The Sea Shore

by William S. Furneaux

The first of these includes all the very low forms of vegetable life, the simplest of which (Protophyta) are minute plants, each consisting of a single microscopic cell that multiplies by a process of budding, no sexual organs of any kind being produced. Some of these minute unicellular organisms contain chlorophyll—the green colouring matter of plants, by the action of which, under the influence of light, the plant is enabled to decompose the carbonic acid gas of the atmosphere, using the carbon for the purpose of building up its own substance, and setting free the oxygen into the air again. Others contain no chlorophyll; and these, having no power of feeding on carbonic acid gas, are more or less dependent on organic matter for their supplies of carbon.

Only very slightly removed from these minute plants are the Algæ of fresh and salt water, varying in size from microscopic dimensions to enormous plants, the lengths of which may reach many yards and the weight several stone. They contain chlorophyll, and can therefore avail themselves of inorganic food material; and although some multiply only by repeated subdivision of their cells, others develop sexual organs by the union of which fertilised spores are formed. The nature of these Algæ will be more fully described presently; and we will go no further now than to justify the location of such large and conspicuous plants (as many are) so low in the scale of vegetable life by stating that they are entirely cellular in structure, never producing true vessels such as we see in higher plants; and that though some of them develop parts which more or less resemble the leaves and roots of higher forms, the former are far more simple in structure and function than true leaves and the latter are never engaged in the absorption of food from the soil to which they are fixed.

Another important group of the Thallophytes is formed by the Fungi, which include the familiar mushrooms, toadstools, and the sap-balls so commonly seen on decaying trees; also the smaller forms known as moulds, mildew, and smut. These, also, are entirely cellular in structure; and, since they develop no chlorophyll, are compelled to live as parasites on living beings or to derive their food from decaying organic matter. Thus they are the creatures of corruption, their presence always denoting the breaking down of living matter or of matter that has previously lived.

Now leaving the Thallophytes, and passing over the small group of aquatic plants known as the Charales, we come to the Muscineæ, which contains the Liverworts (Hepaticæ) and the Mosses (Musci).

The plants of both these groups require much moisture, and are found principally in damp, shady situations. Like the preceding groups they are cellular in structure, never producing true vascular bundles such as the higher plants possess; and their life histories are rendered interesting by the ‘alternation of generations’ which they exhibit. The first generation is a sexual one produced from the spores, and consists either of a mass of delicate threads from which a plant with a leafy axis is developed by a process of budding, or of a little green frond (the thallus). These bear the male and female elements, called respectively the antheridia and the archegonia; and when the central cells of the latter are fertilised by the former, they give rise to a case, with or without a stalk, containing a number of spores. When the case is ripe, it opens horizontally by means of a lid, thus liberating the spores.

Following these in the ascending scale are the Vascular Cryptogams, in which some of the cells become modified into true vessels. Here, too, the plants exhibit a distinct alternation of generations, the spore first giving rise to a small, leafless body, the prothallium, which bears the sexual organs; and then the female elements, after fertilisation, produce the spore-bearing plant.

This group contains quite a variety of beautiful and interesting plants, including the Ferns (Filicales), Horsetails (Equisetales), Club-mosses (Lycopodiales), Water Ferns (Rhizocarpeæ), and Selaginellales.

Ferns usually produce their little green prothallia above ground, and the perfect plant generally has a creeping rhizome or underground stem. Some, however, have strong, erect, woody stems, such as we see in the tree ferns of tropical and sub-tropical countries. The horsetails and the club-mosses are also produced from prothallia that are formed above ground. The perfect plants of the former have branching underground stems which give off numerous roots, and send up annually green, jointed, aërial stems that bear whorls of fine leaves, each whorl forming a toothed, ring-like sheath. The fertile shoots terminate in cones, on the modified leaves of which the sporangia are produced. The stems of the club-mosses are clothed with small overlapping leaves, in the axes of which the sporangia are produced; and the spores, which are formed in abundance, constitute the lycopodium powder with which druggists often coat their pills.

Water ferns either float on the surface of water or creep along the bottom, and produce their fruit either at the bases of the leaves or between the fibres of submerged leaves. The Selaginellas are characterised by a procumbent stem that branches in one plane only, producing small, sessile leaves, with a single central vein. A number of roots grow downward from the under side of the stem, and the fruit is developed in the axils of the leaves that form the terminal cones of the fertile branches.

The above are all the principal divisions of the flowerless plants, and we have now to note the general characteristics of the Phanerogams. The chief of these is, of course, the possession of flowers as reproductive organs; and although it is not convenient to give a full description of the flower at the present time, it will be necessary to say a little concerning it in order that we may be able to grasp the broad principles of classification.