18 



pnlvini of the lateral leaflets would be perpendicular to the direc- 

 tion of light, and except that a relatively different side was 

 ilhiniinated. this was the same light relation of the lateral pnlvini 

 in the second instance. Experiments had previously shown that 

 in direct sunlight all sides of the pulvini were sensitive to light 

 and responded in the same way no matter which side happened 

 to be illuminated. If pulvini alone be considered we might have 

 expected similar responses in the two leaves mentioned above. 

 Different results, however, actually occurred. In the first leaf, a 

 twist of 90' occurred in the lateral pulvini, thus bringing the 

 blades perpendicular to the light. In the second leaf, a bend of 

 9{y occurred, accompanied at times by a slight twist. 



The terminal leaflets shifted by a bend in both instances, 

 though the illumination was one-sided in the second leaf, and 

 uniform on all sides, practically, in the first leaf. 



If, instead of the first leaf mentioned above, one had been 

 taken that was placed edgewise, though perpendicular to the 

 light, it would have been found that the terminal leaflets behaved 

 differently, though the pulvini were similarly placed respecting 

 the light, except, of course, that a relatively different part of 

 each pulvinus was illumined. 



In the first leaf a twist occurred, while in the second a bend 

 took place. It would therefore seem from these experiments 

 that the pulvini are not the organs that receive diffuse light 

 stimuli. Contraction on the illuminated side does not occur, 

 nor does there seem to be any relation between the direction of 

 light as regards the pulvini, and their response in motion. When 

 the blades are considered, however, they are found to be the 

 determining factor, since to bring their palisade surface perpen- 

 dicular to and toward the light, or so that this side will receive 

 more light than the other, is the object of all movements in 

 ditt'use daylight. When this has been accomplished, motion due 

 to paratonic stimulus ceases, no matter what the relation of the 

 pulvinus to the light may be. 



The response in motion to intense sunlight is more quickly at- 

 tained than the respcmse to diffuse light. One reason has already 

 been assigned for this, and that is the greater intensity of the 

 stimulus. Another factor should be considered, however, as there 

 is a difference in distance between the light stimulated cells and 



