ON Drosera rotundifolia 21 



In all cases of direct stimulation of the gland, the bending of 

 Drosera tentacles is nastic; the inflected gland always points 

 toward the center of the leaf. The stimulus may be contact, 

 heat, injury or some chemical substance in solution. 



When a tentacle reacts to a single stimulation, it begins to 

 unbend immediately after the ultimate degree of inflexion has 

 been reached. This is the case when the gland has been irritated 

 by contact with some object for a limited space of time. If the 

 source of stimulation is not removed, as for example when an 

 insect is caught and digested, the tentacle remains inflected for a 

 period varying from one to eleven days, according to C. Darwin 

 ('08, pp. II, 195). During the interval between bending and 

 unbending the tentacle does not grow in length. 



ii. Unbending 



The unbending of the tentacle is accompanied by an increase 

 in the rate of growth on the concave side and in the median section. 

 The convex side always contracts so that the so-called neutral 

 line exists somewhere between it and the middle of the tentacle. 

 The acceleration of the rate of growth is characterized by a trans- 

 verse distribution which is exactly opposite that accompanying 

 bending. Its longitudinal distribution is however identical. The 

 increase in the rate of growth commences opposite that basal 

 portion of the convex side which reacted first, and extends as far 

 apically. Growth is most rapid near the base and becomes less 

 intense toward the gland. The contraction of the convex side 

 is usually restricted to a short basal region. 



It frequently happens that the concave grows less than the 

 convex side, since the latter is compressed during the expansion of 

 the tentacle. The concave side may undergo a certain amount of 

 compression during the inflexion of the tentacle, so that the two 

 sides grow and contract approximately equal amounts. The 

 unbending proceeds much more slowly than the bending. 



In all probability the unbending of Drosera tentacles is auto- 

 tropic (cf. Fitting, '03, p. 612). The stimulus perceived is the 

 inequality of conditions, pressure, tissue-tension, etc., which is 

 produced on the opposite sides of the originally straight tentacle 

 by its bending. The unbending is therefore of a tropic nature, 



