Parasitic Plants

Collier's New Encyclopedia (1921)

those which, unable to nourish themselves, prey upon other plants or animals; becoming attached, they gain access to the tissues of their host and feed upon its juices. The mistletoe has no roots in the ground; its seed is left by a bird on an apple or an oak tree, to which, when it begins to grow, it becomes attached by means of special organs called haustoria, which act as roots and enable it to draw crude sap, water, and salts from its host, and having green leaves it can absorb carbonic acid from the air, and elaborate food for its tissues. In the case of the dodder, again, which begins life as an independent plant, the seed germinates underground; when the young plant reaches the surface it fastens upon some host, twining round it, sending its haustoria deep into the tissues, and drawing all its nourishment from them; it bears no green leaves, but only flowers, while the part in the ground dies. There are some parasites which are attached to the roots instead of the stems of their hosts-e. g., yellow rattle, cow wheat, eyebright. The attachment by the haustoria is always remarkably intimate; their tissues are always joined to the corresponding ones of the host, often in such a way that it is difficult to say to which plant they belong. Allied to parasitism is symbiosis, a sort of mutually arranged parasitism for the benefit of both parties; as in the case of the lichens, which consist of algæ and fungi in partnership. But the most important and interesting of the vegetable parasites are those belonging to the schizomycetes or bacteria, whose study has assumed such prominence. The relations of these organisms to their host are much more intimate than in the case of the larger parasites, and the problems presented by the disease associated with them are consequently much more difficult of solution; but in some cases the parasitic nature of these diseases has been completely established. PARCE. See FATES.