160 SENSITIVENESS TO LIGHT. Chap. ES. 



in the curvature of the seedlings in the two pots. 

 After 2 h. 12 m. the chords of the arcs of four of 

 the most strongly curved seedlings in each pot wero 

 measured, and the mean angle from the perpendicular 

 of those which had previously been kept in darkness 

 was 19°, and of those which had previously been illu- 

 minated only 7°. Nor did this difference diminish 

 during two additional hours. As a check, the seed- 

 lings in both pots were then placed in complete dark- 

 ness for two hours, in order that apogeotropism should 

 act on them; and those in the one pot which were 

 little curved became in this time almost completely 

 upright, whilst the more curved ones in the other pot 

 still remained plainly curved. 



Two days afterwards the experiment was repeated, 

 with the sole difference that even less light was 

 admitted through the window, as it was protected by a 

 linen and muslin blind and by two towels ; the sky, 

 moreover, was somewhat less bright. The result was 

 the same as before, excepting that everything occurred 

 rather slower. The seedlings which had been pre- 

 viously kept in darkness were not in the least curved 

 after 54 m., but were so after 70 m. Those which had 

 previously been illuminated were not at all affected 

 until 130 m. had elapsed, and then only slightly. 

 After 145 m. some of the seedlings in this latter pot 

 were certainly curved towards the light ; and there 

 was now a plain difference between the two pots. After 

 3 h. 45 m. the chords of the arcs of 3 seedlings in 

 each pot were measured, and the mean angle from the 

 perpendicular was 16° for those in the pot which had 

 previously been kept in darkness, and only 5° for 

 those which had previously been illuminated. 



The curvature of the cotyledons of Phalaris towards 

 a lateral light is therefore certainly influenced by the 



