| 1. | Equisetum | maximum. |
| 2. | ” | pratense. |
| 3. | ” | arvense. |
| 4. | ” | sylvaticum. |
| 5. | ” | limosum. |
| 6. | ” | palustre. |
| 7. | ” | hyemale. |
So far we have been describing what is known as the barren stem, because it ends in several unbranched joints, without any fructification. Before these barren stems appeared there arose from the rootstock a stem differing greatly in appearance, usually without branches, and lacking the green colouring matter (chlorophyll). It is pale brown in colour, of stouter build, but much shorter, for whereas the barren stem is about two feet in length, the fertile is only a few inches, or at most less than a foot. The leaf-sheath is longer, and the teeth frequently adhere two or three together. The stem terminates in a kind of cone, consisting of many whorls of flat scales, each supported by a central stalk, on the underside of which are arranged from six to nine capsules containing spores. These spores are very curious: they are globular in form, and invested with several coats, the outermost of which splits into four narrow strips, which are highly hygroscopic, and which remain attached to the spore at one point only. These elaters, as they are termed, are very sensitive to changes in the humidity of the atmosphere, as may be proved by breathing upon them, however slightly, when they will be seen (through the microscope) to be in active movement. In many ferns the spores require months to elapse before germination takes place; those of Horsetails will germinate in a few hours. Owing to its possession of chlorophyll the spore, if not placed in a situation suitable for germination, perishes in the course of a few days.
The name of the genus is from the Latin, equus, a horse, and seta, a bristle. The fertile stems appear in March and April, the barren ones at intervals later.
Lichens (Lichenes). Plate 126.
The rambler will meet with specimens of the Lichen tribes at every turn, when he has got fairly away from the smoke of towns. He will find them on the tree-trunks or rocks and walls, old posts and palings, on thatch and on the ground. Wherever they are found they may be accepted as certificates of the purity of the air. Formerly considered as a distinct type, they are now held by the advanced school of cryptogamic botanists as commensals, or partnerships formed between a fungus and an alga. They are usually thin crusts, consisting of an upper and a lower epidermis, formed of closely crowded cells, and to the lower layer rootlike filaments are attached. Between these layers are two differing elements; a loose stratum of green cells (gonidia), which are said to be algæ, and below these a layer of fungoid threads. The contention of the new school is that these algæ have been captured by a fungus and held in bondage, being forced to elaborate starch by means of their chlorophyll from the inorganic material obtained by the rootlike filaments, which starch the fungus is able to feed upon. Some of the green cells are pushed out from time to time invested with a few wisps of fungus-threads, and so reproduce the partnership. It is but right to add that some good authorities on this branch of botany decline to accept these views, and still regard lichens as independent organisms and not partnerships.
Triangular Moss.
Hypnum triquetrum. Hair-Moss.
Polytrichum formosum.
—Musci.—
