XXIFIELD AND WAYSIDE IN AUTUMN

The Wall Pellitory.

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—orderScrophulariaceæ) 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.

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.12an 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. Someof 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 bloomduring 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 nigraandC. 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 hastataandA. patula). Where the soil is more generous we find the Herb Robert (Geranium Robertianum), the Fleabane (Inula dysenterica), Red and White Dead-nettles (Lamium purpureumandL. album), and the Petty Spurge (Euphorbia Peplus); while on old walls the Pellitory (Parietaria officinalis) is still in flower.

Although several of the flowers mentioned in thelast chapteras 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 thechlorophyllto 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 thesoil 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 treeproduces 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 aresurrounded 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.

The Ash in Autumn, with its 'Keys.'

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, extendedat 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.

The Maple in Fruit.

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 notalways 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.

The Wayfaring Tree, in Fruit.

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 mentionedthat 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 orderAraliaceæ. 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 Strawberry Tree in Flower, with the Fruits (Almost Ripe) of the Previous Year.

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.

A number of plants extract more or less of the organic material they require from other plants, and thus save themselves the labour of building up this material themselves. These are termed parasites; but we must be careful to distinguish between them and certain other plants which, though apparently parasitic, are not really so. One plant may climb on another, perhaps even producing "rootlets" by which it clings to its living support, and yet it may not be a parasite in the proper sense of the term, for it may not absorb the slightest amount of nutritious matter except from the soil and the air. It is not at all uncommon for the Honeysuckle to twine its stems round the trunk and branches of a young tree, with the result that the tree becomes stunted, and assumes a starved appearance, especially in its lower parts; and yet the Honeysuckle is not a parasite. It has withdrawn nothing from the tree which supports it, but has coiled itself so tightly round it as to interfere with the circulation of its sap. The lower part of the tree is especially affected because the strangulating coils of the climber prevent the downward flow of the sap contained in the vessels of the bast or inner bark, and this is the sap which holds the constructive materials that have been built up in the leaves, under the influence of light.

Many of the parasitic plants are of microscopic dimensions, and others are larger species belonging to the Fungi or Mushroom group. Some, however, are flowering plants, and these only fall within the scope of our work.

We shall first deal with parasites which have no green leaves or chlorophyll, and are therefore entirely dependent on outside sources for their supply of organic material, starting with the interesting Dodders (Cuscuta), which coil themselves round herbs,shrubs, or even trees, and produce sucking organs on their stems that come in contact with their host.

These are all smooth plants, with globular clusters of yellowish-pink flowers, the calyx being of the same colour as the corolla. The former is deeply divided into four or five parts, and the corolla has four or five spreading lobes with as many scales inside its broad tube. The ovary has two distinct styles, and the fruit is a globular capsule. The following summary of distinguishing features will enable the reader to identify the British species of the genus:—

1. The Greater Dodder (Cuscuta europæa).—A plant of a greenish yellow colour, generally more or less tinged with red, with flowers in sessile, globular clusters nearly half an inch in diameter, each individual flower being about a tenth of an inch. This species is not abundant. It may be met with in hop-fields, and is also parasitic on nettles, various shrubs, and trees, including the elder and the ash.

2. The Flax Dodder (C. Epilinum).—Very much likeC. europæa, but the flowers are fewer in number, larger, and more fleshy. The calyx is nearly as long as the corolla, with sharply-pointed segments; and the corolla tube is always globular. This species is not indigenous, but is sometimes met with in flax-fields.

3. The Lesser Dodder (C. Epithymum).—A more slender plant, with thread-like stems, and flowers in small, compact, globular heads, with red calyx and cylindrical corolla. This species occurs principally on sunny heaths, where it is parasitic on shrubby plants, such as thyme and ling. It is much more common than the foregoing.

4. The Clover Dodder (C. Trifolii).—Very much like the Lesser Dodder, of which it is sometimes regarded as a variety. Its calyx is of a very pale colour, and is almost as long as the tube of the corolla, which is cylindrical in form. It is rare, but sometimes appears in undesirable numbers in clover fields.

All the species produce their flowers in August and September, butC. europæamay often be seen in bloom very early in July.

The seeds of the Dodder fall from the opened capsules during late summer and early autumn, alighting on the soil, or on the decomposing foliage that covers the ground, or on the rough barks of the tree that served as a host for the parasitic plant. The seeds of many other plants fall about the same time, but those of the Dodder do not begin to germinate until about a month later than the majority of these, in the following season, and consequentlythe young Dodder plants do not appear before their future hosts have had time to grow sufficiently large to support and nourish them. Perennial plants, too, which are attacked by the Dodder, have also produced strong shoots and leaves from their roots or underground stems by the time that the parasite begins its search for ready-made organic food; and it is clear that if the Dodder seeds germinated earlier in the season, the young plants would starve for want of suitable herbs to give them support and nourishment.

Greater Dodder, on Nettle--A Complete Plant.

When the seed germinates it sends out a filament which penetrates into the soil and fixes the seedling firmly. The other end grows upward, carrying up with it a little swollen mass of food-reserve, sufficient to support the growing seedling until it has had some chance of reaching a suitable host. The upper end of the seedling now sends out a filament which rapidly elongates, and, growing upward, searches for some stem on which to climb.

All this time the little mass of food-reserve is being rapidly exhausted, and if the young seedling fails to reach a suitable plant on which to climb it soon dies, for its lower extremity is unable to absorb sufficient food material from the soil; and the plant itself, having no chlorophyll, cannot decompose carbonic acid gas and build up organic material to add to its substance.

The Clover Dodder, with a Separate Cluster of Flowers Representing the Natural Size.

Again, should the young plant fail to reach a favourable support, so that it is of necessity compelled to trail along the ground, the filaments which would soon produce suckers when attached to a living plant have no power to form any structures capable of extracting food material from a damp soil.

Circumstances being more favourable, however, the upper filament eventually finds a stem, and immediately begins to twine itself round it, making a few close coils in a clockwise direction. Should the support prove to be a dead stem, little wartlike swellings are produced at points where the two touch, and these serve as a means of attachment for the climbing filament, but no suckers are formed. If, however, the filament surrounds a living stem, eachof the swellings gives rise to suckers that penetrate into the tissues of the latter, and withdraw the organic food necessary for the continued existence of the plant.

The Dodder now grows rapidly, giving off branches which search in all directions for additional supports, sometimes climbing from one plant to another, and producing new suckers whenever a favourable situation has been reached. The plant has now all it requires both in the way of mechanical support and nourishment, and its lower part, thus rendered useless, soon withers, breaking all connexion with the soil on which the seed originally germinated. New branches continue to form, each one producing additional suckers for the extraction of food from the host or hosts, until a tangled mass of clinging stems is the result. Then the globular clusters of little flowers appear, followed by balls of small capsules which throw off their lids when ripe, allowing the seeds to be shaken out by the wind. The Dodder plant now withers, leaving, in the autumn, its dead tangles of climbing filaments still attached to the withered herbs on which it fed, or to the branches of the tree which served as its host.

Other parasitic plants possessing no chlorophyll, and therefore incapable of building up organic compounds for themselves, derive their food from the roots of trees and shrubs.

Among these is the Toothwort (Lathræa), which is carnivorous as well as parasitic, and is described in our chapter (XXIV) dealing with carnivorous plants, so that we need only refer here to its habit as a parasite.

The seed of this plant germinates on the damp ground to which it falls in early summer. The young root penetrates into the soil, deriving its nourishment entirely from the food reserve that was stored up in the seed, and soon sends out lateral branches in search of the roots of a suitable host. If it fails to attain this end by the time that the reserve is exhausted, it dies; but if it succeeds in reaching the root of an Elm, Hazel, Hornbeam, Ash, Poplar, or other tree, it fastens itself to it, and develops suckers which penetrate into the substance of the root to extract its sap. The parasite now grows very rapidly, producing its underground stems, with their fleshy, overlapping scales, as described on p.352.

The Broomrapes of the same order (Orobanchaceæ) are very similar in their parasitic habits to the Toothwort, and, like the latter, they possess no chlorophyll. The seeds germinate on the damp soil, producing a long, narrow embryo that grows downward intothe ground until it reaches the root of some herb or shrub. It then gives off suckers which penetrate into the root, and, with the aid of the organic food thus obtained, forms a tuberous swelling on its surface. Flowering stems are afterwards produced, and these, rising above the soil, bear terminal spikes of lipped flowers, followed by capsules containing many seeds.

The Great Broomrape.

There are several British species of this genus (Orobanche), and their flowering stems, which are usually unbranched, produce scale-like leaves of the same colour as themselves. Each flower of the spike is in the axil of a bract resembling the scales of the lower part of the stem; and in some species there is a pair of smaller bracts close to the base of the calyx. The corolla is either tubular or bell-shaped, and more or less distinctly lipped. Each flower has four stamens, arranged in pairs, and a two-lobed stigma. The following outline of leading features will serve for the identification of the common Broomrapes:—

1. The Great Broomrape (O. Rapum).—A plant from twelve to eighteen inches high, of a pale yellow colour at first, but afterwards turning to a dull purple brown. Stem thick, especially below, and unbranched. Scales lanceolate. Flowers sessile, whitish, with only one bract, forming a spike from six to nine inches long. This species is moderately common, and is parasitic on the roots of Furze and Broom. Time of flowering—May to July.

2. The Clove Broomrape (O. caryophyllacea).—Very similar to the Great Broomrape in colour, but usually smaller, and easily distinguished by the sweet clove-like scent of its flowers. Spike not so dense as in the last species, and the corolla tube not so broad.The plant is not uncommon in the southern counties of England. It is parasitic on the roots of the Great Hedge Bedstraw, and flowers from May to July.

3. The Tall Broomrape (O. elatior).—Also much like the Great Broomrape, of which it is perhaps a variety. It retains its original yellowish colour for a longer period, and is parasitic on the Great Knapweed, flowering from June to August.

4. The Least Broomrape (O. minor).—A yellow or pale brown plant, from six inches to over a foot in height, more slender than the preceding species, with smaller flowers. The flowers are whitish, but more or less tinged with purple, and bloom from June to October. It is parasitic on a number of different plants, including the Ivy, Clovers, Hawkweed, Wild Carrot, &c., and is found in many districts in South and Central England.

We have now to consider those parasites which bear leaves possessing chlorophyll granules, and are therefore able to build up a portion of the organic compounds necessary for their development. Most of these, at least as far as the British flowering species are concerned, have also true roots which grow into the soil and absorb mineral food, like those of the non-parasitic plants allied to them, so that it is difficult to understand why they should require the additional nourishment stolen from the roots of neighbouring plants. One, however, the well-known Mistletoe, grows on trees at a distance from the ground, and therefore obtains the whole of its food, with the exception of carbonic acid gas, direct from its host.

This plant—the Mistletoe (Viscum album), of the orderLoranthaceæ—is attached to the tree on which it grows by a thick stem that becomes woody when old. Its branches are of a yellowish-green colour, and are repeatedly forked in such a manner as to form a dense tuft that often reaches a diameter of two feet or more. The leaves are of the same colour as the branches, and are rather thick and fleshy. The flowers grow in the forks of the branches, on very short stalks, and are imperfect, the males and females being on separate plants. The former are in clusters of about three or four, in a cuplike, fleshy bract, each flower having four thick, triangular petals with an anther on the middle. The females are either solitary or in clusters of two or three, with a similar bract, and very small petals. The fruit is a white, glutinous berry, almost transparent, with only one seed.

The Mistletoe grows on a variety of trees, including the Apple,Pear, Black Poplar, and Oak; and thrives most luxuriantly on those which have a soft tissue beneath the bark. It is found principally in the southern and western counties of England, and flowers from March to May.

Mistletoe.

There is no doubt but that the seeds of the Mistletoe are distributed from tree to tree by the agency of birds, especially the thrushes, which devour the berries in large numbers. The seed of the berry is protected by a covering which remains quite untouched by the digestive fluids of the bird, and consequently it is expelled intact with the excrement, and frequently drops to a branch of the tree, where it lodges in a crevice of the bark, and is securely fixed in its place by the slimy excrement in which it is embedded.

Here the seed germinates, sending out a little rootlet that always turns towards the bark on which it rests, and subsists for a time on the food-reserve that it contains. When the young root reaches the bark it becomes flattened against the surface, and spreads out, forming a disc that holds the seedling firmly to the tree.

A projection (thesinker) is then sent inwards from the disc, and this penetrates the bark, reaching the wood beneath, but does not enter the latter. This terminates the growth of the seedling for the first year, but as soon as the warm weather of the following spring commences, the sinker begins to spread over the surface of the outer ring of wood, while at the same time a new annual ringof wood begins to form outside, thus surrounding and banking in the sinker. It would appear, on making a section of the tree, as if the sinker had actually pushed its growth through the outer ring of wood, whereas it does not penetrate the wood at all, but is only banked up by the new wood that grows round it. This is repeated year by year, until the sinker is at last quite deeply set in the branch, being surrounded by the wood of several annual rings.

A Young Mistletoe Plant on the Branch of a Tree.The Branch is Cut Longitudinally to Show the Suckers.

During the second year's growth the sinker sends out little roots which run up and down the stem, beneath the bark, and these give rise to new sinkers that grow down to the surface of the wood, and become, in turn, embedded in the new layers of wood that form round them. And while the young Mistletoe plant is thus securing a firm hold on its host, and withdrawing ready-made organic compounds from its sap, the outer green stem develops, and soon gives rise to the first pair of leaves.

If food is obtained in abundance, as is the case when the host is a tree of a soft and sappy nature, the growth is rather rapid; but otherwise the development is comparatively slow. In any case the age of the parasite may be ascertained by counting the number of annual rings of wood that lie outside the deepest sinker; and by this means it has been found that the Mistletoe may attain an age of over thirty years.

We have now to consider a group of plants, the parasitic habits of which would scarcely be suspected by an ordinary observer. They are green plants, with well-developed foliage leaves, and true roots which absorb mineral food from the soil. Their seedlings grow in the same way as those of non-parasitic species, deriving no nourishment from neighbouring plants, but obtaining all their food from the air and the soil, and building up all the organic compounds required for their growth by the agency of their own chlorophyll.

It is difficult to understand why these plants should afterwards produce suckers on their roots in order to obtain nourishment from other species, but they do this, and experiments have proved that the food thus obtained is more or less essential to their development. Some of them die while still young if grown apart from other species,and the others, under similar conditions, though they reach what we may term the adult stage, remain somewhat weak and stunted, and produce but few flowers and fruits.

Most of the plants referred to belong to the orderScrophulariaceæ, and among them we may mention the Eyebright (Euphrasia), the Yellow Rattle (Rhinanthus), the Cow-wheat (Melampyrum), and the Lousewort (Pedicularis). They generally appear in large numbers close together, often in such abundance as to determine the general colour of the ground on which they grow, and yet they do not apparently cause much damage to the grass and other plants which they rob.

These green parasites are described in various chapters, according to their habitats and their flowering seasons; so we shall do no more here than to briefly refer to their parasitic habits.

The Eyebright (p.274) grows on heaths and downs, where it derives organic food from the roots of the neighbouring grasses. The Lousewort, too (p.118), which grows in marshes and moist meadows, is parasitic principally on the roots of grasses, apparently without affecting the latter. The last-named species is a perennial, the roots of which have to find hosts that are capable of supporting it year by year. If the host of the present year should happen to die in the autumn, the suckers that were attached to its roots soon die, and the parasite has to seek a new source of supply. This it does by extending its roots until it reaches a new host, and then producing new suckers. Thus we are able to understand the origin of the long roots so often seen on the Lousewort, and also the reason why these roots never grow downwards into the soil, but always horizontally, just beneath the surface. Further, since the roots extend themselves in search of food at times when the supply is temporarily diminished or stopped, it is clear that some reserve is necessary for the elongation referred to. Such a reserve exists in the older, thick portion of the perennial root, near the base of the stem.

In the case of the Cow-wheat (p.146) no suckers are produced until the lateral branches of the root of the seedling reach a moderate length; but in order to increase the chances of finding a suitable host these branches are developed in large numbers, and extend themselves in all directions. The suckers produced on them cling very firmly to the root-fibres of the host, which they almost completely embrace.

The suckers of the Yellow Rattle (p.118) are globular, often nearly one-eighth of an inch in diameter, and partly surround the root-fibres of the plants to which they are attached.

Quite a number of plants, belonging to different orders, are provided with the means of capturing small animals, and of digesting their prey and absorbing the nutrient matter thus obtained into their own systems. In this way they are enabled to obtain nitrogenous material which, in the ordinary way, is absorbed in the form of mineral solutions, from the soil, by the agency of the roots. The greater number of these carnivorous plants are to be found in tropical lands; but a few are British, and are of such an interesting nature that we propose to devote a short chapter to a description of their peculiar structure and habits.

The plants to which we refer are often spoken of as insectivorous species; but although in nearly all cases the animal food consists almost entirely of insects, it is not entirely derived from this one group of animal life, and therefore the term carnivorous is rather more appropriate.

In pools we sometimes meet with floating plants that have no true roots, at least at the time of flowering, but consist of a tuft of long, rootlike, submerged branches, bearing much-divided leaves, and sending leafless stalks of yellow flowers above the surface of the water. These plants are the Bladderworts (Utricularia), of the orderLentibulaceæ, and are so called because they have little air-bladders either attached to the leaves or supported on leafless branches.

The leaves are divided into numerous very narrow segments, thus presenting a proportionately large amount of surface to the water for the absorption of dissolved gases required by the plant; and the flowers consist of a deeply two-lobed calyx; a spurred corolla, with its mouth closed or nearly closed by means of a convex'palate'; two stamens; and a one-celled ovary that ripens into a globular fruit.

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