CHAP. VIII. HELIOTROPISM. 429 



After having seen hove the epicotyls moved towards a mode- 

 rately bright light, seedlings were placed at 7.48 A.M. (Sept. 7th) 

 before a north-east window, covered by a towel, and shortly 

 afterwards by an ordinary linen blind, but the epicotyls still 

 moved towards the window. At 9.13 A.M. two additional muslin 

 blinds were suspended, so that the seedlings received very little 

 more light from the window than from the interior of the room. 

 The sky varied in brightness, and the seedlings occasionally 



Fig. 175. 



Tropaolum majus : heliotropic movement and circumnutation of the epicotyl 

 of a young seedling towards a dull lateral light, traced on a horizontal 

 glass from 7.48 A.M. to 10.40 P.M. Figure reduced to one-half of the 

 original scale. 



received for a short time less light from the window than from 

 the opposite side (as ascertained by the shadow cast), and then 

 one of the blinds was temporarily removed. In the evening 

 the blinds were taken away, one by one. The course pursued 

 by an epicotyl under these circumstances is shown in Fig. 175. 

 During the whole day, until 6.45 P M., it plainly bowed itself 

 towards the light ; and the tip moved over a considerable space. 

 After 6.45 P.M. it moved backwards, or from the window, till 



