VI. THE ORGANS OF NUTRITION IN PLANTS — THE 

 SOIL AND ITS RELATION TO THE ROOTS 



Problem. — What (i plant takes froin the soil and how it gets 

 it. 



{a) What determines the direction of growth of roots ? 



(h) Hoiv is the root built ? 



(c) How does a root absorh water ? 



id) What is in tl%e soil that a root might tahe owt ? 



{e) Why is nitrogen necessary, and how is it obtained ? 



Laboratory Suggestions 



Demonstration. — Roots of bean or pea. 



Demonstration or home experiment. — Response of root to gfravity and to 

 water. What part of root is most responsive ? 



Laboratory work. — Root hairs, radish or corn, position on root, gross 

 structure only. Drawing. 



Demonstration. — Root hair under compound microscope. 



Demonstration. — Apparatus illustrating osmosis. 



Demonstration or a home experiment. — Organic matter present in soil. 



Demonstration. — Root tubercles of legume. 



Demonstration. — Nutrients present in some roots. 



Uses of the Root. — If one of the seedlings of the bean spoken of 

 in the last chapter is allowed to grow in sawdust and is given 

 light, air, and water, sooner or later it will die. Soil is part of 

 its natural environment, and the roots which come in contact ^\^th 

 the soil are very important. It is the purpose of this chapter to 

 find out just how the young plant is fitted to get what it needs 

 from this part of its environment ; namely, the soil. 



The development of a bean seedling has sho^vn us that the root 

 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 ichere 

 it is to develop. It has many other uses, as the taking in of water 

 with the mineral and organic matter dissolved therein, the stor- 



71 



