458 SENSITIVENESS TO LIGHT. CHAP. IX. 



After 8 h. 40 m. the chords of their arcs were deflected 

 from the perpendicular by an average angle of only 

 16. Had the light been bright, they would have 

 become much more curved in between 1 and 2 h. 

 Several trials were made with seedlings placed at 

 various distances from a small lamp in a dark room ; 

 but we will give only one trial. Six pots were placed 

 at distances of 2, 4, 8, 12, 16, and 20 feet from the 

 lamp, before which they were left for 4 h. As light 

 decreases in a geometrical ratio, the seedlings in the 

 2nd pot received -\ih, those in the 3rd pot -^ik, 

 those in the 4th -jVth, those in the 5th F Vth, and those 

 in the 6th -r^-th of the light received by the seedlings in 

 the first or nearest pot. Therefore it might have been 

 expected that there would have been an immense differ- 

 ence in the degree of their heliotropic curvature in the 

 several pots ; and there was a well-marked difference 

 between those which stood nearest and furthest from 

 the lamp, but the difference in each successive pair of 

 pots was extremely small. In order to avoid prejudice, 

 we asked three persons, who knew nothing about the 

 experiment, to arrange the pots in order according to 

 the degree of curvature of the cotyledons. The first 

 person arranged them in proper order, but doubted 

 long between the 12 feet and 16 feet pots ; yet these 

 two received light in the proportion of 36 to 64. The 

 second person also arranged them properly, but 

 doubted between the 8 feet and 12 feet pots, which 

 received light in the proportion of 16 to 36. The 

 third person arranged them in wrong order, and 

 doubted about four of the pots. This evidence shows 

 conclusively how little the curvature of the seedlings 

 differed in the successive pots, in comparison with the 

 great difference in the amount of light which they 

 received; and it should be noted that there was no 



