164 ROOTS 



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 

 absorbmg 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 pi^ 143 _ ^^ Dodder (Cuscuta Euro- 

 thread-like seedUngs are sen- ^csa) 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 ^avhig 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 Uttle 

 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 



