Foundations of botany (1901) (14783869822)

Identifier: foundationsofbot00berg (find matches)
Title: Foundations of botany
Year: 1901 (1900s)
Authors: Bergen, Joseph Y. (Joseph Young), 1851-1917 Bergen, Joseph Y. (Joseph Young), 1851-1917. Bergen's Botany: key and flora, Northern and Central States ed. 1901
Subjects: Plants
Publisher: Boston : Ginn
Contributing Library: The LuEsther T Mertz Library, the New York Botanical Garden
Digitizing Sponsor: The LuEsther T Mertz Library, the New York Botanical Garden



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e host. Someparasites are seed-plants, but a far greater number ofspecies are spore-plants. 405. Half-Parasitic Seed-Plants. — Half-parasites or par-tial parasites are those which take a portion of their food (orof raw materials to make food) from their host and manu-facture the rest for themselves. Usually they take mainlythe newly absorbed soil-water from the host and do theirown starch-making by combining the carbonic acid gas,which they absorb through their leaves, with the waterstolen by the parasitic roots or haustoria imbedded in thewood of the host. Evidently the needed water may justas well be taken from the underground parts of the hostas from the upper portions, and accordingly many half-parasites are parasitic on roots. This is the case withmany of the beautiful false foxgloves (Gerardia), with thepainted-cup (Castillea), and some species of bastard toad-flax (Comandra); see Flora. Usually these root-parasitesare not recognized by non-botanical people as parasites at 336
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Plate IX. — A Cottonwood covered with Mistletoe PARASITES 337 all, but in Germany a species common in grain fields ^ andthe eyebright, which abounds in grass fields, are respectivelyknown as hunger and milk-thief, from the injurythey do to the plants on which they fasten themselves.The mistletoe is a familiar example of a half-parasite,which roots on branches (Plate IX). Among the scantybelts of Cottonwood trees along streams in New Mexico itis necessary to lop off the mistletoe every year to give thetree any chance to grow. Half-parasites may be knownfrom plants that are fully parasitic by having green orgreenish foliage, while complete parasites have no chloro-phyll and so are not at all green. 406. Wholly Parasitic Seed-Plants. — These are so nearlydestitute of the power of assimilation that they must robother plants of all needed food or die of starvation. Some,like the cancer-root (see Flora), are root-parasites; others,like the dodder, are parasitic on stems above ground. Th