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.
- This class, represented in the recent flora by the single genus Equisetum, with about twenty species, was one of the dominant groups of plants in Carboniferous times.
The longitudinal course of the vascular bundles and their relation to the leaves in Calamarieae generally followed the Equisetum type, though more variable and sometimes more complex.
Stomata of the same structure as in Equisetum have been detected in the epidermis.
Almost all strobili of the Calamarieae are constructed on the same general lines as those of Equisetum, with which some agree exactly; in most, however, the organization was more complex, the complexity consisting in the intercalation of whorls of sterile bracts, between those of the sporangiophores.
The sporangiophores, which are usually half as numerous in each verticil as the bracts, have the same form as in Equisetum, but each bears four sporangia only.
Equisetum type of strobilus.
An Equisetaceous plant, which Brongniart named Phyllotheca in 1828, is another member of the same flora; this type bears a close resemblance to Equisetum in the long internodes and the whorled leaves encircling the nodes, but differs in the looser leaf-sheaths and in the long spreading filiform leaf-segments, as also in the structure of the cones.
Represented by casts of Triassic age, Equisetites arenaceus and other species, probably possessed the power of secondary growth in thickness; the cones were of the modern type, and the rhizomes occasionally formed large underground tubers like those frequently met with in Equisetum arvense, E.
Equisetites columnaris, a common fossil in the Jurassic plant-beds of the Yorkshire coast, represents another type with relatively stout and occasionally branched vegetative shoots, bearing leaf-sheaths very like those of Equisetum maximum and other Horsetails.
Cones from the Middle Coal Measures, described by Kidston under the name of Equisetum Hemingwayi, but probably belonging to one of the Calamarieae, bear a striking external resemblance to those of recent Equisetum.
The stele of Equisetum is of a very peculiar type whose relations are not completely clear.