6o THE LEAF 



The protective devices of leaves are generally so apparent 

 that the student can easily make them out for himself, with 

 the help of a few suggestive questions. 



PRACTICAL QUESTIONS 



1. How can it benefit a plant to have its leaves, or some of tliem, 

 changed to tendrils? (67.) 



2. What advantage to plants is it to be able to climb? (54-57,65.) 



3. Why is it that evergreen trees and shrubs have generally eitlier 

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

 scales and needles, as in the cedar and pine? (68.) 



4. Why are winter herbs with tender foliage, like the chickweed and 

 winter cress, generally low stemmed, and disposed to keep close to the 

 earth ? 



5. Why do many plants which are deciduous — that is, shed their 

 leaves in winter — at the north, tend to become evergreen at the 

 south ? 



6. Question 5 seems to conflict with question 13, page 27 ; can you 

 reconcile them? 



7. Can you find any kind of leaf that is not preyed upon by some- 

 thing? If so, how do you account for its immunity? 



8. Make a list of some of the most striking of the protected leaves 

 of your neighborhood. 



9. What is the nature of the protective organ in each case? 



10. For protection against what does it seem to be specially adapted ? 



11. Are the plants in your list for the most part useful ones, or 

 troublesome weeds? 



12. Examine the leaves of the worst weeds that you know and see 

 if these will help in any way to account for their persistency. 



FIELD WORK 



The study of this subject and of all those that follow should be sup- 

 plemented by field work, in expeditions organized for the purpose; 

 furthermore, the student can learn a great deal for himself by keeping 

 his eyes open and observing the plants he meets with in his ordinary 

 walks. 



In connection with Sections 14-30, consider the effects upon soil 

 moisture of water transpiration from the leaves of forest trees that strike 

 their roots deep, and from those of shallow-rooted herbs and weeds that 

 draw their water supply from the surface. Consider the value of forests 

 in protecting crops from excessive evaporation by acting as wind 

 breaks. Study the effect of the fall of leaves on the formation of soil. 



