348 



PART IV. VEGETABLE TAXONOMY. 



Class I. — The Equisetine^e, or Horsetails. 

 The plants of this Class are readily distinguished by their 

 hollow, cylindrical, jointed and fluted stems, their sheath-like 

 whorls of united leaves, and their terminal, cone-like fructifica- 

 tions. The internodes of the stem are hollow, but each node is 

 closed by a membrane ; the leaf-sheath is broken up into a 

 number of points at its apex, each point corresponding to the 

 tip of a leaf, and for each there is a corresponding fibro-vascu- 

 lar bundle, which at the base of the sheath passes into the 

 stem, thence straight down it to the node 

 next below, where it forks into two, the 

 branches coalescing with those of the stem. 

 The stems are all herbaceous and 

 mostly perennial, from creeping, under- 

 ground stems ; the aerial stems usually 

 perish at the close of the season, but a few, 

 like those of the scouring-rush, Equisetum 

 hyemale, persist over winter. The stems 

 are sometimes simple ; sometimes they are 

 branching, and the branches, which have 

 their origin on the inside of the base of 

 the leaf-sheath, are arranged in whorls. 

 The stems grow from a terminal, triangu- 

 lar-pyramidal cell. 



Fig. 555. Fig. 556. 



Fig. 555. — Portion of Equisetum sylvaticum, showing fruiting cone, a, at the apex of 

 the stem; b, transverse section of stem somewhat magnified. 



Fig 556.— Equisetum sylvaticum, a, fruiting scale, magnified, showing sporangia; b, 

 one of the spores enveloped in the elaters ; c, one of the spores with elaters extended. 



The fruiting cone is either borne on the ordinary vegetative 

 stem, as in Equisetum hyemale, or on a special stem of a little 

 different form set apart for the purpose, as in Equisetum arvense. 



