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 pyc. 143, — A, Dodder (Cuscuta Euro- 
thread-like seedlings are sen- pea) living 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 may having penetrated the tissues of the Hop 
chance to hit in their growth. Vine After Kerner. 
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 little 
Dodder seed is undesirable for seeding. (Fig. 143.) 
The Mistletoe lives 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 Roots 
The production of new plants from seeds, stems, leaves, or roots 
is called plant propagation. Since roots readily produce adven- 
titious buds which can develop into new plants, they are much 
