Francis E. Lloyd — 204 — Carnivorous Plants 



sure of which must be overcome. As in the case of Utricularia, the 

 energy expended is sufficient to cause a trap lying free in the water 

 to close with a sudden jerk, displacing it, just as a Peclen swims. 

 There seems to be a slight difference in the behavior of the two lobes, 

 the free-side lobe moving a bit more rapidly than the other. The 

 difference is very httle, however. 



Advance from the shut to the narrowed posture is slower, more 

 irregular, complicated by conditions. The slowness depends in the 

 first place on the slowness of the mechanism causing it, namely the 

 absorption of water and extension by growth of the outer epidermis. 

 It seems not unlikely, however, that closure is impeded by the pre- 

 vention of the escape of water by the mutually appressed valves of 

 the lobe margins and the probably tight appression of the non- valvular 

 portions. This, of course, insures in nature the retention of prey. 

 To test this point, Ashida made a hole in the bristle-side lobe to 

 allow the free escape of water, when the record indicated that the 

 inclosed water in an uninjured trap does indeed offer impedance to 

 narrowing. The free-side lobe, however, due to its measurable rigidity 

 offers resistance to buckling and by itself produces irregularities in 

 the rate of narrowing, which commences in any event, if the stim- 

 ulus is sufficient, in about 30 min. after the shut stage has 

 been reached. The narrowed condition in the case of strong stimu- 

 lation, but in the absence of prey, is maintained for a period of from 

 6 to 12 hours. 



In the return to the widely open condition, the trap passes through 

 the reverse of the two phases of movement seen during shutting and 

 narrowing, that is, during a first period the rebulging of the free-side 

 lobe takes place, followed by the reopening of both lobes when the 

 trap is again ready to react if stimulation is applied. All this is 

 ascribed to the growth of the inner epidermis. During its progress 

 irregularities of rate of movement can be ascribed to the resistance 

 to the inflow of water into the narrowed trap and the elastic action 

 of the thin regions added to the action proper to the thick regions. 

 It is not known just how the water enters, but it may again be sug- 

 gested that the valve-free parts of the lips of the thin regions may be 

 the place of entrance, as well as of exit. 



To recapitulate. — The rapid shutting movement is caused by the 

 response of the inner epidermis of the thick region in loss of turgidity. 

 The slow narrowing movement is brought about by the growth of the 

 outer epidermis, following its stretching in the curving of the lobe. 

 The movements of recovery are due to the growth of the inner epi- 

 dermis, following the restoration of turgidity. The shutting move- 

 ment is facihtated by the circumstance that the walls of the outer 

 epidermis are at open rest, not stretched to their full capacity, and 

 that these walls can be stretched plastically. A feature peculiar to 

 Aldrovanda is the fact that the loss of turgor by the inner epidermis 

 causes curvature of the single large celled middle layer, the walls 

 attached to the inner epidermis shrinking and those to the outer 

 expanding. In a more anatomically complex organ, such as the trap 

 of Dionaea, the same must be true of all the parenchyma, but the 

 difference of extension between the outer and inner walls of any 



