THE LEAF 



177 



Practical Questions 



1. Can a plant be suffocated, and if so, in what ways? (87, 193; 

 Exps. 26, 27.) 



2. The i-oots 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 anunals? 

 (30, 31.) 



VII. 



THE ADJUSTMENT OF LEAVES TO EXTERNAL 

 RELATIONS 



Material. — 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. 



Experiment 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 

 several hours note results. Transfer 

 to a refrigerator, or in winter place 

 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 leavcs of ailan- 

 thus, Kentucky coffee tree, ash, walnut, or hickory in a damp towel and 



Figs. 229, 230. — Leaves of a peanut 

 plant : 229, in day position ; 230, in 

 night position. 



