THE LEAF 177 
Practical Questions 
1. Can a plant be suffocated, and if so, in what ways? (87, 193; 
Exps. 26, 27.) 
2. The roots on the palm shown in plate 3 are not drawing any sap 
from it as parasites; why does their continued growth bring about the 
death of the tree? (87, 193.) 
3. Is it unwholesome to keep flowering plants in a bedroom? Leafy 
ones? Why, in each case? (191.) 
4, Would there be any more reason for objecting to the presence of 
flowers by night than by day? Explain. (191.) 
5. Why is respiration much less marked in plants than in animals? 
(30, 31.) 
VII. THE ADJUSTMENT OF LEAVES TO EXTERNAL 
RELATIONS 
Mareriau. — A potted plant of oxalis, spotted medick, white clover, 
or other sensitive species. The subject is better suited for outdoor ob- 
servation than for laboratory work. 
ExpERIMEeNT 74. To sHOW THAT LEAVES ADJUST THEMSELVES TO 
CHANGES IN INTENSITY OF LIGHT. — Keep a healthy potted plant of oxalis, 
white clover, or spotted medick in 
your room for observation. Note 
the daily changes of position the 
leaves undergo. Sketch one as it 
appears at night and in the morning. 
In order to determine whether 
these changes are due to want of light 
or of warmth, put your plant in a dark 
closet in the middle of the day, with- 
out change of temperature. After 229 230 
several hours note results. Transfer Fias. 229, 230. — Leaves of a peanut 
to a refrigerator, or in winter place Plant: 229, in day position; 230, in 
i 2 7 night position. 
outside a window where it will be ex- 
posed to a temperature of about 5° C. (40° F.) for several hours, and see if 
any change takes place. Next put it at night in a well-lighted room and 
note the effect. If practicable, keep a specimen for several weeks in some 
place where electric lights are burning continuously all night, and watch 
the results. 
EXPERIMENT 75. To SHOW THAT THE FALL OF THE LEAF MAY RESULT 
FROM OTHER CAUSES THAN COLD OR FROST. — Wrap some leaves of ailan- 
thus, Kentucky coffee tree, ash, walnut, or hickory in a damp towel and 
