ON Drosera rotundifolia 25 



in response to impulses received by the discal tentacles and con- 

 ducted to the marginal ones. The mechanism by which these 

 reactions are carried out is identical with that described above. 

 Numerous experiments were made to determine if the marginal 

 tentacles bent toward the source of stimulation. The discal 

 tentacles on one side of a leaf were stimulated and most of the 

 marginal tentacles which reacted to the conducted impulse, in 

 bending toward the center of the leaf bent likewise in the direction 

 of the source of excitement. In a number of such cases, however, 

 marginal tentacles were observed to bend toward the center of 

 the leaf in a direction different from the point of excitement. 

 One or two instances in which the tentacles bent slightly in the 

 direction of the source of excitement and not toward the center 

 of the leaf seemed to be purely accidental and due rather to 

 irregularities in the contour of the leaf. Nitschke ('60, p. 240) 

 and C. Darwin ('08, p. 198 and fig. 10) noticed that when a gland 

 on one side of the disk was stimulated, " the surrounding tentacles" 

 bent to the point of excitement and not to the center of the leaf. 

 The statement by Darwin together with his figure has generally 

 been understood to include the marginal tentacles. He says, 

 however ('08, p. 200): "It is, perhaps, owing to the exterior 

 pedicels being much flattened that they do not bend quite so 

 accurately to the point of excitement as the more central ones." 

 I am convinced that the peripheral tentacles seldom if ever carry 

 out tropic movements. 



vii. Discal Tentacles 

 The discal tentacles differ both anatomically and physio- 

 logically from the marginal tentacles. The latter are dorsi-ventral 

 and nastic, the former are radial and tropic. The central tentacles 

 do not bend in response to a direct stimulus, but only to a con- 

 ducted impulse, and always toward the point of excitement. The 

 method used for investigating the mechanics of the movement 

 of the marginal tentacles is not adapted for studying them in the 

 central tentacles. In all probability, however, their movements 

 are likewise the result of differential growth on opposite sides. 

 The angle of curvature is in any case slight. This and the small 

 diameter of the tentacles indicate that the amount of growth is 



