ROOTS AND THEIR RELATION TO PLANTS 33 
5. What kinds of plants would be useful in preventing the drifting 
of sand in dunes like those of figure 1? 
6. What are some reasons why embankments, as of reservoirs and 
railroad rights of way, should be kept well grassed over? 
7. Just where would you place soil fertilizers for prompt effect on 
old apple or pear trees ? 
8. Make a list of all the plants that you can find producing aérial 
roots, and try to explain their use in each case. 
9. What common plants are almost always propagated by roots? 
What ones are propagated sometimes in this way and sometimes in 
other ways? 
10. When roots are uncovered by the washing away of the soil, do 
they develop bark like that of the stem? 
