William S. Furneaux

Although several of the flowers mentioned in the last chapter as blooming during the present season may be seen along the borders of woods, yet within the wood itself we are struck by the almost total absence of flowers. This loss, however, is compensated for by the beautiful and varied tints assumed by the leaves of the trees and shrubs.

Important changes are now taking place in these perennial members of the vegetable world in preparation for the coming winter. The temperature of the soil is becoming considerably reduced, and, as a result, the absorbing activity of the roots is greatly decreased, while the winter is coming, when the temperature will be so low at times that the circulation of the sap will practically cease. If the leaves remained on the trees, they would give off from their surfaces more water than the trees could obtain from the soil through their inactive roots, thus endangering the lives of the trees. The leaves, therefore, must be shed. But these leaves contain a considerable amount of nutritious material which they themselves have built up, and which should not be lost. They contain starch, albumen, and other compounds which would be entirely lost to the trees if the leaves were shed in their present condition, except that a small proportion, in the form of products of decomposition, might be re-absorbed.

This being the case, arrangements must be made, first, for the passage of the nutritious material in the leaves to some other part of the tree where it can be stored for the winter; and, second, for the removal of the leaves as the roots become less active.

So, before the time of leaf-fall, the nutritious substances in the leaves, including the chlorophyll to which the leaf owes its green colour, become changed, and pass back to the stems or the root, where they can be safely stored for the winter. The leaves, thus impoverished, become mere skeletons—mere collections of empty, lifeless cells; and if no further change takes place, they assume a very pale colour, like the leaves of the Hornbeam, Birch, and the Willows.

But the transfer of the nutrient matter from leaf to stem or root is accompanied by numerous chemical changes by which new compounds are formed. Among these new substances a dark blue compound called anthocyanin is produced in some plants; and where this exists in considerable quantities we find the leaves of a dark bluish-green colour, like that of the autumn foliage of the Pine.

Acids are also sometimes formed as a result of the complicated chemical changes that take place during the transfer above described; and these react on the anthocyanin present, changing its colour to a tint that varies according to the proportion and quantity in which they exist.

Thus, if anthocyanin is present, together with a small amount of acid, the leaves are turned violet, as in the case of the autumn leaves of the Dogwood and the Spindle Tree; or purple, like those of the Service Tree. A larger proportion of acid produces, with the anthocyanin, the brownish green tint of the Alder leaves; or the brownish yellow of the Oak; while still larger proportions will turn the anthocyanin yellow, orange, red, or scarlet, according to the quantity in which the latter is present. Thus we can account for the rich yellow of the Maple in autumn, the orange of the Aspen leaves, the beautiful scarlet tints of the Mountain Ash and the Barberry, and the grand display of varied colours exhibited by the autumn Beeches.

Again, before the leaves are shed, the buds that are destined to produce the new branches of the following spring are already formed. These may be seen on all deciduous trees and shrubs, some of them in the axils of the leaves, and others at the tips of the present twigs. Each bud is the embryo branch of the following year. Some of them are destined to produce leafy branches only; some are to develop into branches bearing both floral leaves and flowers; while others are to produce flowers without floral leaves; and it is interesting to note that, even at this stage, sections of the buds, examined with the aid of a microscope, will reveal the future leaves and flowers compactly concealed within their scaly, protective coverings.

In October we may see the well-formed catkins of the Birch that are to bloom in the following April, in company with the ripe fruiting catkins of the present year. The Alder also bears its catkins that are to flower five months later, together with the woody remains of the female catkins of the previous spring; and the Hazel may be seen with its ripe nuts and its future flowers both on the same twig.

The Alder in Autumn, with the Catkins Which Mature in the Following Spring.

The leaves, having manufactured the materials necessary for the formation of the buds that are to produce the leaves and flowers of the following year, and then transferred their remaining store of nutrient matter to a suitable storehouse for the winter, are now practically empty and lifeless. Had they remained alive and active, they would have endangered the life of the tree by giving off more moisture than could be replaced by the inactive roots. In their present, lifeless condition they are useless to the tree; but by falling to the ground, and decomposing where they lie, they improve the soil by the addition of organic matter as well as of the mineral salts they contained.

In countries where a moderate temperature is maintained throughout the year, the growth of plants and trees goes on without interruption, and the fall of the leaf is hardly noticeable; for the older leaves die and fall one by one, as they become incapable of performing their functions for want of light, and new ones are being continuously formed close to the tips of the twigs. But where the growth is interrupted, either in hot countries during periods of drought, or in temperate countries by the approach of a cold season, the whole of the foliage is shed within a short period, and new leaves as suddenly appear when favourable conditions return.

In our own latitudes, as we all know, the defoliation of the trees is caused by the approach of cold weather, which decreases the activity of the roots, so that the leaves become dry and lifeless. It is very commonly supposed that the fall of the leaf is caused by frost; but this is not the case. The leaves are shed during the cool days of autumn, even though the temperature does not fall to freezing point; but it is equally certain that the leaf-fall is accelerated by the frost when it comes, for the little moisture remaining in the leaves is then frozen, rendering the structures so brittle that they are easily snapped by the wind.

The real cause of the rupture of the leaf is the formation of what is called the 'separation layer.' This consists of soft, succulent cells, really in several layers, which are formed across the leaf-stalk, usually at the base, where the bundles of vessels passing from the twig to the leaf are narrower. The walls of these cells are thin, and are easily separated; and as they extend inwards from the surface all round, they break through the old cells, thus weakening the junction. When the growth of the separation layer is complete, it requires very little force to break off the leaf, and the process is aided by the formation of certain organic acids which act on the cell-walls, causing them to dissolve; and when the leaf has finally separated from the twig, it will be found that the scar left is a clean-cut surface, such as would be produced by the incision of a sharp knife.

The recognition of the above facts introduces to us a difficulty for which we can find no explanation:—If the leaf-fall is not caused by frost, but by certain structural alterations that take place in the tree itself, how are we to account for the fact that the tree produces the changes which are necessary for its own preservation every year, just at the proper season? Plants and trees do not foresee the coming period of cold weather that necessitates the performance of the functions which they execute, and yet they instinctively prepare for the winter in the manner described above.

Our autumn observations teach us that there are interesting differences in the times and progress of leaf-fall of different species of trees, and also of trees of the same species when exposed to different external conditions. On open ground, where the trees are fully exposed both to the sun's rays and to the cool autumn breezes, the leaves lose their moisture and fall earlier than would the same species in more sheltered situations; and they retain their moisture and position latest in damp, shady woods. On high hills, where the exposure is extreme, the leaves, which, by the way, do not appear till late in the spring, fall early on account of the low temperature, and consequent decrease of root activity, in the autumn.

Further, we note that while in some trees, such as the Ash, Hornbeam, Beech and Hazel, the leaves fall first at the tips of the branches, and the defoliation extends fairly regularly towards the trunk, in other species, including Willows, Poplars, and the Lime, the branches become bare first at their bases, and finally at their tips.

Even during the depths of winter we may see a number of dead leaves still attached to the twigs of certain trees, notably the Oak and the Beech; but where we find practically all the foliage remaining on the tree or on special branches of a tree, we may generally assume that the tree, or the branches in question, are dead—that they died during the summer, before the separation layers of the leaves had been formed. We can also understand, from what has been said, why the dead leaves remain attached to a cut branch, and yet fall from the living tree from which it was severed.

In our own country some plants and trees retain their leaves throughout the year, so that we speak of them as evergreens. Many of these include herbaceous plants of a hardy nature, some of which remain fresh and green even in exposed situations, while others grow in more sheltered places. In either case they are plants whose roots remain more or less active in the cold season; and some of them, especially the evergreen shrubs, have rather thick leaves which contain a considerable quantity of sap, and which are surrounded by an outer covering or epidermis that does not allow the water within to pass out so readily as in the case of the deciduous leaves.

In addition to the observations previously mentioned, we should do well, at this season of the year, to study the autumn fruits of our trees and shrubs, most of which still remain attached to the twigs.

Some of these fruits lose most of their moisture as they ripen, thus becoming very light, and are provided with wings that cause them to be dispersed more or less by the wind.

The so-called 'keys' of the Ash are one-seeded fruits, extended at the end into a long, narrow wing with a slight twist. As a result of this peculiarity they usually fall less rapidly to the ground, spinning as they descend, and are thus carried farther than they otherwise would be by the wind. The fruits of the Sycamore and the Maple are somewhat similarly winged, and each of these consist of two carpels which separate sooner or later—generally after they have reached the ground.

On the Birch trees we may now see the ripe female catkins, consisting of hundreds of minute fruits, closely packed together, each provided with a wing on either side. They are very light, and easily blown a considerable distance by the wind; and late in the autumn we may observe the stalks of the catkins, from which some of the fruits have been blown, still on the trees.

The wings that thus aid in the dispersion of fruits are not always part of the fruit itself. In the Hornbeam it is a three-lobed, persistent bract that performs this function; and the fruits of the Lime are also blown away by the aid of a large bract from the middle of which the fruit-stalk projects.

Some of our trees present a glorious aspect during the autumn months, displaying conspicuous and more or less brightly-coloured fruits in combination with the varied autumn tints of their leaves. The red foliage of the Mountain Ash or Rowan is accompanied by the still brighter clusters of scarlet fruits—little apple-like pomes, about the size of holly 'berries'; and the Wayfaring Tree bears pretty clusters of flattened, oval, one-seeded berries which are first red, and then nearly black. The Guelder Rose, while still in full leaf, is often very heavily laden with its bright red, semi-transparent berries; and the violet foliage of the Dogwood is intermingled with clusters of little berry-like drupes which, at first green, have now changed to a rich purple-black. Then there is the Spindle Tree, with its pretty red lobed capsules which split, when ripe, at its angles, disclosing as many cells as there are lobes (usually four), each with a single seed enclosed in an orange jacket. Occasionally we meet with the Strawberry Tree, during early autumn, bearing both flower and fruit at the same time. This tree flowers in September and October, but the fruits which accompany the flowers are those of the previous year, for they require more than twelve months to come to maturity. The fruit is a large berry, of an orange-red colour, with a granulated surface that gives it somewhat the appearance of the strawberry. It should be mentioned that the Strawberry Tree is not indigenous to England, and is seldom seen outside parks and gardens; but it grows wild in Ireland, and is very abundant round Killarney and in other parts.

In conclusion, we must note one autumn flower of the woods which is exceedingly common—that of the Ivy (Hedera Helix), belonging to the order AraliaceÆ. The Ivy is an evergreen climber, fixing itself by means of little rootlike suckers attached to the main stem and its branches, while the lower branches trail along the ground. The leaves are thick and glossy, usually of a deep green colour, but often beautifully variegated. Those attached to the trailing and climbing stems have three or five lobes, are always turned with one surface towards the light, and are so arranged as to obtain the maximum of light, the less exposed leaves below catching the rays which pass between the lobes of those which are more favourably situated.

The branches of the tree do not, as a rule, produce flowers as long as they are able to climb; but as soon as they reach the summit of the tree or wall to which they cling, or reach a situation where there is a sufficient abundance of light and air, they change their character in a remarkable way. They now become bushy, cease to produce suckers, and give rise to undivided leaves that turn in all directions for light and air. At the tip of each twig is formed a cluster of yellowish-green flowers, arranged in a short raceme or in an umbel. These flowers have an inconspicuous calyx which forms a border round the middle of the ovary, and five short petals. There are also five stamens, and united styles. The fruit is a smooth, black berry, containing from two to five seeds.