Chap. IX. SENSITIVENESS TO LIGHT. 407 



ledons of Avena were also painted in the same manner^ 

 but with greater care; and they were laterally de- 

 flected from the line of the window, towards the 

 unpainted side, by the following angles, 44°, 44°, 55°, 

 51°, and 57°. This deflection of the cotyledons from 

 the window is intelligible, for the whole unpainted 

 side must have received some light, whereas the oppo- 

 site and painted side received none ; but a narrow 

 zone on the unpainted side directly in front of the 

 window will have received most light, and all the 

 hinder parts (half an oval in section) less and less light 

 in varying degrees ; and we may conclude that the 

 angle of deflection is the resultant of the action of the 

 light over the whole of the unpainted side. 



It should have been premised that painting with 

 Indian ink does not injure plants, at least within 

 several hours ; and it could injure them only by stop- 

 ping respiration. To ascertain whether injury was thus 

 soon caused, the upper halves of 8 cotyledons of Avena 

 were thickly coated with transparent matter, — 4 with 

 gum, and 4 with gelatine ; they were placed in the 

 morning before a window, and by the evening they 

 were normally bowed towards the light, although the 

 coatings now consisted of dry crusts of gum and 

 gelatine. Moreover, if the seedlings which were painted 

 longitudinally with Indian ink had been injm-ed on 

 the painted side, the opposite side would have gone 

 on growing, and they would consequently have become 

 bowed towards the painted side ; whereas the curvature 

 was always, as we have seen, in the opposite direction, 

 or towards the unpainted side which was exposed to 

 the light. We witnessed the effects of injuring longi- 

 tudinally one side of the cotyledons of Avena and 

 Phalaris; for before we knew that grease was highly 

 injurious to them, several were painted down one side 



