a creeping-, 

 subterraneous, jointed but solid rhizome 

 (fig. 494, #), from which arise erect shoots 

 or stems. The stems are striated lon- 

 gitudinally, jointed at intervals, with 

 circles of small and narrow, membra- 

 nous, scale-like leaves at the nodes, and 

 they are fistular like the stems of 

 Grasses. They are also traversed by 

 several air-canals, varying in number 

 and disposition according to the species. 

 The stems are sometimes simple, some- 

 times compound, bearing whorls of 

 branches at the nodes, which branches 

 resemble the main stem in character, 

 and frequently branch again in a similar 

 manner at their nodes. The erect 

 stems are either fertile or barren (meta- 

 morphosed or true) ; in some species the 

 fertile stems are short and simple, while 

 the barren stems are tall and provided 

 with numerous whorls of spreading 

 co mpound branches ( E. fluviatile) . The 

 fertile stems terminate in a kind of club 

 or spike (fig. 494, &), composed of a 

 short axis closely covered with spo- 

 ranges (c) ; these are small peltate or 

 mushroom-shaped bodies (d) attached 

 by their stalks to the central axis, and 

 bearing under the overhanging head a 

 circle of vertical, tooth-like pouches (d), 

 resembling the anther-cells of Thuja among Conifers, which burst by 

 a vertical slit on the inside to emit the spores when ripe. The spores 



2E 



Organization of Equisetaceas: a, fer- 

 tile stem oiEquisetum aryense, arising 

 from the rhizome ; b, fruit-spike (nat. 

 size); c, transverse section of do., 

 showing how the sporanges are at- 

 tached to the axis ; d, a group of 

 sporanges seen from beneath ; e, a 

 spore ;/, the same, with its " elaters " 

 uncoiled ; g, fragment of the branched 

 stem of E. palustre. 



