EXPERIMENTS WITH FLOWERS 221 



187. EFFECT OF LIGHT 



Object. To demonstrate the effect of light on flowers. 

 Apparatus. A blooming oxalis plant. 



Method. Place the plant in the sunshine. When the 

 flowers are wide open, remove to a dark closet for one hour. 

 Bring the plant out and examine the flowers. How do they 

 differ from their original condition. 



Return the plant to the darkness and again note result. 



Repeat the experiment, using artificial light. 



Conclusion. State the effect of light on oxalis flowers. 



Suggestion. Expose night-blooming flowers, such as four- 

 o'clock, moonflower, and evening primrose, to strong light. 

 Will they respond? 



Query. Why do night-blooming flowers usually remain 

 open during cloudy days? What relation can you discover 

 between the behavior of flowers and leaves at night. 



Note. The opening and closing of flowers cannot be attrib- 

 uted wholly to presence or absence of light. There are many 

 plants which open their flowers at night. Of such are the night- 

 blooming cereus, night-blooming water lilies, evening primrose, 

 four-o'clock and moon vine. Many other plants open their flowers 

 by day and close at night. But by far the great majority of flowers, 

 when once open, remain so until fertilized. Then they wither and 

 die. 



The time of opening and closing seems rather to be a specific 

 characteristic. 



188. EFFECT OF HEAT 



Object To demonstrate the effect of change of tem- 

 perature on flowers. 



Apparatus. Flowers of crocus, tulip, or star-of-Bethlehem, and 

 a thermometer. 



