CH. Vlll] DAISY, LIGHT. 203 



will have increased by 2'5 p.c, on the outer side an 

 increase of say 0'2 p.c. will be noted. If the readings are 

 taken first in the open flower and then in closed con- 

 dition, precisely the reverse is noted, namely, that the 

 inner side increases only a little, while the outer side 

 grows about ten times as much. 



(253) Light and darkness: daisy. 



Among the flowers which close in darkness and open 

 when illuminated the daisy (Bellis perermis) is the most 

 universally accessible ^ 



A daisy should be cut and fixed vertically in a bottle 

 of water, when the position of the ligulate florets must 

 be noted ; this may either be done by taking the angle 

 which the flower-head fills when looked at in profile, or by 

 measuring the horizontal distance between the tips of 

 two opposite florets. In one of our experiments a daisy 

 was darkened at 2 p.m., and the angle showed a diminu- 

 tion of 30° by 3-15. 



Further experiments on the daisy are given in the 

 next section. 



(254) Light and darkness: Trifolium. 



Sleeping plants can be made to assume the nocturnal 

 position by darkening them in the daytime. This can 

 be shown in any of the common species of clover, such 

 as T. repms. The simplest plan is to cover a plant 

 (growing in the open air) with an inverted vessel made of 

 opaque material, scattering dry powdered soil round the 



' Pfeffer, Physiologische Untersuchungen, p. 198. 



