It is now necessary to consider a very striking order of plants. Unlike the Club Mosses, it is probable that most people are familiar with one or more species of Horsetail; some of these plants are not only common, but they are also very striking in appearance. In all there are eight species of _Equisetum_ which are natives of the United Kingdom, and most of these are fairly easy to identify if a few leading features are borne in mind. _Equisetum arvense._ The generic name in this case is composed of two Latin words—_equus_, “a horse,” and _seta_, “a bristle.” Thus we see that the popular name of the plant is an almost exact translation of the scientific one. The specific name is derived from the Latin adjective _arvus_, “a field,” and has, of course, reference to the fact that the plant grows in pastures. The Field Horsetail. [Illustration: Barren stem of Equisetum arvense.] This species is by far the commonest of all the Horsetails, and is very frequently to be found on embankments in fields and by the sides of roads. The plant, which dies down in the winter, starts its growth quite early in the year with the development of the fertile stems. These rise straight up from the branching root-stock, and are generally about five or six inches in height. The stem, which is of a very pale colour, is of rather a succulent nature; it is hollow in the centre and in a certain way reminds one of bamboo. At intervals there are certain sheaths which are divided into a number of teeth with very sharp points. The cone-like fructification is about an inch in length and bears a number of peltate scales to which the spore capsules are attached. The spores are ready for dispersal in the month of May. Just about this time the barren stems put in an appearance. These rise to the height of two feet, or even more, and have many whorls of spreading branches which in their turn may again be branched. It is these branches which carry on the real vegetative work of the plant. For the real leaves we must examine the sheaths, which with their wedge-shaped teeth are to be found at the stem joints. The teeth are the only free portions of the leaves of the Horsetails. It is interesting to note that in each whorl the branches are equal to the number of leaves and are alternate to them. The stem of the barren branches of the Field Horsetail is slightly marked with furrows, which vary in number. The branches are usually only four-furrowed, and have sheaths with the same number of teeth. The whole of the barren portion of the Field Horsetail is very rough to the touch. This is due to the fact that the plant is covered with tiny flinty particles. That the measure has a protective value is very evident, for cattle have hardly ever been known to eat the plant.