256 MOVEMENT IN PLANTS. 



caused by changes in temperature in nature, of course, 

 increased light is usually accompanied by rise of tempera- 

 ture and diminished light by fall of temperature. 



Some flowers respond especially to changes in tem- 

 perature (e.g. Tulip and Crocus) ; others only, or especially, 

 to changes in light ; others again only when light and 

 temperature are altered at the same time. 



361. Temperature Effects in Tulip and Crocus 

 Flowers. Use pot plants, or cut flowers set in bottles of 

 water. In the morning bring a closed flower from outside, 

 or from a cold place indoors at about 10 or 12 C., into a 

 warm room at about 20 C., and note that the flower soon 

 begins to open. Some Tulip plants were kept at 12 C. 

 from 5 p.m. until about noon next day, and then transferred 

 to 18 C. ; during the first hour the flowers opened, but 

 during the second they closed again (owing to autotropism). 



362. After-effects of Temperature Changes. Take 

 a closed Tulip or Crocus flower in the morning and with 

 seccotine or shellac fix a thin piece of wood to the middle 

 of the outer side of (a) one of the outer perianth segments, 

 (6) the opposite inner segment, so that 2 or 3 cm. of the 

 stick projects above the flower. Fix a scale horizontally in 

 such a way that the distance between the tips of the two 

 pointers can be read on the scale. 



On bringing the plant into a warmer place (say from 

 12 to 20 C.), in about five minutes the movements of the 

 pointers against the scale show the beginning of the open- 

 ing movement. Eeplace the flower in a temperature of 

 about 12 ; it continues for a time to open, and then begins 

 to close. Before closing is complete, bring the flower once 

 more into the higher temperature, and note that it continues 

 for a time to close, and then begins to open. 



363. Opening and Closing of Composite Flower- 

 heads. Various Compositae may be used for experiments 

 on the opening and closing movements of floral leaves. Cut 

 off a Daisy with the flower-head open, fix it in a bottle of 

 water, and place it in darkness. Note the time required 



