THE LEAF 189 



5. Give a reason for the difference. (169.) 



6. Why do most leaves — notably grasses — v5url their edges backward 

 in withering ? (182.) 



7. What advantage is gained by doing this ? (202.) 



8. Observe such of the following plants as are found in your neighbor- 

 hood, and report any changes of position that may take place in their 

 leaves and the causes to which such changes should be ascribed : wood 

 sorrel, mimosa, honey locust, wild senna, partridge pea, wild sensitive plant, 

 redbud, bush clover, Japan clover, Kentucky coffee tree, sensitive brier 

 (Schrankia), peanut, kidney bean. 



9. Which of the trees named below shed their leaves from base to tip 

 of the bough (centripetally), and which in the reverse order: ash, beech, 

 hazel, hornbeam, lime, willow, poplar, pear, peach, sweet gum, elm, syca- 

 more, mulberry, China tree, sumac, chinquapin ? 



10. Account for the fact that evergreen trees and shrubs have generally 

 thick, hard, and shiny leaves, like those of the holly and magnolia, or scales 

 and needles, as the cedar and pine. (203.) 



11. Why do many plants which are deciduous at the North tend to be- 

 come evergreen at the South ? (203.) 



12. Why are evergreens more abundant in cold than in warm climates ? 

 (203.) 



13. There is an apparent inconsistency between questions 11 and 12; 

 can you reconcile it ? (203.) 



14. Why is it more important to protect the south side of trees against 

 exposure to frost than the northern side? (33, 204.) 



15. Explain why peach orchards on the tops and northern slopes of ele- 

 vated areas are less liable to have their fruit destroyed by late frost than 

 those in the valleys and on the southern slopes. (33, 204.) 



VIII. MODIFIED LEAVES 



Material. — Get from a florist a potted plant of sundew, Venus's- 

 flytrap, sarracenia, or, if possible, one of all tliree, and keep in the school- 

 room for observation. The subject can be studied best in a well-stocked 

 greenhouse, if one is accessible. 



2o6. Modification and adaptation. — Modification is 

 structural adjustment, or adaptation, carried so far as to 

 obscure the original form of an organ. Its true nature, 

 however, can generally be determined by some of the tests 

 mentioned in 100. 



Examples of the modification of leaves to do the work of 



