54 BIOLOGY FOR BEGINNERS 



large extent of surface for absorption. The roots of the grasses, 

 for instance, are so numerous that they hold the soil together, 

 forming a compact layer called the " turf." 



Tap Roots are greatly enlarged primary roots which enable the 

 plant to go deep after water supply and hold firmly in the ground. 

 The thistle, dandelion, burdock, and many more of our worst 

 weeds are thus adapted to make a living under adverse 

 circumstances. 



Fleshy Roots are adapted for storage of food stuffs and have the 

 main part greatly thickened, as in the carrot, turnip, and beet. 

 They are generally found in plants which require two seasons 

 to mature their seed and so need stored food to carry them over 

 the winter. In other cases, as the dahlia and sweet potato, the 

 fleshy root is used to reproduce the plant. 



Aerial Roots. Some tropical orchids which live attached to 

 trees and never reach the earth at all develop aerial roots. They 

 have a very thick, spongy cortex, which absorbs water from the 

 moist ah* of the forests. 



Aquatic Roots. These are found in a few floating plants such 

 as the duck- weed and water hyacinth. They are usually small, 

 few in number, and lacking hi root hairs. They do not need 

 extra surface for absorption because they are surrounded by an 

 abundant water supply. 



ADVENTITIOUS ROOTS 



Brace Roots. From the stems of corn and many other grasses, 

 develop brace roots, which help to support the slender stems or to 

 raise them again if they are bent down. 



Roots for Propagation. In certain plants if the stem lies in 

 contact with the soil for a sufficient length of time, roots will 

 spring from the joints and produce new plants. The stems of 

 various berry bushes can thus be fastened to the earth " staked 

 down " and will take root in this way. The new root systems, 

 when sufficiently developed, can be separated from the parent 

 plant to make a new berry bush. 



