86 BOTANY: PRINCIPLES AND PROBLEMS 



320. The leaves of "compass plants" are erect and vertical, with 

 their edges pointing approximately north and south. In what two ways 

 may this character be of advantage to the plant? 



321. Plants with downy or woolly leaves are very abundant on 

 mountain sides and exposed alpine situations. Why are they particu- 

 larly suited to such conditions? 



322. Why do epiphytes (p. 174) usually have leathery leaves? 



323. The leaves of evergreens in temperate regions are usually firm 

 and leathery. Explain. 



324. Evergreen trees often suffer from "wind burn" in late winter or 

 early spring, a part or all of their branches dying and turning brown. 

 They do not suffer from this cause earlier or later in the season. 

 Explain. 



325. Give two reasons for the fact that plants grown in the shade 

 are usually more tender than plants grown in the bright sunlight. 



326. Why is the best lettuce grown in early spring? 



327. Spring is the best season to transplant a tree. Why? 



328. Why is it better to do transplanting on a cloudy or rainy day 

 than on a bright one? 



329. Why is it advantageous to cut off the outer leaves of young 

 plants before transplanting? 



330. If it is necessary to transplant young trees during the summer, 

 the plants should first be vigorously pruned. Why? 



331. Why will potatoes in storage lose weight much faster after 

 sprouts have grown out on them? 



332. Why is it best to store apples in a fairly moist place but beans 

 where it is dry? 



333. Tobacco growers sometimes cover their plants with cheese-cloth 

 tents. What effect do you think this has on the structure and functions 

 of the tobacco leaves? 



REFERENCE PROBLEMS 



36. Give an example of a leaf which has assumed some of the functions 

 of a stem. 



37. Where is the palisade layer in leaves which stand erect, like those of 

 Iris? 



