224 A YEAR IN SCIENCE 



water, and the Mexican farmers in digging wells follow 

 these roots as guides. Where water is more abundant, 

 the mesquite forms a good-sized tree, with much 

 shorter roots.''* 



Questions 



1. State two important functions of roots. 



2. Define tap root and give examples. 



3. What is meant by fibrous roots? Give examples. 



4. Describe root hairs. 



5. What substances diffuse into the plant through 

 the root hairs ? What substances pass out of the root ? 



6. Do plant excretions have any effect on the 

 fertility of soil? 



7. How does the size of the root system of a tree 

 compare with that of its branches? 



8. How do you account for the fact that desert 

 plants have such large root systems? 



'"'Bergen and Davis, Principles of Botany. Ginn and Company. 



