Chapter XIV — 239 — The Utricularia Trap 



it." Among this evidence, he found that during action there was no 

 disturbance of the air in the intercellular spaces, which would occur 

 if there was an extrusion of water into them such as occurs in irri- 

 table tissues. In spite of inimical evidence, however, Merl inclined 

 to think that the bristles are irritable hairs analogous to those of 

 Dionaea and Aldrovanda (as had Ekambaram and Brocher). He 

 proposed, however, the only alternative theory, a purely mechanical 

 one. The four-armed hairs withdraw the water from the interior 

 of the trap, thereby setting up a tension, the walls responding to 

 the draft by cohesion of the water. The highly elastic door, the free 

 edge of which rests firmly against the threshold, opposes this draft 

 and comes into a position of labile equilibrium, which must be dis- 

 turbed "by the slightest movement or by shrinkage" of the (door) 

 cells, to allow the walls to retract into their relaxed position. Even 

 now he could not quite exclude a certain irritabihty as a capstone 

 of the bridge. This view was to be championed later by Kruck. 



Working at the same time, independently of Merl, Czaja exam- 

 ined the problem of the Utricularia trap. His publication was but 

 a trifle later than Merl's. Proceeding from the same point of at- 

 tack, Czaja agreed with Merl that the trap could repeat its action, 

 and could reset itself in a short period of 15 to 30 minutes and that 

 the reaction (on suitable stimulation) takes place very suddenly. 

 The concave sides then became much less so. The door in this re- 

 action opens to a narrow slit, and closes as suddenly as it opens 

 (neither of which, however, is quite true) allowing the entrance of a 

 stream of water. The process is released by touching the bristles. 

 By chemical means Czaja could not decide definitely on the nature of 

 the mechanism, and this left him for the moment at the same point 

 as it did Merl. With respect to the anatomy of the trap, he exam- 

 ined first the closure of the trap by the door, in order to settle the 

 question of the path of the internal water when the trap is exhausted 

 as it must be when the walls pass from the less to the more concave 

 posture. He determined that the entrance is hermetically sealed. The 

 proof consisted in inserting a fine hair beneath the door edge, when 

 the trap could not again set itself. When the hair was withdrawn, 

 again the trap became effective. Further proof was supplied by the 

 fact that Congo red and methylene blue never entered healthy, but only 

 damaged, traps. All this he beHeved points to the membrane, or rather 

 the wall of the trap, as important. 



As had been demonstrated by Cohn in 1875, the walls of the trap, 

 if set free to act by removing inhibiting structures (the threshold and 

 contiguous walls), will expand. Because of their structure and the tur- 

 gidity of their cells they always strive to take an outwardly convex 

 form. Substances which can reduce their turgor (5% KNO3) put the 

 trap out of commission. On the other hand substances which cannot 

 penetrate but which withdraw the water from the trap (glycerine, 

 cane sugar) can up to a certain limit of concentration reset the trap 

 but if in too great concentrations, cause its total collapse. The reset- 

 ting of the trap is therefore the result of withdrawing water from its 

 lumen, and not of direct participation of the walls which would in- 

 volve turgor changes. 



