THE ORGANIZATION OF THE PLANT 



59 



Roots. The root, or underground portion, of the plant is 

 the first to put forth from the germinating seed. No matter 

 in what position the seed may happen to be lying when growth 

 begins, the root, in response to gravity, tends to grow straight 

 downward, often curving considerably to do so. This is of 

 great advantage to the young plant, since it quickly brings 

 it into contact with the neces- 

 sary moisture and other food 

 materials, and also gives it a 

 hold in the soil. The root, how- 

 ever, is not pulled down by 

 gravity, but simply uses this 

 force as a guide. After reach- 

 ing the soil it may turn aside 

 for moisture or food materials, 

 or to avoid obstacles, such as 

 stones, in the soil. In its search 

 for moisture it often goes 

 long distances. Instances are 

 known where the roots of a 

 tree have in this way filled 

 drains three hundred feet away. 

 Soon after penetrating the soil 

 the first root begins to give 

 off branches, and these branch 

 and branch again, spreading 

 out laterally and thoroughly exploring the soil for food mate- 

 rials. These lateral roots are often very numerous. A single 

 corn plant may have enough roots to measure a quarter of a 

 mile or more when placed end to end. In humid regions 

 roots seldom descend more than four or five feet, but in arid 

 regions they may go much deeper. The main root of such 

 plants as mesquite, shepherdia, and alfalfa have been known 

 to go down fifty or sixty feet in search of moisture. 



FIG. 32. Wild hyacinth (Camassia) 

 with multiple primary roots 



