a 



M ,, + -I y -' 



10:io A.M 



11;30 



5:10 



m 



d 



8:05 A.M. %-j 



l:i5 P.M. 



11:25 P.M. He 



7.40 



5:00 

 4:30 



3:30 



a 



t t " 



d 



12:30 P.M. 



1:00' 



m 



1:45 



5:15 



:05 

 9-00-11:80 A.M 



m 



n 



o 



n 



E F 



Fig. 7. ^-Z). Courses taken by tips of plumules of Indian corn (Zea mays) as 

 viewed from above in a beam of graded light (a) which was reflected from the 

 mirror m so as to illuminate the two surfaces equally. Magnified five times. The 

 arrows (a) indicate the direction of the rays from the glower, and the other arrows 

 the direction of movement of plumules; d, side of beam of light having lowest 

 intensity; /, side having highest intensity (see F below). Movement in the direc- 

 tion of the rays of light was caused by imperfect adjustment of mirror producing 

 unequal illumination from the glower and mirror. 



E, Cross section of beams of Hght. i, outline of shadow of plumule at the be- 

 ginning of Course C above, i.io p.m.; 2, shadow at 2.10 p.m.; 3, shadow at 11.25 P-M. 



F, I, shadow of plumule at beginning of Course D above, 9.00 a.m.; 2, same at 

 5.15 P.M. The light intensity at was zero; at n, about 200 ca. m. The increase 

 of intensity in the field from side to side was about 14 ca. m. per mm. It will be 

 seen that the plumules deflected strongly toward the side most highly illuminated. 



69 



