1911 Encyclopædia Britannica/Ivy
IVY (A.S. ifig, Ger. Epheu, perhaps connected with apium, ἄπιον), the collective designation of certain species and varieties of Hedera, a member of the natural order Araliaceae. There are fifty species of ivy recorded in modern books, but they may be reduced to two, or at the most, three. The European ivy, Hedera Helix (fig. 1), is a plant subject to infinite variety in the forms and colours of its leaves, but the tendency of which is always to a three- to five-lobed form when climbing and a regular ovate form of leaf when producing flower and fruit. The African ivy, H. canariensis, often regarded as a variety of H. Helix and known as the Irish ivy, is a native of North Africa and the adjacent islands. It is the common large-leaved climbing ivy, and also varies, but in a less degree than H. Helix, from which its leaves differ in their larger size, rich deep green colour, and a prevailing tendency to a five-lobed outline. When in fruit the leaves are usually three-lobed, but they are sometimes entire and broadly ovate. The Asiatic ivy, H. colchica (fig. 2), now considered to be a form of H. Helix, has ovate, obscurely three-lobed leaves of a coriaceous texture and a deep green colour; in the tree or fruiting form the leaves are narrower than in the climbing form, and without any trace of lobes. Distinctive characters are also to be found in the appendages of the pedicels and calyx, H. Helix having six-rayed stellate hairs, H. canariensis fifteen-rayed hairs and H. colchica yellowish two-lobed scales.
|Fig. 1.—Ivy (Hedera Helix) fruiting branch.|
1. Flower. 2. Fruit.
|Fig. 2.—Hedera colchica.||Fig. 3.—Climbing Shoot of Ivy.|
The Australian ivy, H. australiana, is a small glabrous shrub with pinnate leaves. It is a native of Queensland, and is practically unknown in cultivation.
It is of the utmost importance to note the difference of characters of the same species of ivy in its two conditions of climbing and fruiting. The first stage of growth, which we will suppose to be from the seed, is essentially scandent, and the leaves are lobed more or less. This stage is accompanied with a plentiful production of the claspers or modified roots by means of which the plant becomes attached and obtains support. When it has reached the summit of the tree or tower, the stems, being no longer able to maintain a perpendicular attitude, fall over and become horizontal or pendent. Coincidently with this change they cease to produce claspers, and the leaves are strikingly modified in form, being now narrower and less lobed than on the ascending stems. In due time this tree-like growth produces terminal umbels of greenish flowers, which have the parts in fives, with the styles united into a very short one. These flowers are succeeded by smooth black or yellow berries, containing two to five seeds. The yellow-berried ivy is met with in northern India and in Italy, but in northern Europe it is known only as a curiosity of the garden, where, if sufficiently sheltered and nourished, it becomes an exceedingly beautiful and fruitful tree.
It is stated in books that some forms of sylvestral ivy never flower, but a negative declaration of this kind is valueless. Sylvestral ivies of great age may be found in woods on the western coasts of Britain that have apparently never flowered, but this is probably to be explained by their inability to surmount the trees supporting them, for until the plant can spread its branches horizontally in full daylight, the flowering or tree-like growth is never formed.
A question of great practical importance arises out of the relation of the plant to its means of support. A moderate growth of ivy is not injurious to trees; still the tendency is from the first inimical to the prosperity of the tree, and at a certain stage it becomes deadly. Therefore the growth of ivy on trees should be kept within reasonable bounds, more especially in the case of trees that are of special value for their beauty, history, or the quality of their timber. In regard to buildings clothed with ivy, there is nothing to be feared so long as the plant does not penetrate the substance of the wall by means of any fissure. Should it thrust its way in, the natural and continuous expansion of its several parts will necessarily hasten the decay of the edifice. But a fair growth of ivy on sound walls that afford no entrance beyond the superficial attachment of the claspers is, without any exception whatever, beneficial. It promotes dryness and warmth, reduces to a minimum the corrosive action of the atmosphere, and is altogether as conservative as it is beautiful.
The economical uses of the ivy are not of great importance. The leaves are eaten greedily by horses, deer, cattle and sheep, and in times of scarcity have proved useful. The flowers afford a good supply of honey to bees; and, as they appear in autumn, they occasionally make amends for the shortcomings of the season. The berries are eaten by wood pigeons, blackbirds and thrushes. From all parts of the plant a balsamic bitter may be obtained, and this in the form of hederic acid is the only preparation of ivy known to chemists.
In the garden the uses of the ivy are innumerable, and the least known though not the least valuable of them is the cultivation of the plant as a bush or tree, the fruiting growth being selected for this purpose. The variegated tree forms of H. Helix, with leaves of creamy white, golden green or rich deep orange yellow, soon prove handsome miniature trees, that thrive almost as well in smoky town gardens as in the pure air of the country, and that no ordinary winter will injure in the least. The tree-form of the Asiatic ivy (H. colchica) is scarcely to be equalled in beauty of leafage by any evergreen shrub known to English gardens, and, although in the course of a few years it will attain to a stature of 5 or 6 ft., it is but rarely we meet with it, or indeed with tree ivies of any kind, but little attention having been given to this subject until recent years. The scandent forms are more generally appreciated, and are now much employed in the formation of marginal lines, screens and trained pyramids, as well as for clothing walls. A very striking example of the capabilities of the commonest ivies, when treated artistically as garden plants, may be seen in the Zoological Gardens of Amsterdam, where several paddocks are enclosed with wreaths, garlands and bands of ivy in a most picturesque manner.
About sixty varieties known in gardens are figured and described in The Ivy, a Monograph, by Shirley Hibberd (1872). To cultivate these is an extremely simple matter, as they will thrive in a poor soil and endure a considerable depth of shade, so that they may with advantage be planted under trees. The common Irish ivy is often to be seen clothing the ground beneath large yew trees where grass would not live, and it is occasionally planted in graveyards in London to form an imitation of grass turf, for which purpose it is admirably suited.
The ivy, like the holly, is a scarce plant on the American continent. In the northern United States and British America the winters are not more severe than the ivy can endure, but the summers are too hot and dry, and the requirements of the plant have not often obtained attention. In districts where native ferns abound the ivy will be found to thrive, and the varieties of Hedera Helix should have the preference. But in the drier districts ivies might often be planted on the north side of buildings, and, if encouraged with water and careful training for three or four years, would then grow rapidly and train themselves. A strong light is detrimental to the growth of ivy, but this enhances its value, for we have no hardy plants that may be compared with it for variety and beauty that will endure shade with equal patience.
The North American poison ivy (poison oak), Rhus Toxicodendron (nat. order Anacardiaceae), is a climber with pinnately compound leaves, which are very attractive in their autumn colour but poisonous to the touch to some persons, while others can handle the plant without injury. The effects are redness and violent itching followed by fever and a vesicular eruption.
The ground ivy, Nepeta Glechoma (nat. order Labiatae), is a small creeping plant with rounded crenate leaves and small blue-purple flowers, occurring in hedges and thickets.