146 



GREEN PLANTS AS FOOD MAKERS 



surface of the root hair. The soil contains, besides chemical com- 

 pounds of various mineral substances, — lime, potash, iron, silica, 

 and many others, — much organic material. Acids of various kinds 

 are present in the soil. They dissolve certain mineral substances 

 in the water which is absorbed by the root hairs. Root hairs also 

 give off small amounts of acid, which assist in dissolving minerals. 



• tf ops 



dilutee 

 cccict = 



water 

 audi 



phenolph 



and 



enoirgh 



base 



to turn 



pink 



A solution of phenolphthalein will lose its color if an acid is added to it. Explain why the 

 solution of phenolphthalein (on the right) is losing its color. 



We say that the delicate root hairs absorb water, and since 

 absorption is a process common to both plants and animal cells 

 we shall study this phenomenon carefully in the next problem. 



Self-Testing Exercise 



A root is made up of (1). The outer layer, called the 



(2), is prolonged into many (3) walled structures 



called (4) (5). These take (6) and 



(7) (8) out of the soil. Root hairs give off a small 



amount of (9), which aids in (10) mineral salts. 



