CH. VIIl] DAISY, LIGHT. 221 



(253) Light and darkness: Bellis. 



Among the flowers which close in darkness and open 

 when illuminated the daisy (Bellis perennis) is the most 

 universally accessible 1 . 



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 315. 



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. repens. 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 

 outside of the rim so as to make sure that light is 

 excluded. After one or at most two hours the plants 

 may be examined, when the leaflets will be found in the 

 nyctitropic position shown in fig. 40, where the left-hand 

 leaf is awake, the one on the right asleep: the lateral 

 leaflets are face to face and the terminal leaflet folded on 



1 Pfeffer, Physiologische Untersuchungen, p. 198. 



