Roots and Their Environment 195 



important sources of food. The sugar beet is the most im- 

 portant domestic source of sugar in the United States. The 

 roots of sassafras, rhubarb, ginseng, aconite, and ipecac are 

 used in medicine. In the past many other roots were collected 

 for the same purpose. The roots of plants are used by man 

 much less than are stems and leaves. Perhaps roots are in 

 general less useful ; but the failure to utiHze them more gen- 

 erally is in part accounted for by the difficulty of harvesting 

 them and by our lack of knowledge concerning uses that 

 might be made of them. 



PROBLEMS 



1. What states produce sugar from the sugar beet? 



2. What states produce sweet potatoes? 



3. How are roots made use of in the jetties at the mouth of the Mississippi 

 River ? 



4. Why do trees along city streets frequently die when the street is paved or 

 cement walks are laid inside the curb ? 



6. Why does the filling in of wooded land with a 3 or 4 foot layer of soil kill 



trees? 

 6. What flood-plain trees will continue to live in an area that is flooded with 



water for a year or more, as by the building of a dam? Why? Why do 



other trees die? 



