Flowering plants are composed of four distinct sets of organs, to each of which is assigned a particular role in the life of the whole. (1) The Root serves to fix the plant firmly in the soil, and to absorb from the soil the water and the mineral salts 9 which the plant requires. (2) The Stem bears the leaves and flowers, holds them in advantageous positions, and carries to them water and various nutrient material. (3) The Leaves receive from the root water and mineral substances, and from the air the important gas Carbon dioxide; from these they are able to build up the food of the plant - such substances as sugar and starch. This they do by virtue of their green colouring-matter, which absorbs a large quantity of light, necessary for the carrying on of the chemical processes involved in the formation of the food substances. (4) The Flowers have as their special function the reproduction of the plant by means of seed-formation. In reality the flower is a collection of leaves, deeply modified to enable them to perform their new work; some produce the true reproductive bodies - the pollen-grains and the ovules - others protect these, and aid them in various ways.

For our present purpose it is necessary to consider the external form only of these different parts: a fuller treatment of their structure, and of the way in which they carry on their work, is to be found in another of the books of this series, Dr. Marie Stopes' Modern Botany.

1. The Root. - Only in comparatively few cases does the root present features of value for the identification of a plant; of interest are those roots, which serve to store food, and so become swollen and tuberous {e.g. orchis).

2. The Stem. - It may be necessary to note whether the stem is branched or without branches - simple. Many stems stand straight up - erect; but frequently we meet with plants the stems of which lie along the ground - prostrate/ in yet other cases the stem may support itself on external objects - climb or ramble.

3. The Leaf is typically divided into two parts, the leaf-stalk and the blade; very often, however, there is no stalk, and then the leaf is said to be sessile. The margin of the blade is sometimes quite smooth - entire - but usually it is cut into or notched in various ways. If it presents a series of little teeth pointing forwards, like those of a saw, it is serrate/ if the teeth are more irregular and point outwards, it is toothed. Often the cutting is much more profound; it may go right down to the central vein (mid-rib) of the leaf, so dividing it into a number of smaller leaflets, in which case we have a compound leaf as opposed to a simple leaf - one in which the cutting does not reach the mid-rib. If the cutting, though not deep enough to form a compound leaf, yet divides it very deeply, we have a segmented leaf; if the cutting is less marked still, the leaf is said to be lobed. In compound, segmented, and lobed leaves the cutting may take place in two different ways: (1) if the leaflets, segments, or lobes radiate out from one point at the apex of the leaf-stalk, the leaf is palm-compound (segmented, etc.); (2) if, on the contrary, they arise at the sides of the midrib, it is feather-compound, etc. Often the leaflets of a compound leaf are themselves compound, in which case the leaf is doubly compound: further complications are adequately described by combinations of the terms given above.

The actual shape of the leaf or leaflets is described by a series of terms, some of which are self-explanatory, while the meaning of the others may be best understood by reference to the accompanying diagrams. One term requires special mention; by lyre-shaped, we mean a feather-compound or feather-lobed leaf, in which the terminal lobe or leaflet is larger than the others.

Ovate leaf with toothed margins.

Fig. 1.

Heart shaped leaf with serrate margins

Fig. 2.

Lance shaped leaf.

Fig. 3.

Elliptical leaf.

Fig. 4.

Arrow shaped leaf.

Fig. 5.

Halbert shaped leaf.

Fig. 6

Feather compound leaf with seven leaflets and two stipules (st.).

Fig. 7.

Palm lobed leaf.

Fig. 8.

Feather segmented leaf, lyre shaped, with coarsely toothed margins

Fig. 9.

Fig. 1. - Ovate leaf with toothed margins. Fig. 2. - Heart-shaped leaf with serrate margins. Fig. 3. - Lance-shaped leaf. Fig. 4. - Elliptical leaf. Fig. 5. - Arrow-shaped leaf. Fig. 6. - Halbert-shaped leaf. Fig. 7. - Feather-compound leaf with seven leaflets and two stipules (st.). Fig. 8. - Palm-lobed leaf. Fig. 9. - Feather-segmented leaf, lyre-shaped, with coarsely toothed margins.

In many plants there are to be found, at the base of the leaf-stalk, two leafy outgrowths, sometimes quite small, sometimes as large as the leaf itself - these are called stipules.

Of the surface of the leaf, we note that it may be smooth or hairy; and of its texture that, in a few cases, it is fleshy or leathery.

4. The Flower. - If we pull the flower of a buttercup to pieces, we find that it consists of four different kinds of organs. To the outside there is a whorl (or circle) of five greenish scales: these are sepals, and together make up the calyx, which in the bud protects the delicate internal parts of the flower. Then comes a whorl of yellow petals, forming the corolla: its bright colour, and the fact that frequently, as in this case, there is to be found honey about its base, induce insects to visit the flower. Inside the corolla there is a large number of stamens; each of these consists of a delicate stalk, and a little head, in which is produced the dust-like pollen. Finally, in the centre is a number of green grains, the seed-vessels: at the tip of the seed-vessel is a receptive spot - the stigma - which is frequently borne on a slender stalk - the style. Before the flower can set seed, it is necessary for the ovules, which are contained in the seed-vessel, to be fertilised, and this can take place only if pollen from the stamens reaches the stigma - the receptive spot of the seed-vessel. It has been found that better and more abundant seed is set if the pollen be obtained from the flower of another plant, and it is for the purpose of attaining this end that the plant invites the visits of insects. These, in their hunt for honey, brush against the stamens and stigma, and as they always carry about a dust of foreign pollen, there is a considerable chance that the stigma of a flower will receive pollen from one of its kind, growing on a separate plant.

The different parts of the flower may be arranged in different ways: frequently a complete set of parts is wanting - the wood anemone, for example, has no corolla, but only a calyx, which has become brightly coloured to take the place of the missing petals. If either stamens, or seed-vessel, be absent, then two kinds of flowers, one male with stamens, one female with seed-vessels, are found, and sometimes on different plants. The numbers of the parts vary greatly. Frequently the parts of a whorl are united to form a single piece. The seed-vessel is often embedded in the flower-stalk, below the other parts, instead of being above them, as in the buttercup.

The flowers may occur singly in the axils of the leaves, that is, in the angle between the leaf and the stem; but more frequently they are grouped in characteristic inflorescences. By a spike we mean, in this book, any elongated mass of flowers occupying the apex of a stem or branch. By an umbel we mean an inflorescence in which the stem or branch ends abruptly, giving rise to a large number of flower-stalks, the lengths of which are such that the flowers all occupy one level, and so form a flat, pancake-like, or convex, umbrella-like group (e.g. Figs. 6, 7). By a composite head we mean a close head of flowers surrounded by a number of greenish scales or leaves the daisy shows this type. If we examine the so-called flower of the daisy, we find that it is made up of a great number of little flowers - those to the centre with a tubular, yellow corolla, stamens, and a seed-vessel; those to the margin with a white, strap-shaped corolla, and a seed-vessel: while outside is a large number of green scales; these serve to distinguish this type from the simple head of a clover, which does not possess them. The centre part of the daisy flower-head is spoken of as the disc, the marginal part as the ray.