. Botany for agricultural students . Botany. PARASITIC ROOTS 163 they are growing in wet shady places, are not in a good position for absorption. Air roots of climbers, as in the Poison Ivy, do no absorbing, and serve only to attach the plant to the support. Those air roots that absorb usually have no root hairs, and the absorbing is done by a sponge-like mantle of cells, called velamen, covering the root. In some cases, as in many tropical climbers, the air roots reach to the ground or to cup-shaped leaves where water is obtained. The air roots of the Orchids which live on damp tree trunks or
. Botany for agricultural students . Botany. PARASITIC ROOTS 163 they are growing in wet shady places, are not in a good position for absorption. Air roots of climbers, as in the Poison Ivy, do no absorbing, and serve only to attach the plant to the support. Those air roots that absorb usually have no root hairs, and the absorbing is done by a sponge-like mantle of cells, called velamen, covering the root. In some cases, as in many tropical climbers, the air roots reach to the ground or to cup-shaped leaves where water is obtained. The air roots of the Orchids which live on damp tree trunks or rocks of tropical countries take up moisture when there is rain or dew. Such plants, called epiphytes, flourish without the assistance of soil roots. Parasitic Roots. — There are a large number of plants, called parasites, that depend upon other plants for food. The Dodder is dependent upon other plants for its food and obtains it by sending roots into the plant upon which it is grow- ing. Dodder has no food- making pigment and the young seedling soon perishes unless it can obtain food from some other plant. The pj^ 143 _ ^_ Do^^er (Cmcuta Euro- thread-like seedhngs are sen- pcea) Uving on a Hop Vine; B, diagram- sitive to touch and coil about matic drawing of a cross section of the weeds, Clover, Alfalfa, or Hop Vine showing the roots of the Dodder other plants which they mav having penetrated the tissues of the Hop chance to hit in their growth. ^'''^- After Kemer. If the plant has suitable food, then the Dodder grows roots into its tissues and absorbs food from it. Clover, Flax, and Alfalfa are attacked in this way and much injured by Dodder. Dodder is considered a destructive weed, and seed containing only a httle Dodder seed is undesirable for seeding. {Fig. 143.) The Mistletoe hves upon trees, the roots penetrating the branches and withdrawing the necessary foods. Many plants, such as the Beech Drop, Broom Rape, etc., live on the roots of other plants. Propagation by R
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
