72 



SOIL AND ITS RELATION TO ROOTS 



A root system, showing primary 

 and secondary roots. 



age of food, climbing, etc. All 

 functions other 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 the dirt from the roots, you 

 will see that a long root is devel- 

 oped as a continuation of the hy- 

 pocotyl. 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 



growing root ? This question may be 



answered by a simple experiment. 

 Plant mustard or radish seeds in a 



pocket garden, place it on one edge 



and allow the seeds to germinate until 



the root has grown to a length of about 



half an inch. Then turn it at right 



angles to the first position and allow it 



to remain for one day undisturbed. 



The roots now will be found to have 



turned in response to the change in 



position, that part of the root near 



the growing point being the most 



sensitive to the change. This ex- 

 periment seems to indicate that the Revolve this figure in the direc- 



roots are influenced to grow downward *" 

 by the force of gravity, spond to gravity. 



