Part 23
The other, numbered 7 on Plate VIII, is the Yellow Oat Grass (_A. flavescens_), which grows to about the same height, and flowers at the same time. In this species the radical leaves are hairy, and also terminate suddenly in a sharp point. The panicle is much branched, with erect spikelets of five or six flowers. In this one, too, the inner glumes have three ribs, but it may be distinguished from the last by the two terminal bristles of the inner scales, and by the blunt ligules (appendages at the base) of the sheathing leaves.
XIX
BY THE RIVER SIDE
We have already dealt with flowers that grow in various damp situations, as moist meadows, woods, &c.; but there are a few such which seem to be particularly partial to the banks of rivers, streams, and ditches: short descriptions of these will be placed separately in the present chapter.
It will be understood from the foregoing remark that the species taken here form only a small proportion of the flowers that actually grow by the river side; for although the numerous species commonly seen in moist fields and meadows may flourish quite to the water's edge, yet there are not many which require the extreme wetness of soil that restricts them to the sodden banks of rivers and streams.
Our first example is the Common Meadow Rue (_Thalictrum flavum_). It belongs to the order _Ranunculaceæ_, but its pale yellow flowers do not, at first sight, suggest a resemblance to the buttercups, anemones, and other favourite flowers of this group, for they have no petals, very small sepals, and are rendered conspicuous only by their densely-clustered stamens, with their long, projecting, bright yellow anthers. The plant is erect, from two to four feet high; and flowers during July and August.
Passing over the Monk's-hood (_Aconitum Napellus_), so well known as a garden flower, which is occasionally seen wild near the banks of streams and ditches, we come to the Blue Meadow Crane's-bill (_Geranium pratense_)--one of the several species of pretty Wild Geraniums (order _Geraniaceæ_). It is a downy plant, varying from one to four feet high, with an erect stem, swollen at the nodes; and opposite, roundish leaves, deeply divided into five or seven lobes with sharp segments. The flowers are of a bluish purple colour, an inch or more in diameter, usually arranged two on a stalk, the two pedicels spreading while in flower, but turned downwards when in fruit. The five sepals have long points, and the five petals are slightly notched. As in other species of the genus there are ten stamens, five shorter than the other five; and a five-lobed ovary, with an equal number of long styles, all attached to a long, central beak. The five carpels separate when ripe, and are raised by the curling of their styles. This flower is common in wet meadows, especially in the southern counties, and is usually more frequent along the banks of rivers and ditches, but it is sometimes also seen in wet thickets. It flowers in June and July.
The Hemp Agrimony (_Eupatorium cannabinum_), of the order _Compositæ_, is very common along the banks of streams and on the borders of wayside ditches all over Britain. It would hardly be taken for a composite flower by those who are acquainted only with the more typical members of the order, but an examination of its rather dull lilac blossoms will soon reveal its affinity to the other members of the group, for the compact, terminal corymb is formed of numerous small heads, each consisting of about five tubular, perfect florets of equal size, surrounded by an involucre of a few overlapping bracts, and remarkable on account of their projecting styles, which are deeply divided into club-shaped branches. The plant is a large one, with erect, reddish stems, varying from two to six feet in height; and it flowers from July to September.
We have already noticed the Lesser Skull-cap (p. 275), which is rather common on damp heaths, and there is another British member of the same genus--the Common Skull-cap (_Scutellaria galericulata_)--that is frequently seen on the banks of streams and in other wet places. The latter is a slightly downy plant, with a creeping stock, and a slender, branched stem from eight to sixteen inches high. Its leaves are opposite, as in other plants of the same order (_Labiatæ_), with very short stalks, and crenate or slightly-toothed edges. The flowers are in pairs in the axils of the leaves, almost sessile, and all turned towards the same side of the stem. On the back of the two-lipped calyx is a hollow, scale-like projection which gave rise to the popular name, for when the corolla falls, the lips of the calyx close over the ripening fruit, and the projection above mentioned then presents somewhat the appearance of a cap. The corolla is over half an inch long, of a dull blue colour without, but much paler inside. This plant flowers from July to September.
On the banks of streams and ditches we may often meet with the Comfrey (_Symphytum officinale_)--a coarse and rough but pretty plant belonging to the _Boraginaceæ_. It has a stout, branching stem, two or three feet high; and the stem-leaves extend downward on its surface forming wing-like ridges. The lower leaves are stalked, broader than the upper ones, generally from six to eight inches long; and all the leaves are rough with bristly hairs. The flowers are of a yellowish white or, sometimes, of a purple colour, and are arranged in forked, drooping, one-sided racemes. The calyx is deeply cleft into five lobes; and the corolla consists of a tubular portion, the top of which is closed by five narrow, fringed scales; and, above this, a wider bell-shaped part, of about the same length, with five small, reflexed teeth. This plant blooms during May and June.
The Yellow Loosestrife (_Lysimachia vulgaris_), of the order _Primulaceæ_ is a beautiful river-side plant, common in most parts, flowering during July and August. Its stem is stout, erect, branched, slightly downy, from two to three feet high; and its leaves are ovate or lanceolate, sessile, and arranged in opposite pairs or in whorls of three or four. The flowers are rather large, of a bright yellow colour, dotted with orange, and arranged in a large, pyramidal, leafy panicle. The calyx is deeply cleft into five pointed segments with hairy margins; and the broadly bell-shaped corolla is deeply divided into five wide lobes. All the five stamens are united by their filaments, forming a kind of cup around the ovary.
There is another beautiful Loosestrife--the Purple Loosestrife--that is often seen on river-banks; but as it is not particularly partial to this habitat, but rather grows in marshes and wet places generally, it is described in another chapter (XV). It should be noted, however, that the two plants are not so nearly allied as the popular names suggest; for while the one described above is of the Primrose family, the latter is a member of the _Lythraceæ_, and differs in having a corolla of free petals.
Passing now to the order _Polygonaceæ_ we have to note the Great Water Dock (_Rumex Hydrolapathum_)--a smooth plant, varying from three to six feet in height, much resembling other Common Docks in general appearance, but found almost always on the borders of streams and ponds. Its leaves are lanceolate in form, usually pointed, and either flat or slightly curled at the margins. The upper ones taper down into the stalk; but the lower ones, which are from one to two feet long, are often heart-shaped at the base. The reddish-green flowers are closely-whorled, and form long panicles. The perianth is cleft into six parts, of which the three outer are smaller and covered with little tubercles, while the inner become enlarged and close over the triangular fruit. Each flower has six stamens and three very short styles. This plant is in flower during July and August.
A few species of Willows and Sallows that grow on the banks of streams belong to the order _Salicaceæ_, and have the following features in common:--Their leaves are simple, stipulate, and deciduous. The flowers are imperfect, in erect catkins with small scales at the base, the male and the female flowers being produced on separate trees or shrubs. Each male flower consists only of a small scale and two or more stamens; and the female of a similar scale, and a conical ovary of one cell with a forked style. The fruit is a conical capsule of two valves, containing several seeds that are covered with white, silky hairs. The species referred to are the Almond-leaved and the Bay-leaved Willows, the Dark-leaved Sallow, and the Purple Osier, but we refrain from introducing descriptions since the identification of these trees is somewhat difficult for a beginner.
XX
ON WALLS, ROCKS, AND STONY PLACES
Several of our flowering plants are to be seen most frequently on walls and rocks, or in other situations where there is hardly a trace of soil of any kind. Some of these thrive in such dry spots, with often such free exposure to the rays of the spring or summer sun, that it is difficult to understand how they manage to survive the periods of drought through which they live until we become acquainted with certain peculiarities of their form and structure.
In the first place we must recall the fact that plants lose a considerable amount of moisture by evaporation from the transpirating surfaces of their leaves, and that this loss must necessarily be greatest when the air is warm and dry unless there is some means by which the transpiration is automatically regulated according to the requirements of the plant and to the varying conditions under which it has to exist.
The leaves of plants are covered with a thin skin or _epidermis_ which consists of a single layer of cells, and which is practically impermeable to moisture. In this epidermis, however, on one or both sides of the leaf, are minute pores (_stomata_) through which water vapour is free to pass; and beneath the porous epidermis is a loose, cellular tissue, with air-spaces, from which the moisture can readily pass, in the form of vapour, to these stomata.
Each of the stomata is bordered by a pair of crescent-shaped _guard-cells_, placed with their concave sides towards each other, and joined at the ends. Further, the guard-cells are capable of changing their form, becoming straighter, and thus reducing or even closing the aperture between them; and becoming again curved, opening or enlarging the pore. The former change takes place during darkness, thus preserving the plant from the cooling effects of evaporation during the chilly nights; and also during dry weather when the plant is in danger of losing much more moisture than the roots can absorb.
So far, however, we have been dealing with a regulating process that is common to green plants in general; but we must look for some additional protection against loss of moisture in the plants which grow in such places that they have to live through longer or shorter periods during which the roots have little or no moisture within reach.
From what has been said concerning the structure of the leaf it will be understood that, as a rule, the larger the surface the greater will be the loss of water in a given time. But when we examine the leaves of the plants that grow on dry walls and rocks, we frequently find that they are more or less thick and fleshy--that the material of the leaf is disposed in such a manner as to reduce the area of the surface as compared with other leaves made up of the same amount of tissue.
In some species this diminution of surface is carried to the extreme, and the leaves have become very thick, assuming a cylindrical or almost globular form; and such leaves are capable of absorbing and retaining large supplies of water that serve to maintain the plant during those periods in which the roots have no moisture within their reach.
We also find that many of the plants in question are further protected from a dangerous loss of moisture by the peculiar arrangement of their leaves, which are often so closely applied to the stem, or so closely overlapping one over another, that the total area of exposed surface is considerably reduced; and it frequently happens that the stem of the plant becomes thick and succulent, as well as the leaves, thus adding to the store of moisture kept in reserve for the rainless days.
While some plants are almost invariably found in dry, stony places, others are very diverse in their habitats, sometimes growing in moist and shady places, and sometimes on cliffs or other rocky situations. In the latter we often find considerable modifications of size, form and structure, the same species being more or less luxuriant and thin-leaved when in damp soils, while in rocky places it becomes more or less stunted, with a tendency to produce thick and succulent leaves.
A few of the plants that we include in the present chapter are to be found only on wet rocks, and are therefore of a nature very different from that of the species growing in dry places. They are always well supplied with moisture; and, being usually surrounded by a damp atmosphere, they lose but little water by evaporation, and thus require no reserves within their leaves or stems.
Our first species is the well-known Wallflower (_Cheiranthus cheiri_), of the order _Cruciferæ_. It is a rather shrubby plant, frequent on old walls and ruins, where it flowers during April and May. Though too familiar to need any description, we may note that in the wild state it varies from six to twelve inches high, and bears sweetly-scented, yellow or orange flowers. The plant is not indigenous, but has now become naturalised as a wild flower in most parts of Britain.
The Wall Rocket (_Diplotaxis tenuifolia_ or _Brassica tenuifolia_), of the same order, is a very similar plant, growing in similar situations, but it does not commence to flower till the summer is somewhat advanced. Its stem is leafy, branched, smooth, woody towards the base, but more slender than that of the Wallflower; and its very variable leaves are generally three or four inches long, deeply divided pinnately into narrow segments with irregularly-toothed margins, and emit a rather unpleasant odour when rubbed. The flowers are of a pale yellow colour, fragrant, about three-quarters of an inch in diameter, in terminal racemes, with sepals more or less spreading; and the fruits are narrow, flattened siliquas, with membranous valves, about an inch and a half long. The plant is to be found principally in the southern counties of England, and flowers from July to September or early October.
On dry rocks, chiefly in the hilly and mountainous districts of North and West Britain, we meet with the Vernal Sandwort (_Arenaria verna_) of the order _Caryophyllaceæ_. This is a little tufted plant, only from two to four inches high, with branched stems more or less decumbent at the base; and small, sessile, opposite, very narrow leaves, each with three veins. The starlike, white flowers are about a third of an inch across, on slender stalks, and grouped in terminal, loose, few-flowered cymes. They have five pointed sepals, less than a quarter of an inch long, each with three prominent veins; five spreading petals, a little longer than the sepals; ten stamens; and a superior ovary with three narrow styles. The fruit is a short ovate capsule which opens, when ripe, by three valves.
One of the Geraniums--the Shining Crane's-bill (_Geranium lucidum_)--is almost essentially a plant of walls and rocks. It is a beautiful species, smooth and shining in all its parts, with a tendency to turn red, like the Herb Robert; and, as in other plants of its order (_Geraniaceæ_), distinguished by the swollen joints of its stem. The leaves are almost round in general outline, but are deeply divided into five, broad, coarsely-toothed segments. The flowers are small, rose-coloured, and generally grow in pairs on axillary stalks. They have five, erect, wrinkled sepals, with long points; and five short, rather broad, entire petals. This species is common in most parts of Britain. It varies in height from six to eighteen inches, and flowers from May to September.
We have now to consider a few species of the order _Crassulaceæ_, which includes some very interesting succulent plants that are peculiarly adapted to a life in the dryest of situations on walls, roofs, &c. In addition to the thick, fleshy nature of their stems and leaves, these plants are distinguished by terminal cymes or corymbs of flowers with (usually) five sepals, the same number of distinct petals, twice as many stamens arranged in two whorls, and carpels equal in number to the petals. Three of the plants referred to are known as Stonecrops, and may be recognised by the following descriptions:--
1. The English Stonecrop (_Sedum anglicum_).--A smooth plant, two or three inches high, abundant in rocky and stony places, especially in the West and near the sea, flowering from June to August. Its stems are more or less decumbent, much branched and rooting at the base; and its leaves are small, thick, almost globular, of a pale green colour with, often, a tinge of red. On the small flowerless branches the leaves are very crowded and overlapping; but on the taller, flowering stems they are more scattered and placed alternately. The little starlike flowers are white, frequently tinged with pink or spotted with red, and arranged in a short, two-forked panicle. They have short, green sepals; narrow, sharply-pointed petals about twice the length; and stamens with bright red anthers.
2. The White Stonecrop (_S. album_).--A somewhat similar plant, from three to seven inches high, sometimes seen in large clusters on rocks, walls, and roofs, bearing white or pinkish flowers during July and August. The whole plant is smooth; and its short creeping stock gives rise to short barren stems with crowded leaves, and erect flowering stems with scattered leaves. The leaves are very thick, of a bright green colour, about a third of an inch long, and oblong or cylindrical in form. The panicles are much branched, with, usually, reddish stems; and each consists of numerous flowers with short, blunt sepals, and narrow, oblong petals about three times as long. This species is not so common as either the last or the following.
3. The Biting Stonecrop or Wall Pepper (_S. acre_).--A smooth plant, of a yellowish green colour, biting to the taste, very common on rocks, walls and roofs, bearing golden yellow flowers during July and August. It has short, barren stems, covered with closely-overlapping leaves arranged in six rows; and erect flowering branches from two to four inches in height. The leaves are very small, thick, succulent, oval or almost globular in form. The flowers, which are in small, terminal, three-cleft panicles, have very short, blunt sepals; and much longer, narrow, pointed petals.
The same order (_Crassulaceæ_) includes the House Leek (_Sempervivum tectorum_)--a plant which has been introduced into Britain, and is now commonly seen growing wild on rocks and on the roofs of country houses. Its spreading offsets give rise to globular tufts of flowerless shoots, and to thick, succulent, flowering stems that grow to a foot or more in height. The lower leaves are ovate, acute, thick, fleshy, edged with red, and arranged in a dense rosette; and the flowering stem, with its sessile leaves, is covered with a short, sticky down. The flowers are of a dull pink or purple colour, and are sessile along the spreading branches of the stem. They have usually about twelve short sepals; the same number of pointed petals, two or three times the length of the sepals; about twice as many stamens; and an ovary of as many carpels as there are petals and sepals. It is interesting to note that half the stamens--those forming the inner whorl--produce no pollen, and that their anthers are often modified into ovaries, the ovules of which, however, do not mature. This plant flowers in July and August.
Our last selection from this order is the Wall Pennywort or Navelwort (_Cotyledon umbilicus_)--a peculiar plant, common on rocks and walls in the South and West of England. It has a hard stock, producing an abundance of fleshy leaves early in the year, and flowering stems, from six to eighteen inches high, from June to August. The lower leaves are round, wavy, smooth, very succulent and brittle, and depressed in the centre where the long fleshy stalks are attached. Those of the stem have shorter stalks which are more and more removed from the centre from below upwards. The stem is thick and succulent, and bears a long raceme of pendulous yellow-green flowers on short stalks. Each flower has a very small calyx of five sepals; a cylindrical corolla, about a quarter of an inch long, with five short teeth; ten stamens, attached to the tube of the corolla; and a superior ovary.
Several of the Saxifrages grow in rocky and stony places, and four or five species are sufficiently common to demand a notice here. The flowers of this group have a calyx of five sepals that is either quite free or more or less adherent to the ovary; a corolla of five petals; ten stamens, attached with the petals at the base of the calyx; and a two-celled ovary, with two distinct styles, containing several seeds.
Our first species is the London Pride, None-so-Pretty, or St. Patrick's Cabbage (_Saxifraga umbrosa_), a native of Irish mountains which has been introduced into Britain as a garden flower, and has now become established as a wild flower in many parts. Its flowering stem grows from six to twelve inches high; and the small white or pink flowers bloom during June and July.
The Starry Saxifrage (_S. stellaris_) is a somewhat similar plant, but much smaller, rarely exceeding six inches in height. It is frequent on wet rocks in the North, flowering in July and August. Its leaves are sessile, oblong or obovate, tapering towards the base, thin, and arranged in spreading rosettes; and the stem is leafless with the exception of little bracts at the base of the pedicels. The starlike flowers, larger than those of the last species, are white, with two yellow spots on each petal, and are arranged in a loose panicle on spreading pedicels. The calyx is adherent to the ovary only at the base, with its segments turned down on the pedicels; and the petals are narrow and spreading.
Another Northern species--the Yellow Mountain Saxifrage (_S. aizoides_)--is abundant on the wet rocks of mountainous districts, flowering from June to September. It is a tufted plant, with branched, decumbent, leafy stems, about six inches long; and crowded, narrow, fleshy leaves, about half an inch long, fringed with hairs at the base. The flowers are yellow, in a loose panicle. The calyx is yellow, like the petals, but much shorter, and erect; and the ovary is adherent to the short tube of the calyx to about half way up.