Part 24

The Rue-leaved or Three-fingered Saxifrage (_S. tridactylites_) is a small species, rarely exceeding four or five inches in height, common on walls in most parts of Britain, flowering from April to July. The whole plant is usually more or less tinged with red, and its erect stem is covered with fine glandular hairs. The radical leaves are very small, stalked, and undivided; those of the upper part of the stem are also small and entire, but sessile; and the intermediate leaves, lower on the stem, are palmately divided into three or five narrow segments. The small white flowers are placed singly on rather long terminal and axillary stalks; and the hairy calyx, which adheres to the ovary, has five blunt lobes less than half the length of the petals.

Our last example of this order is the Cut-leaved or Mossy Saxifrage (_S. hypnoides_), a very variable plant, from three to ten inches high, rather rare in South England, but much more common in the rocky parts of North England and Scotland. It has numerous procumbent, barren stems with tufted leaves; and erect flowering stems bearing a few small leaves and a loose cyme of a few white flowers. Most of the leaves are narrow, pointed, entire, about a quarter of an inch long; but the larger ones, at the base of the plant, are about twice as long, and divided into three or five narrow lobes. The calyx adheres to the ovary to about two-thirds of the length of the latter, and has five lobes about one-third as long as the petals. This species flowers from May to July.

Old walls, ruins, and limestone cliffs are frequently adorned with the pretty flowers of the Snapdragon (_Antirrhinum majus_--order _Scrophulariaceæ_) which bloom from July to September. The plant varies from one to two feet in height, is tufted and leafy at the base, and has erect stems which bear racemes of large flowers. The leaves are very narrow and entire; and the flowers, which are usually white, pink or crimson, are shortly stalked in the axils of the small upper leaves. The calyx is deeply divided into broad lobes very much shorter than the corolla; and the latter consists of a broad tube and two lips, the whole being over an inch in length. The mouth of the flower is closed by a projecting 'palate,' but is easily opened by pressing the flower at the sides between finger and thumb. There are four stamens on the corolla, two longer than the others; and the fruit is an unsymmetrical capsule that opens when ripe by a few holes near the top.

The Ivy-leaved Toadflax or Mother of Thousands (_Linaria Cymbalaria_), of the same order, is a pretty little trailing plant very commonly seen on old walls in many parts of Britain, particularly in the South-West. It will grow luxuriantly in places where there is no soil other than that afforded by the crumbling mortar, and will often establish itself even on new walls so compactly built that it is difficult to see how the plant can find the necessary moisture or how its roots can penetrate the hard material to which it is attached. Its slender stems vary from a few inches to two feet in length, often rooting at the nodes; and its little leaves are smooth, with three or five lobes, and generally of a purplish colour on the under side. The little flowers, which bloom from May to September, are of a pale blue or lilac colour. The lipped corolla is very similar to that of the last species, with a yellowish palate closing the mouth, but it has a short spur at the base.

The one remaining flower of this chapter is the Wall Pellitory (_Parietaria officinalis_), which belongs to the Nettle family (_Urticaceæ_). It is a somewhat bushy plant, varying from six inches to two feet in height, bearing axillary clusters of small, sessile, green flowers from June to September, and is common on walls and stony banks, more especially in the South of England. Most of the flowers are usually imperfect, and the clusters are surrounded by a whorl of a few divided bracts. The males are few in number, each consisting of a hairy perianth, and four stamens which are jointed and very elastic, springing suddenly and shedding their pollen when touched; the females have a tubular, hairy perianth of four lobes, and a single tufted stigma.

XXI

FIELD AND WAYSIDE IN AUTUMN

From the end of September onward the number of wild flowers is rapidly decreasing, but still there is much to be seen that will be interesting to the observant student of Nature. Many of the summer flowers are quite over, while others continue to bloom till, at last, they succumb to the intensifying frosts; but hundreds of species of the summer-flowering plants are now in fruit, and some of these are almost as interesting in this stage as when in flower. Many plants will have been observed in flower before any of their fruits were fully formed, but autumn is the season when a large number of these may be seen in full fruit, and watched as they make arrangements for the dispersal of their seeds.

We have already given (p. 12) an outline classification of the various kinds of fruits, and if the reader will study this during the autumn months, and examine the field and woodland plants that fall in his way, he will find abundance of work awaiting him on every country ramble.

A large number of wind-dispersed fruits and seeds are ripe long before the autumn sets in, and have already been distributed by the summer breezes; but now, with fewer flowers to attract attention, one can give more time to the observations of the movements of tufted and winged seeds and fruits as they sail through the air. And, as we brush by the hedgerows and the borders of fields in search of various flowers and fruits, we soon become acquainted with a variety of bristled, hooked, and barbed fruits that are effectually dispersed by the agency of animals, quite a large number of these having securely fastened themselves to our clothing.

Many fruits remain attached to their plants long after the last flowers, and even the leaves, have entirely disappeared. Some of these await the gales of late autumn and winter, and being now no longer sheltered from the wind, are carried to the spots where they are to produce new plants in the following spring; while sheep and other animals, wandering farther afield in search of food, carry away numerous hooked fruits in their woolly or hairy coats.

The feathered fruits of the Wild Clematis adorn the hedgerows throughout the greater part of the cold season, and form a striking feature of the wayside until they have been dispersed by the winter storms; and the hips of the Wild Rose, as well as the berries and drupes of various shrubs, now rendered more conspicuous by their bright colouring and the absence of foliage, are devoured by birds which afterwards deposit the indigestible and, therefore, uninjured seeds, with their excrement, at some distant spot.

Should the reader be interested in the various ways in which the dehiscent fruits discharge their seeds, he will do well to collect a number of species, as yet unopened, and expose them to the sun in a dry place. He will then be able to note not only the directions and extent of the dehiscence, but also to observe the forcible ejection of seeds by those which split elastically, or which, by other mechanical contrivances, have the power of throwing their seeds a considerable distance.

We may find still another subject for study in the beautiful autumn tints assumed by the leaves of many plants. Such tints are, of course, most conspicuous in the foliage of our forest trees and shrubs; and, when speaking of these, we shall have a word or two to say with regard to the nature of the internal changes that give rise to the beautiful display of colours; but not a few of the hedgerow herbs and shrubs exhibit tints equally rich and varied. Note, for instance, the pretty Herb Robert, still in flower in sheltered places, its blossoms standing out beyond a background of richly-coloured leaves.

The vigorous summer growth of flowery banks and hedgerows is often closely trimmed with the sickle for the greater convenience of pedestrians and vehicular traffic, all the flowers and overhanging twigs being closely cut, and the wayside thus destroyed from the Nature-student's point of view; but the ground so denuded has recovered itself by the autumn, and a second crop of flowers, arising from the old stocks, often later than their normal season, is frequently the result.

A considerable number of summer flowers continue to bloom during the autumn months, while a few are truly autumnal, and are not to be found till the summer has nearly or quite passed.

In corn-fields we may still meet with the beautiful Pheasant's-eye (_Adonis autumnalis_), and in fields the Hairy Buttercup (_Ranunculus hirsutus_), the Daisy (_Bellis perennis_) and the Red Hemp-nettle (_Galeopsis Ladanum_) are yet in flower, while the Annual Meadow Grass (_Poa annua_) continues to produce new flowers to the end of the year.

On sunny banks in chalk districts we still see the delicate Rock Rose (_Helianthemum vulgare_); and on banks almost everywhere the Wild Clary (_Salvia Verbenaca_), and the still more hardy Milfoil (_Achillea millefolium_), Knapweeds (_Centaurea nigra_ and _C. Scabiosa_), Field Scabious (_Knautia arvensis_), Dark Mullein (_Verbascum nigrum_) and the Toadflax (_Linaria vulgaris_).

Then, on downs and heaths we find the Yellow Bedstraw (_Galium verum_), the crimson flowers of the Fine-leaved Heath (_Erica cinerea_), and the rose-coloured or white blossoms of the Heather or Ling (_Calluna vulgaris_): also the Carline Thistle (_Carlina vulgaris_), with its inner involucral bracts broadly spreading while the sun shines, but bent inwards to protect the florets during dull weather when the insects are at rest, the lilac flower-heads of the Devil's-bit Scabious (_Scabiosa succisa_) and the Small Scabious (_S. Columbaria_), and the conspicuous flowers of the Chamomile (_Anthemis nobilis_), all standing out in bold relief against the background of autumnal foliage.

Still more numerous are the autumn flowers of the waysides. By the dry and dusty roadside we see the yellow flowers and silvery leaves of the Silver-weed (_Potentilla anserina_), the little starlike flowers of the Chickweed (_Stellaria media_), the yellow flower-heads of the Dandelion (_Taraxacum officinale_), Sow Thistle (_Sonchus oleraceus_) and Groundsel (_Senecio vulgaris_), the straggling Knot-grass (_Polygonum aviculare_), the Spotted Persicary (_Polygonum Persicaria_), the Shepherd's Purse (_Capsella Bursa-pastoris_), the Scentless Mayweed (_Matricaria inodora_), the Chamomile (_Anthemis nobilis_), the White Goose-foot (_Chenopodium album_), and Oraches (_Atriplex hastata_ and _A. patula_). Where the soil is more generous we find the Herb Robert (_Geranium Robertianum_), the Fleabane (_Inula dysenterica_), Red and White Dead-nettles (_Lamium purpureum_ and _L. album_), and the Petty Spurge (_Euphorbia Peplus_); while on old walls the Pellitory (_Parietaria officinalis_) is still in flower.

XXII

AUTUMN IN THE WOODS

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 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.