Francis E. Lloyd — 236 — Carnivorous Plants 



pressure (Cohn), or by its own property of elasticity, the latter im- 

 plicit in all Darwin's statements. It remained thus till 191 1 when 

 a Swiss entomologist, Brocher, became interested in Utricularia. 

 Pointing out that the view just above expressed is but an hypothe- 

 sis, since no one had actually observed what happened, Brocher 

 tried to do this. 



In a series of experiments (Czaja does him the injustice of say- 

 ing he did none) Brocher established the following points, to his 

 own satisfaction. When an animal is caught it always disappears 

 very suddenly. Darwin and Busgen (1888) had all seen this 

 and recorded their observations, but had drawn no correct inference 

 therefrom. Further that, at the moment of this disappearance, the 

 trap gives a spasmodic jump, and widens a little, from which Brocher 

 concluded that the trap sucks in the prey (57 — 4, 6, 9). This observa- 

 tion was of fundamental importance. He was able then to explain 

 why, when a leaf is raised out of the water, the traps are often found 

 to contain air bubbles, whereas before they were absent. On lifting 

 a plant from the water he could hear a " crepidulation" (an observa- 

 tion made independently by others) explained by the swallowing of 

 air by reacting traps. He saw that in traps which had not reacted, 

 the sides were concave, but after reaction were flattened or slightly 

 convex. Finally he found that he could cause a trap to react by 

 ''titillating" the door bristles with a needle point, and that when 

 this was accomplished there was each time a spasm of movement, 

 and a change in profile. These observations by Brocher, made with 

 exactitude, furnished a point of view which finally led to the correct 

 explanation of the workings of the trap. 



Passing on to hypothesis, he supposed that the collapsed form 

 of the trap is explained by the principle that the rate of develop- 

 ment of the tissues, being quasi superficial, is greater than the rate of 

 expansion of the volume. To the extent that the walls are depressed, 

 the tensions of their tissues are augmented and thus they try the 

 more to take a normal position, that is, to obliterate their re-entrant 

 curvatures. The walls are therefore in a position of unstable equilib- 

 rium, during which the interior is in a state of "negative", that is, 

 reduced pressure. The proof of this is the fact that, when punc- 

 tured, the walls take up the normal position, dilating to a maximum. 

 This could not be possible if the structure of the trap is as repre- 

 sented in the textbooks, he remarked at this point, since a simple 

 check valve could not preserve the reduced pressure. He further 

 supposed that the door is strongly curved, especially transversely, 

 and that, because of the curvatures of the wall, it is held firmly against 

 the lip, and, with the addition of mucilage, is thus rendered a water- 

 tight valve (Text fig. 7). In order that the equihbrium thus pre- 

 served may be upset, Brocher assumed that the door is endowed with 

 a certain "sensibility" and "contractihty", so that, on touching the 

 bristles, it can shrink a little, and thus allow the water pressure to exert 

 its force. An animal doing this would be swallowed with the inrushing 

 water. That minute fish are sometimes caught by the tail shows that 

 it is not because they try to get in, but that merely by the flick of the 

 tail, they have stimulated the trap. The action of the door or "oper- 



