The stele of Equisetum is of a very peculiar type whose relations are not completely clear.
Hemi-hydrophytes (swamp plants, marsh plants, &c.).Plants riose vegetative organs are partly submerged and partly aerial; lucheria terrestris, Philonotis fontana, Sca pan-ia undulata, Maria spp., Salvinia ivatans, Azolla spp., Equisetum limosum, Typha rgustifolia, Phragmites communis, Scirpus lacustris, Nymphaea tea, Oenanthe fistulosa, Bidens cernua.
Equisetum palustre, Phragmites communis, Glyceria aquatica, Carex riparia, Iris Pseudacorus, Rumex ilydrolapathum, Oenanthe fistulosa, Bidens spp.
At 175° C. it is resolved into water and aconitic acid, C 6 H 6 0 6, a substance found in Equisetum fluviatile, monkshood and other plants.
In the more damp and marshy places the bottom is covered with marsh trefoil, carex, smooth equisetum, and rush.
The Ulvaceae, the thallus of which consists of external form as an expanded Coprinus, Neomeris simulates the laminae, one or more cells thick, or hollow tubes, probably represent fertile shoot of Equisetum with its densely packed whorled branches, a still more advanced stage in the passage of a colony into a multiand in Microdictyon, Anadyomene, Struvea and Boodlea the branches, cellular plant.
The stamens of Araucaria and Agathis are peculiar in bearing several long and narrow free pollen-sacs; these may be compared with the sporangiophores of the horsetails (Equisetum); in Taxus (yew) the filament is attached to the centre of a large circular distal expansion, which bears several pollen-sacs on its under surface.
The finer branches are green, and bear a close resemblance to the stems of Equisetum and to the slender twigs of Casuarina; the surface of the long internodes is marked by fine longitudinal ribs, and at the nodes are borne pairs of inconspicuous scale-leaves.
- The plants of the single living genus Equisetum, which vary in height from a few inches to 40 ft., have subterranean rhizomes, from which the erect shoots arise.
- Equisetum maximum.
Abnormal specimens of Equisetum in which the strobilus is interrupted by whorls of leaves are of interest for comparison with the fructification of Phyllotheca.
In the primary structure of the stem the Calamites present many points of resemblance to Equisetum, but secondary thickening went on in both stem and root.
There is a close resemblance between these sporangiophores and those of Equisetum, but as a rule only four sporangia were borne on each.
Our knowledge of the extinct Equisetales, full as it is with respect to certain types, does not suffice for a strictly phylogenetic classification of the group. The usual subdivision is into Equisetaceae including Equisetum and Equisetites (with which Phyllotheca and Schizoneura may be provisionally associated), and Calamariaceae, including Calamites and Archaeocalamites.