VII. ROOTS AND THEIR WORK 

 Problem XIV. A study of roots. {Laboratory Manual, Prob. 



(a) Factors influencing direction of growth. 



(&) Structure. 



(c) How they absorb soil water. 



The development of a bean seedling has shown us that the root 

 invariably grows first. One of the most important functions of the 

 root to a young seed plant is that of a holdfast, an anchor to fasten it in 



the place where it is to develop. In 

 this chapter we shall find many 

 other uses of the root to the plant, 

 the taking in of water and the 

 mineral and organic matter dis- 

 solved therein, the storage of food, 

 climbing, etc. All other functions 

 than the first one stated arise after 

 the young plant has begun to 

 develop. 



Root System. If you dig up a 

 young bean seedling and carefully 

 wash off the roots, you will see that 

 a long root is developed as a con- 

 tinuation of the hypocotyl. This 

 root is called the primary root. 

 Other smaller roots which grow 

 from the primary root are called secondary, or tertiary, depending 

 on their relation to the first root developed. 



Downward Growth of Root. Influence of Gravity. Most of the 

 roots examined take a more or less downward direction. We are 

 all familiar with the fact that the force we call gravity influences life 

 upon this earth to a great degree. Does gravity act on the grow- 

 ing root ? This question may be answered by a simple experiment. 



84 



A root system, showing primary and 

 second roots. 



