Field and Woodland Plants. William S. Furneaux
of leaves. In fact, we often find that the size of the stipules is proportional to the number of tendrils produced; and that when the leaflets are considerably reduced in number by their conversion into tendrils, not only are the stipules large and leafy, but the stem itself may be extended laterally into broad wing-like expansions which do the work of foliage leaves.
Interesting illustrations of this are to be found in the Yellow Vetch—a rather rare plant sometimes seen in sandy fields—in which all the leaves are converted entirely into tendrils, and their function performed by very large leafy stipules; also in the Narrow-leaved Everlasting Pea of bushy places, in which the leaflets of the compound leaves are all converted into tendrils with the exception of two, the work of which is aided by the stipules and by the 'wings' of the stem and petioles. In the Rough-podded Vetch, too, the stems and petioles are winged to serve the same end; and other British members of this genus have either large stipules or winged stems, or both, to compensate for the loss of leaflets that have been modified into tendrils.
In other climbers the blade of the leaf is not reduced in size, even though the leaf serves the purpose of a tendril, the function of clinging being assigned exclusively to the petiole or leaf-stalk. This may be observed in the Wild Clematis and the Bryony, in both of which the petiole forms a ring round any branch or stem with which it comes in contact. These petioles are apparently equally sensitive on all sides, and are therefore ready to cling to any available support, whether above or below. In the Clematis the leaves are at first at right angles to the stem of the plant, but they afterwards turn downwards, and thus transform themselves into so many anchors which give additional aid in supporting the climber among the other hedgerow plants and shrubs.
IV
EARLY SPRING
The work of the botanist is light during the early spring, especially if his attention is directed only to plants and trees in their flowering stages; but, to one whose ambition is to study Nature in all her varied phases, this season of the bursting of the bud, when all things are awakening into new life, is full of interest, and demands no small amount of time.
The first flowers observed in the spring are mainly those hardy weeds which may be seen in bloom almost through the year, such as the Shepherd's Purse, Chickweed, Groundsel, White Dead Nettle, Red Dead Nettle, and Henbit Dead Nettle. These are soon followed by the Furze, Strawberry-leaved Cinquefoil, Snowdrop, Hazel, Common Whitlow-grass, and other flowers that are truly blossoms of the spring. All these will be described in turn, according to their various habitats; the object of the present short chapter being to note those signs of early spring which demand the attention of the lover of Nature while flowers are as yet few and inconspicuous.
A ramble over bleak downs and moors during the cold days of early spring will probably reveal but little of interest in the way of vegetable life, but in sheltered vales and woods, copses, and protected waysides, there is much to be observed. Here it is that we find the hardy weeds which have continued to bloom throughout the winter months; the earliest of the spring flowers; the fresh green foliage of herbs and shrubs that, in more exposed situations, have been completely denuded; the first tender seedlings appearing above the ground long before the frosts are over; and the expanding 'leaf-buds' showing their green while elsewhere all life seems dormant.
This is the season when the young botanist requires his notebook more than the collecting-book or vasculum; for his records of early flowers, and of the times of the appearance of the leaf in our trees and shrubs, will prove of great interest when compared with the corresponding events and times of other years. Not only do our spring seasons vary considerably from year to year in such a manner as to alter the general times of appearance of leaf and flower, but the vicissitudes of our climate even change the order in which these events occur.
The general study of the buds of trees should commence before they begin to burst. We commonly speak of the buds as winter buds, but it should be known that they were formed in the preceding summer or autumn, and have remained dormant throughout the winter. There is usually a terminal bud at the tip of each twig, and lateral buds at the sides. If we examine a lateral bud we find immediately beneath it a more or less distinct scar, denoting the position of a leaf that fell in the autumn, thus showing that the bud in question was formed in the axil or angle of the leaf. These observations should be verified by examining the trees in autumn, while the leaves still exist.
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.
Trees in Winter or Early Spring
1. Hazel, with catkins. 2. Ash. 3. Oak. 4. Lime, with remains of the last season's fruits.
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,