Of the interesting order Liliaceæ we have only one plant of the coast, and even that—the Asparagus—is not by any means generally common. It is the same plant that is so largely cultivated as an article of diet, and which is so highly valued on account of its diuretic properties. It is moderately common on parts of the south coast, particularly in the Isle of Portland and in West Cornwall, and its general appearance is so graceful that it is largely employed as an ornamental garden plant. The stem is erect and freely branched, bearing feathery bunches of bristled leaves and pale-yellow axillary flowers. As is the case with the Liliaceæ generally, the flowers are bisexual, with a six-parted perianth, six stamens, and a three-celled superior ovary; and the last named, in the Asparagus, forms a bright-red berry in the autumn.
We have now to leave the monocotyledonous plants and pass on to the dicotyledons, which form the most highly developed of the primary divisions of the vegetable kingdom. A few of the general characteristics of this group have already been given, but we must now look rather more closely into the nature of the plants included.
The class receives its name from the presence of two cotyledons or seed-leaves in the embryo plant, and is also known as the Exogenæ because the stems increase in thickness by the addition of zones of woody tissue at the exterior. When the young dicotyledonous plant first appears above the ground, the two cotyledons, which formerly served to shelter the immature bud, usually appear as tiny fleshy leaves; but these soon wither away, while the bud produces the more permanent leaves that are of a very different structure. A section of the stem will reveal distinct pith, wood, and bark, the wood being more or less distinctly divided into wedge-shaped masses by rays from the pith; and, in the case of perennial stems, the wood is arranged in concentric rings, the number of which correspond approximately with the years of growth. The leaves of exogens have their veins in the form of a network, and the parts of the flower are generally arranged in whorls of two or five or of some multiple of these numbers.
The flowers always have stamens and pistil, but in some these organs exist in separate flowers, either on the same plant, or on different plants of the same species, and the ovules are nearly always contained in a case called the ovary.
Dicotyledons are divided into three main groups, the division being based on the structure of the flowers. They are the Apetalæ in which the petals are absent, but the perianth is frequently petaloid, though it is occasionally also absent; the Gamopetalæ, in which the petals are united; and the Polypetalæ, in which the petals are always distinct.
Dealing with these divisions in the above order we come first to the Spurges, three species of which occur on sandy shores. They belong to the order Euphorbiaceæ, which includes, in addition to the spurges, a number of herbs, trees, and shrubs with entire leaves often a milky juice, and small flowers, sometimes enclosed in calyx-like bracts. The flowers may have one or several stamens, and the perianth, if present, consists of three or four parts; but perhaps the best distinguishing feature of the order is the nature of the fruit, which separates elastically into three carpels.
Fig. 289.—The Sea Spurge
The Sea Spurge (Euphorbia Paralias) is commonly seen on sandy shores, where its yellow flowers bloom in late summer and in autumn. It may be distinguished among the numerous species of the genus by its narrow oblong imbricated leaves, of a tough leathery nature, the broad heart-shaped bracts, and the wrinkled capsules containing smooth seeds. The Portland Spurge (E. portlandica) is a similar plant, found in similar situations, and flowering from May to September. Its leaves are oval and narrow, obtuse, and of a glaucous colour, and the bracts are more triangular than those of the last species. The capsules are slightly rough, as are also the seeds. There is yet another sea-side spurge—the Purple Spurge (E. peplis)—a somewhat rare plant, found on some of the sandy shores of the south of England. It grows to about eight or nine inches in length, and blooms in late summer, the flowers, like those of most of the spurges, being yellow. The stem is of a glaucous colour, and trails along the ground; the leaves are opposite and somewhat heart-shaped, and the flowers solitary. This species may be distinguished from other spurges by its stipuled leaves.