Their USES are very limited. A few species, such as E. hiemale are used for polishing on account of the hard siliceous cell-walls of the epidermis, found in all species of Equisetum.
Sub-Class 2. Heterosporous Equisetinæ.
The two orders which come under this head are united by the characteristics, that the verticillate leaves are not united into sheaths (Fig. [226]), and that between each whorl of fertile leaves there is also a whorl of barren ones. The fertile whorls in Annulariæ are situated about midway between the barren ones (Fig. [227]), but in Asterophylliteæ they occur immediately above a barren whorl (Fig. [228]) and contain only half as many members as the latter. The lower whorls bear macrosporangia with one macrospore, the upper, microsporangia with many microspores.
Fig. 226.—A. fragment of Annularia.
Fig. 227.—Fragment of Annularia longifolia, with sporangia; the leaves have partly fallen off: a barren whorls; s fertile whorls.
Fig. 228.—Fragment of cone of Asterophyllites (Volkmannia elongata): a and s as in Fig. [227].
The Annulariæ were distichous (Fig. [226]), and presumably floating plants. The Asterophylliteæ had verticellate branches. These also died out after the Carboniferous period, at the close of the Palæozoic.