Parasitic plant

“ They say that when you see an orchid growing as a parasite on a tamarind tree, you should dress in white, take a new earthenware pot, then climb the tree at noon, break off the plant, put it in the pot, and let the pot fall to the ground. After that you make in the pot a decoction which confers the gift of invulnerability.257 Thus just as in Africa the leaves of one parasitic plant are supposed to render the wearer invulnerable, so in Cambodia a decoction made from another parasitic plant is considered to render the same service to such as make use of it, whether by drinking or washing. ”

“ Insects and diseases are frequently so closely united, or so dependent upon each other, that the naturalist often finds it difficult to determine to which the fruit grower should attribute his losses. Some species of insects attack only diseased or dead plants; others only the living and healthy. If a plant shows signs of failing, we are inclined to speak of it as being diseased, whether the failure is caused by a lack of some element in the soil, attacks of parasitic fungi, or noxious insects. ”

“ And so the parasitic higher plant tends to lose its division into stem and leaves and roots, and to acquire a compact and amorphous body. The animal has no longer to seek its food, and the lithe segmentation of a body adapted for locomotion becomes replaced by a squat or insinuating form. Jaws give place to sucking and piercing tubes, the alimentary canal becomes simplified, or may disappear altogether, the parasite living in the juices of its host, and absorbing them through the skin. ”

“ Another instructive instance of parasitism stimulating growth may be observed at this season in any patch of the common field thistle. Some of the plants are almost sure to be affected by a parasitic fungus. It is present in the stole of the plant, and its influence will cause the affected plants to put forth leaves earlier than the healthy ones. They will also grow faster, and in the course of a month be twice the height of their fellows. The fungus grows in the stem, and finally it will flower out on the surface of the leaves. ”

“ There are parasitic plants that flourish only on trees of some few species, and others that have particular animals for their habitats—as the fungus which is fatal to the silk-worm, or that which so strangely grows out of a New Zealand caterpillar. Of animal-parasites various kinds lead lives involving specialities of distribution. ”

“ And not only is practically the whole enormous group of moths and butterflies to be regarded as parasitic, but the same is true also of untold legions of plant-lice, scale-insects and beetles. Hyperparasitism, which may be regarded as a kind of permutation of parasitism, must also be mentioned in this connection, because it gives us a glimpse of the virgin fields which the holometabolic insects, owing to their peculiar method of development, are beginning to invade. ”

“ Some of the variations in grafted plants are found to predispose the plant to disease, or the reverse, and cases may be cited where the resulting shoots, foliage, or fruits, or seedlings more readily fall a prey to, or resist, parasitic fungi and insects than the ungrafted plants. ”

“ Our perceptions differentiate but imperfectly symptoms which are due to very different causes and reactions, probably because the organization of the plant is so much less highly specialized than that of higher animals. The yellowing and subsequent casting of leaves, for instance, is a very general symptom of disease in plants, and may be induced by drought, extremes of temperature, insufficient or excessive illumination, excess of water at the roots, the action of parasitic Fungi, insects, worms, &c., or of poisonous gases, and so forth ”

“ Or let a vigorous tree meet with an accident, and like an injured deer it becomes food for an enemy. If lightning, wind, or sleet split the bark or break a limb, through these wounds some spore or borer will speedily reach the tree's vitals. In many cases the deadly work of parasitic plants and fungi is interrelated with, and almost inseparable from, the destructive operations of predacious insects. Many so-called tree diseases are but the spread of rot and fungi through the wood by means of an entrance bored by a borer, weevil, or beetle. ”

“ Club-root or club-foot is a well-known disease. The parasite lives in the soil. Practice crop rotation. Set only healthy plants. Do not use manure containing cabbage refuse. If necessary to use infested land, apply good stone lime, 2 to 5 tons per acre. Apply at least as early as the autumn before planting; two to four years is better. Lime the seed-bed in same way.
Carnation rust.—This disease may be recognized by the brown, powdery pustules on the stem and leaves. Plant only the varieties least affected by it. Take cuttings only from healthy plants. ”

“ Even grafting of allied species of Grapes sometimes results in the young plants sending roots through the tissues of the scion, eventually reaching the earth by way of the body of the host. In such cases, the parasite also draws nutriment from its messmate by means of a superior osmotic pressure.
Almost everything lies in the point of view. No man, no animal, no plant is so debased and degraded that it does not radiate some little measure of helpfulness. ”

“ Any plants desirable for economic use or for beauty of foliage and flower become generally distributed, their parasites are removed from the regions where harmonious parasitic inter-relations have been established, and in new regions the parasites may not find the former restrictions to their growth. ”

“ The breeding of plants resistant to specific diseases not readily amenable to other means of control must proceed. Such work is now in progress with cotton, melons, tomatoes, tobacco, grains, flax and other plants. The relation existing between many root fungi and bacteria and the roots they inhabit remains to be studied. Aside from parasitism there is also mutualism, a kind of beneficial disease falling to the province of plant pathology. ”

“ The pea-vine and the rose-bush may sometimes suffer, but generally the leaves attacked have pretty well done the season's work before the parasite attains its maximum, so that man's interest in the matter is not specially affected. There is, however, another and different set of leaf-fungi whose parasitism is decidedly more intimate, and consequently destructive of the host-plant, suicidal as such a policy would seem to be. These latter, as indeed all the fungi already cited, are known as blights, and as such some species are already famous. ”

“ Such a parasite—Plasmodiophora brassicæ—enters the young root cells of a cabbage, stimulates those cells to an unwonted degree of multiplication until great tumors are formed giving rise to the vegetable disease known as 'club-root.' The plant cells become storage reservoirs of the spores of Plasmodiophora, and when the plant dies down the spores are liberated in the soil. ”

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17 In Venezuela and Colombia the word parasita—parasite—is usually employed to designate all orchids, no matter what may be the species or genus. This is a mistake. Orchids are not parasites which, like the dodder or mistletoe, obtain their nourishment from the plant or tree on which they grow. They are epiphytes, that get their nourishment from the surrounding atmosphere, and use the branches and trunks of trees merely as supports or resting-places. ”

“ Pedicularis, the louse wort, Rhinanthus, the rattle, Melampyrum, the cow-wheat and Bartsia are all partly parasitic on the roots of other plants. The Orobanchaceae or broomworts, are all destitute of chlorophyll and have scale-leaves; they are parasitic on the roots of other plants, species attacking various Leguminosae, ivy, hemp and hazel. The Cytinaceae are true parasites devoid of chlorophyll and leaves, with deformed bodies and conspicuous flowers or inflorescences. Most of them are tropical, and the group is widely scattered throughout the world. The Santalales are all parasitic ”

“ The disease is contracted from spores present in the soil, which enter the root. The parasite develops within the living cells of the plant, forming a glairy mass of protoplasm known as the plasmodium, the form of which alters from time to time. The cells which have been attacked increase enormously in size and the disease spreads from cell to cell. Ultimately the plasmodium becomes resolved into numerous minute round spores which, on the decay of the root, are set free in the soil. A preventive is quicklime, the application of which destroys the spores in the soil. ”

“ This is carried still further in the case of such root-parasites as Orobanche, where the host-plant is burdened with the whole support of the pest, because the latter, having no chlorophyll, is entirely dependent on the former for all its food.
Even ordinary climbing plants may injure others by shading them, either by scrambling over their branches—e.g. ”

“ The fungus seems, on the other hand, to stimulate the algal cells to special development, for those in the lichen are larger than those in the free state, but this is not necessarily adverse to the idea of parasitism, for it is well known that an increase in the size of the cells of the host is often the result of the attacks of parasitic fungi. It must be borne in mind that the exact nutritive relations of the two constituents of the lichen have not been completely elucidated, and that it is very difficult to draw the line between symbiosis and parasitism. ”

“ The various degrees of parasitism are to a certain extent explained by the foregoing. In order that a Fungus may enter a plant, it must be able to overcome not merely the resistance of cell-walls, but that of the living protoplasm ”

“ The procedure almost invariably followed where parasites are concerned, consists in either dusting the plants with some chemical in the form of a powder, or spraying it with a liquid, or occasionally in enveloping the plant in some gas, in each case poisonous to the insect- or fungus-pest. The principal rules to be observed are: (1) the poison employed must be sufficiently strong or concentrated to kill the parasite, but not sufficiently powerful to injure the host ”

“ That a parasite may be prevented from successfully attacking a particular plant is shown by the failure of Cuscuta to establish its haustoria in poisonous plants such as Euphorbia, Aloe, etc., and it has been pointed out that poisonous secretions in the cells of the plant protect them against the penetration of fungi. ”

“ There are weeds that worry, and seeds that fail. There are garden pests of every variety. The mice nibble away the tulip-bulbs: the canker gets into the rosebud, and the green fly infests the rose. Wire-worms destroy the roots of tender annuals, and slugs breakfast upon their sprouting leaves. Moles and birds and caterpillars have each and all their peculiar plans for vexing the gardener’s heart. Then again certain plants are attacked by special diseases of their own. The gladiolus turns yellow and comes to nothing, and a parasitic fungus destroys the hollyhock. ”

“ The fibres of the parasite never penetrate beyond their original attachment; in the adult the sucker-bearing shoots frequently run to a considerable distance, many plants being literally covered with parasites, all of which have originated from one and the same seed. ”

“ The Doctor explained that in this case the parasite was not a vine, but a distinct tree that grew from a seed deposited by the wind or by the birds on the trunk or among the leaves of a palm. It grows much faster than the palm, and in a few years the palm dies and the parasite lives. It is held in the air by the decaying stem of the parent tree until the latter altogether rots away and falls. When once the parasite has obtained a hold, the destruction of the palm is only a question of time. ”

“ If left in a foul state they spread the infection to all around. In the space at our command it is only possible to notice a few of the garden pests, and we begin with one of the most frequent and troublesome of plant foes. ”

“ Not only may such insects weaken the infested plants, but they also cause the destruction of chlorophyll, interfere with the normal functioning of the stomata, and have a toxic effect upon the tissues; further, many serious plant diseases are carried and spread by sucking insects, whilst the punctures made when feeding may allow the entry of disease spores. ”

“ The one remarkable thing which attracts attention to these growths and causes them to be mistaken for flowers is the great proportions attained by them. The 'stem,' which of course is a limb of the host plant, rarely exceeds an inch and a half in diameter, the parasite evidently not being able to attack other than the younger and more vigorously growing shoots. ”

“ Many so-called weeds are, however, partially parasitic, with their roots on the roots of others—e.g. Rhinanthus, Thesium, etc., and much damage is done to meadow grasses and herbage by the exhaustive tax which these semi-parasites impose. ”

“ His conclusions, after thorough scientific laboratory and field work covering a period of over twenty years, is that it is caused by a weak parasitic fungus attacking rapidly only when the host tree is in a weakened condition; that it may lie practically dormant in vigorous trees and that it may be successfully combatted by fertilizing, mulching, providing necessary water in time of drought and avoidance of any condition that might weaken the tree. ”

“ The insects and diseases that attack garden plants are legion; and yet, for the most part, they are not very difficult to combat if one is timely and thorough in his operations. These difficulties may be divided into three great categories: the injuries wrought by insects; the injuries of parasitic fungi ”