Part 26

It is not sufficient that we are able to recognise trees when in leaf; they should be known equally or almost as well during the winter and early spring while the branches are bare, and this is usually easily accomplished by making ourselves acquainted with the general form of each tree as viewed from a distance, and, on closer inspection, with the nature of the bark and the character of the buds.

All our forest trees are of the exogenous type; that is, their stems increase in thickness by the addition of new wood formed outside the older wood and underneath the bark. Thus the bark, which is composed of a layer or mass of dead, sapless cells, is gradually pushed outward as the stem thickens. The result is that the bark is either more or less fractured, as in the Elm and the Oak, or it flakes off and falls to the ground, as is the case with the Plane and the Birch. A new layer of bark is always formed during each summer, and this, in turn, either cracks or peels away; but while, in the former instance, the accumulated bark presents a very rugged appearance, and becomes very thick, in the latter case it remains smooth, and is always thin.

Then again, how are we to account for the great variety in the general forms of our different trees--the irregular, crooked nature of the Oak; the slender, but denser branching of the airy Birch; and the tall, pyramidal form of the Lombardy Poplar? All this is easily understood if we carefully observe the positions of the buds as seen during the winter months; and watch the development of these buds during early spring.

If the buds are irregularly scattered on the twigs, the lateral buds being as strongly developed as the terminal ones, while, in the spring, as is often the case, certain only of the buds develop into new twigs, the others remaining dormant, then the branches assume that irregular, crooked appearance so characteristic of the Oak. If, on the other hand, all the terminal buds are well developed, and the lateral buds are weaker and more regularly distributed, but farther apart, then the tree grows more rapidly in height than in breadth, and assumes more nearly the character of the Pyramidal Poplar. It will thus be seen that the study of trees in their winter condition is not altogether lacking in interest.

Referring once more, but briefly, to the matter of dormant buds, we recommend the reader not only to observe that some buds do not expand with the others during the spring, but to make them the subject of experiment. Thus, when the Horsechestnut is well in leaf, dormant buds will usually be seen on the sides of the twigs, sheltered by the spreading leaves produced at the tips. Now remove the whole cluster of leaves formed by the terminal bud, together with the bud itself, and the hitherto dormant laterals, under the influence of increased light and warmth, and supplied with sap that is now directed into new channels, will speedily show signs of growth. Similarly, the fruit-gardener will remove the tips of the branches of his fruit trees, which often bear buds that are destined to produce leafy twigs only, and thus encourage the growth of the fruiting buds that are situated lower on the twigs.

Let us now briefly consider the structure of buds and the manner in which they are protected. Most buds are surrounded by brownish scales which are impervious to water, and thus prevent a loss by evaporation at a season when the activity of the roots in absorbing moisture from the soil is suspended. Such loss is still further insured in some cases by a covering of natural varnish. On removing this protective coat we find a dense cluster of closely-packed leaves, variously folded or crumpled in different species, and often, in the centre, a cluster of flowers.

What, then, is the true definition of a bud? It is a young branch, and may give rise to a mature branch bearing foliage leaves only, floral leaves only, or a combination of both. A transverse section of a bud, examined, if necessary, with the aid of the microscope, will show the nature of the branch it was destined to produce; and, in the case of buds which represent, in embryo, branches bearing flowers, or both leaves and flowers, it is often an easy matter to see the whorls of the future flowers, and even the pollen cells in the anthers and the ovules in the ovary.

Interesting as it is to study the structure of buds in their dormant condition during winter and early spring, even more fascinating is the watching of the gradual expansion of the bud and the unfolding of the young leaves. And it is not always necessary to make frequent visits to the woods in order to carry out such observations, for a large number of buds will develop almost equally well, at any rate through their earlier stages, if the twigs bearing them be placed in vessels of water either in or out of doors; and in many cases all the stages from dormant bud to perfect leaves and fully-expanded flowers may be watched in this way.

We have spoken of the protection afforded to the dormant bud during the winter period, but it is interesting to note that protection is necessary for the young leaves even after they have forced themselves well out into the light and air. The reason for this is that the epidermis or outer skin of the young leaf is not properly developed. It is not yet water-tight, and, consequently, the sap of the tender leaves would rapidly evaporate, so that they would soon become dry and shrivelled.

The means by which the young leaves are protected will be readily seen if we watch the gradual development of the bud. In many cases these leaves remain folded long after they have left the shelter of the original bud-scales, the manner of folding being the same as that which obtained while within the bud. Sometimes they are folded like a fan, or like the leaves of a book; sometimes rolled one within the other, or irregularly crumpled in such a manner that nothing is exposed to the air except the edges of the leaves and the surfaces of the veins.

In addition to the protection from evaporation afforded by the folding of the young leaves, many are covered with a dense coat of "wool." Young leaves of the Horsechestnut are very thickly covered with such a coat, of which only the slightest traces are to be seen in the fully-grown leaf. The young leaves of the Beech are folded like a fan for some time after they have left the enclosure of the bud, and the folding is such that the only parts exposed are the margins, the midrib, and the strongly-marked parallel veins. But since all these parts are provided with hairs, the young leaf, as long as it is folded, is surrounded by a complete protective covering. As the epidermis develops, and the danger of loss by evaporation thus reduced, the leaf straightens itself out, and the hairs either fall or become shrivelled. The leaf of the Wayfaring Tree is protected, while young, by a complete covering of starlike hairs which form a fine felted coat over the whole surface; and when the epidermis is properly formed, the hairs are all shed.

Some young leaves are preserved by scaly stipules which surround them after they have emerged from the bud; and as soon as the epidermis is sufficiently impermeable the stipules, having done their work, fall to the ground. So great is the shower of these transient structures, in the case of the Oak, Elm, and Lime trees, that the ground is almost completely covered by them.

Young leaves have yet another way of preventing the evaporation of their sap, and that is by turning themselves into the erect position so that the warmth of the spring sun has but little effect on them. The young leaves of various grasses turn their apices upwards; while those of the Horsechestnut, after having lost the protection afforded by the woolly covering and the original folding, turn themselves with their points downwards. Later, when the epidermis is well formed, and the leaves are so far developed that they are capable of utilising the energy of the sun in the performance of their functions, they take up the horizontal position.

Another interesting matter for spring observation is the relative times of the bursting of the flowering buds and the leafing buds on the same species of tree or shrub. In many cases the former are fully developed before the latter show any signs of active growth, or while the foliage is as yet only passing through its earliest stages. The Hazel catkins shed their abundance of pollen before the foliage buds show the slightest signs of green. The Blackthorn is white with snowy blossoms before a leaf appears. The upper twigs of the Elm appear fluffy in the distance through the formation of its flowers while the foliage buds are still dormant; and the Alder, Willow, Poplar and Aspen likewise produce full-blown catkins while their branches are otherwise bare. Of the trees above named, the Hazel, Elm, Alder, Poplar, and Aspen are dependent on the spring winds for the transfer of the pollen, but the pollination of the Willow and the Blackthorn is brought about by the agency of early insects which visit the flowers for the nectar they provide.

The same spring sun which calls forth the new leaves and early flowers exerts its vivifying influence on the seeds that fell to the ground before the winter's frosts set in, and in sheltered places myriads of young seedlings of plants and trees may be found in their first stages of growth. The early history of a plant is as interesting a study as that of the mature specimen, and the young botanist will do well if he seeks out the germinating seeds and watches their development. This part of botanical study may, perhaps, be carried on more conveniently at home than in the field, for the seedlings may be grown in soil, wet sawdust, or in water alone, and the stages closely observed.

The seed is a plant in embryo. It consists of a young root, a bud, and one or two seed-leaves or cotyledons. Some seeds contain nothing but the parts just named, and when this is the case the cotyledons contain a reserve of food material sufficient to maintain the developing plant until the root is enabled to absorb sufficient nutriment from the soil, and the first foliage leaves are so far advanced that they can absorb carbonic acid gas from the air, and build up with the aid of this gas, together with the food obtained from the soil, the compounds required by the growing plant.

Other seeds contain, in addition to the embryo, a reserve of nutrient material quite distinct from it; and in such instances the cotyledons have the power of taking up this reserve, changing it to a condition suitable to the requirements of the plant, and then distributing it to the growing parts.

In some seedlings the cotyledons will remain for some time within, or partially within the seed, in order that they may continue the absorption of this reserve; and while this process is going on the seed may remain below the surface of the soil, or it may be lifted into the air by the upward growth of the cotyledons themselves.

In cases where the cotyledons contain the food reserve for the seedling they sometimes remain under the soil, but in many instances they are pushed into the air by the upward growth of that portion of the plant axis immediately below them. In either case they decay as soon as their work is accomplished. This often happens as soon as they have delivered up to the seedling their reserve of food, but frequently the cotyledons which ascend into the air expand, becoming really leaflike in general appearance, assuming a green colour through the development of chlorophyll (the green colouring matter of plants), and then perform all the functions of the ordinary foliage leaves of the plant. Such cotyledons often continue to exist long after the first foliage leaves have appeared from the bud, for, although the original food reserve has been exhausted, they are now in a position to manufacture, under the combined influence of the sun's warmth and light, compounds essential for their own growth as well as that of the other parts of the seedling. These cotyledons, however, are never of the same form as the true foliage leaves.

The student should obtain a variety of seeds or seedlings of our wild plants and forest trees in order to study these interesting early stages. Such employment will prove very valuable at a season when there is but little call for outdoor work.

WOODS AND THICKETS IN SPRING

One of our earliest spring flowers of the wood is the lovely Daffodil or Lent Lily (Narcissus Pseudo-narcissus) of the order Amaryllidaceæ. This plant develops from a bulb--an underground bud formed of thick, fleshy leaves; and the flowers appear during March and April. The perianth is composed of a tube and six spreading limbs of a delicate yellow colour; and a deep, bell-shaped, golden coronet, beautifully notched and curled at the rim.

During April and May we meet with the beautiful little Wood Anemone (Anemone nemorosa--order Ranunculaceæ), often in such abundance that the ground beneath the trees is completely covered by its graceful leaves and flowers. The leaves are radical, stalked, and deeply lobed, springing from an underground stem. On the flower stalk, some distance below the flower, is a whorl of stalked bracts of the same form as the radical leaves. The flower has six spreading sepals, resembling petals, usually white, but often tinged with a delicate pink, or, more rarely, with blue. The fruit consists of a number of downy achenes.

Belonging to the same order (Ranunculaceæ) we have two species of Hellebore--the Green Hellebore (Helleborus viridis) and the Stinking Hellebore (H. foetidus), both found in woods on chalk or limestone during April and May. The former, also known in parts as the Bear's-foot (Plate I, Fig. 1), has leaves palmately lobed, consisting of five or seven parts; and the flowers, which are more than an inch across, have spreading green sepals, and small tubular petals which contain nectar that is supposed to be poisonous on account of the small dead flies that are commonly found sticking to it. The Stinking Hellebore, or Setterwort, has evergreen, radical leaves, the lobes of which do not radiate from a common centre; and the flowers, of which there are many on each peduncle, have erect sepals.

The Goldilocks or Wood Ranunculus (Ranunculus auricomus) is a flower very much like the Upright Meadow Buttercup (p. 211), though not nearly so tall, being only from six to ten inches high. It grows chiefly in thickets and copses, and flowers from April to July. Its root is fibrous; the stem erect, slender, and branched; the radical leaves long-stalked, round or kidney-shaped, divided into three, five, or seven lobes; and the stem leaves few, sessile, and palmately divided to the base into very narrow segments. The calyx is downy, consisting of spreading, yellow sepals; and the petals are often partially or entirely wanting. This plant is widely distributed, but is most frequent in the centre and south of England.

The Columbine (Aquilegia vulgaris), also one of the Ranunculaceæ, so well known as a garden flower, grows wild in the thickets and copses of several parts, blooming from May to July. Its branched stem grows to a height of one or two feet; and the leaves are stalked, with three broad, stalked, three-lobed segments. The pretty, drooping flowers are usually over an inch in diameter, of a white, blue, or purple colour, in a loose, leafy panicle. They have five coloured, deciduous sepals; five petals, each with a curved spur that projects below the base of the calyx; numerous stamens; and an ovary of five carpels which ripen into as many follicles.

The Dog Violet (Viola canina--Order Violaceæ) is probably too well known to need description, seeing that it is easily distinguished from the other species of the same genus by the absence of scent and by the presence of running stems. It is, however, very variable, both in its habits and habitats, so much so, indeed, that some botanists regard the varieties as distinct species under the titles of Wood Violet, Dark Wood Violet, Pale Wood Violet, Hill Violet, Bog Violet, &c. These different forms are distinguished by the shape of the leaves, which may be broadly-cordate, narrow-cordate, or lanceolate; and also by the nature of the stem and the form and colour of the spur of the corolla. In some the main stem is flowerless, but flowering stems proceed from the axils of its leaves; in others the main stem is long and branched, bearing flowers. The narrow-leaved and branched varieties occur principally on heaths, while the broad-leaved forms, in which the main stem is flowerless, are found chiefly in woods. The student will do well to compare as many forms as possible as an interesting study in variation.

The flowers have five sepals; and five unequal petals, usually of a bluish-purple colour, the lower one prolonged backward into a blunt spur. Five stamens closely surround the ovary, which is composed of three carpels, but is one-celled.