« PredošláPokračovať »
of the petal. The pistil in the centre exhibits an ovary, surmounted
which occurs on every road-side, observe the lower leaves divided laterally, the stem-leaves more or less shaped like an arrow where they join the stalk, the flowers on short stalks coming off from a common axis and expanding from below upwards (i.e. the lowest opening first), the flowers consisting of four calycine leaves alternating with four white petals arranged like a cross (hence called cruciform or cross-bearing); the stamens, six in number, of which four are longer than the two others (a very important character in cruciform plants, Fig. 21, p. 222); the pistil, consisting of a green, wedge-shaped body, which, as it enlarges and becomes the fruit, assumes a purse-like shape (hence the name of the plant); the pod which forms the fruit opening by two boat-shaped pieces or valves, and leaving in the centre a thin partition, to the edges of which the seeds are attached.
4. THE PEA.–Again, we may take a common pea, and notice its compound leaves with two leaflets at their base, called stipules ; then the five-lobed calyx, and the five parts of the corolla—the large one, which is folded over the others in the bud, being the standard, the two side ones the wings, and the lower one formerl of two which united form the keel. Within this keel are concealed the essential organs of reproduction—the stamens and pistil. The stamens are ten in number, either united into one complete tube by their filaments, or nine of them are thus united, and one is separate. The pistil is the young pod, consisting of ovary, style, and stigma. The pod when ripe is called a legume, and it opens on each side, so as to scatter the seeds which are attached along one side, viz., that next the axis. The name given to the pod is the origin of that applied to the pea family, viz., Leguminous.
5. TRE DANDELION.-Next take the common dandelion as an object of study. In it we have a tapering root yielding a milky
juice, which is used medicinally. The leaves arise from a short stem, forming the crown of the root. These leaves have a peculiar form called runcinate, from their resemblance to a coarse saw, with the marginal divisions pointing downwards towards the root. From the centre of the leaves arises usually one hollow delicate stalk, which ends in a yellow head. This head is not a single flower, like the butter-cup, but a congeries of little perfect flowers of a peculiar form called ligulate or strap-like. Surrounding the flowers is a set of small green leaves called bracts, or flower-leaves.
Next examine the flowers. They are placed on the round expanded summit of the stalk, or on what is called the receptacle. The yellow flowers have at the base a small single-seeded fruit, surmounted by a hairy ring, which is in reality the upper part of the calyx, the lower part being closely united to the fruit. Within this is the corolla, consisting of five united petals, which are split in such a way as to spread out in a strap-like form on one side. Next the row of five stamens is seen, with their anthers united into a tube round the style. In the centre is the pistil, consisting of an ovary below, with a single ovule, then a style, and a two-cleft stigma. The ovary and ovule, when mature, form the fruit and seed, the former being incorporated with the lower part of the calyx. The hairy, or as it is called pappose, upper part of the calyx elongates into a stalk, having the hairs expanded at its extremity, and when the fruit is fully ripe, the various hairy calyces form a globular head.
The receptacle into which the flowers are inserted is at first succulent, and contains a milky juice for the nourishment of the flowers, but it finally becomes dry, and assumes a convex form on the top, while at the same time the bracts are turned downwards. Thus it is that a beautiful provision is made for the scattering of the fruit by the agency of the wind. When mature, the slightest breeze carries off the hairy fruit, which is wafted by its calycine parachutes to a distance, and deposited in a soil fit for its germination. The fruit and seeds of thistles are dispersed in a similar way, and hence the noxious quality of these weeds, which since the curse pronounced on the earth have been brought forth abundantly.
6. THE DAISY.—The daisy supplies an illustration of a flower belonging to the same order as the dandelion. In it we want the marked pappose calyx, but we have a receptacle at the end of the stalk, bearing a number of white, strap-shaped flowers at the margin, each enclosing a pistil, and no stamens, and in the centre regular yellow flowers, each having stamens and pistil,—the pollen from the stamens of the central flowers fertilizing the ovules of the marginal flowers. The receptacle of the daisy becomes ultimately dry and of a conical shape, and thus scatters the fruit. The last two plants having numerous flowers on a common head, and with their anthers united, are called composite, and they constitute a large proportion of the plants of the globe. Besides the weeds noticed, we have familiar instances in the groundsel, the ragwort, the hawkweed, the burdock, the sow-thistle, the colt’s-foot, and the asters.
Monocotyledonous Plants.-(Endogenous and Phanerogamous.)
1. TULIP.To illustrate the monocotyledonous plants, gather a tulip and examine its various parts. First there is underground a thickened bulb-like body, with thinnish brown scales outside, and a solid mass within. This is an underground stem or corm. It produces lateral buds by which the plant is propagated. The corm gives off roots from its lower surface, and a leaf-bud from its upper part ; this bud expands into the parallel-veined leaves. In the centre is produced the flower supported on a long stalk. The parts of the envelope are all alike coloured ; these are six, viz. three external, representing a calyx, and three internal alternating, representing a corolla. Next there are six stamens, with anthers containing pollen, and filaments; and finally, a pistil, consisting of an ovary containing ovules, and a three-lobed stigma at the top of it. The fruit consists of three parts, as may be seen by cutting the mature ovary transversely. In this instance, the envelopes and stamens are evidently placed below the pistil, and are said to be inferior, i.e., below the ovary. This is an important distinguishing character.
7. DAFFODIL.---As another example of a monocotyledonous plant we may take the common narcissus or daffodil, so abundant in our gardens in spring and early summer. Here there is a bulb or underground stem, bearing scales and a bud above, and roots below. Such bulbs and underground stems are common among monocotyledons. From this bulb arise the long, narrow, parallelveined leaves, which contain much viscid matter in their cells, and
abound in spirals, easily seen on rupturing the leaf. The flowering stalk rises from the centre, and bears a single flower at
This flower shows the arrangement according to the number three, or the ternary symmetry. The yellow floral envelope shows six divisions, three exterior, three interior ; and besides, there is a peculiar cup-like ring in the centre which is an extra appendage to the flower, and is called a crown. The stamens are six, thus also a multiple of three. The pistil consists of its three parts, the ovary which is united with the floral envelope, and is seen in the form of a rounded greenish swelling below the flower, the style and stigma seen inside the flower. The fruit consists of three parts, enclosing the seeds, as may be seen by cutting the mature ovary across. In this plant the envelopes and stamens appear above the ovary, and are called superior. This is an important distinguishing character.
Acotyledonous Plants.—(Acrogenous and Cryptogamous.)
1. FERN.—As illustrations of acotyledonous plants we may take a fern and a moss. The common male fern shows the acrogenous stem made up of the bases of the leaves united. The leaves or fronds when young are rolled up like a crozier, and are covered with scales or chaff. The leaves or fronds are divided like compound leaves, and have on their back minute rounded clusters of fructification with a thin covering. These clusters consist of numerous little cases or bags partly surrounded by elastic rings, by means of which the sacs split transversely, so as to scatter the germs or spores, which are commonly called the dust of the fern. (Fig. 24, p. 226.)
2. Moss.--A common moss is apt to be neglected and overlooked ; but examine it and you see beautiful cellular leaves, a stalk bearing a brown urn-like case, covered often with a thin hood which falls off ; at the upper part of the urn-case is a lid which usually falls off, in order to allow the germs to be scattered. After the lid is removed, there is seen round the upper part or mouth of the sac, a beautiful fringe consisting of cellular processes, which are arranged in fours, or in multiples of four, as 8, 12, 16, 32, &c. The beautiful structure of a moss, as well as of other cryptogamic plants, which require the aid of the microscope for their examination, is well fitted to call forth our wonder and our admiration of the works of that Being who, while he weighs the hills in scales and the mountains in a balance, despises not the minutest organism in creation.
CLASSIFICATION OR ARRANGEMENT OF PLANTS.
When we examine the vegetable kingdom we find throughout the whole of it not only a beautiful principle of adaptation, indicating the work and superintendence of a designing mind; but also a system of order and arrangement, both as regards the parts of which plants are composed, and the relation which the members of the vegetable kingdom bear to each other.
We see around us various kinds of plants which more or less resemble each other, or, in other words, which are more or less related to each other. In botanical classification we endeavour to mark these resemblances, to determine their relation, and to trace out the plan on which they have been arranged by the great Author of Nature. We must aid the student of botany in his researches by adopting some classification of the 120,000 known species of plants on the earth. Two systems of classification have been adopted. One of them is called artificial, because it selects arbitrarily only one or two characters, and endeavours to group all plants according to them. The other is called natural, because it attempts to group plants by means of all their important characters, and takes into account their affinity and relation in all essential points. To the former is referred the system of Linnæus, which divides plants into classes and orders by means of the stamens and pistils. Such a system does sometimes bring together plants which are evidently nearly allied, but it often separates them. It resembles an alphabetical index, where all that requires to be known is the succession of the letters of the alphabet, and where subjects are placed together which are often totally distinct.
The natural method, on the other hand, brings in the idea of affinity or alliance in all important characters, and it professes to group together plants which are truly related in essential parts. It is like a well-arranged analytical table of contents, in which allied subjects are brought together, and the whole is arranged so as to give a complete idea of the plan in the mind of the author.
* The lesson under this head is chiefly taken from Professor Balfour's work on Religion and Botany. A. & C. Black, Edinburgh, 1859.