234 CONTRAST. [CH. VIII 



by about 15 an opening or closing (as the case may be) 

 is produced *. 



The experiment in which the temperature is raised is 

 the only one which we have confirmed. It is simply 

 necessary to gather 3 or 4 closed daisies in the morning, 

 place their stalks in water and put the bottle near the fire 

 in a warm room : similar flowers being placed for compari- 

 son in a cool place out of doors. 



(265) Contrast: Belli*. 



If the flower-heads of the daisy or dandelion are 

 kept shut throughout the day by exposing them to a 

 temperature of 2 to 3 C. they may, according to Pfeffer, 

 be made to open in the evening by bringing them into a 

 temperature of 17 20 C. 2 



A similar experiment may be made in another way. 

 Daisies kept in the dark for two days are brought into a 

 warm and lighted room in the evening together with 

 control specimens growing under natural conditions. 

 Both sets may be gathered and placed with the stalks in 

 water. In our experiments the temperature out-of-doors 

 was 11 C., in-doors 21 C., rising to 24 C. The daisies 

 from the dark opened wide in 20 minutes. The control 

 daisies showed no opening in 20 minutes, and had hardly 

 opened after 2 hours. The degree of opening was how- 

 ever simply noted by means of rough sketches. 



1 Physiologische Unterstichuiigen, 1873, p. 195. 



2 Ibid. p. 197. 



