Francis E. Lloyd — 240 — Carnivorous Plants 



This is made possible by the tight application of the door edge 

 to the threshold (specifically, to the layer of epithelium on the top 

 of the threshold) enhanced by the mucilage which has an added 

 sealing effect. Since the cells of the wall are not plasmolysed by 

 glycerin etc., water is not withdrawn from these cells but only from 

 the lumen without changes in turgor. This is what happens in na- 

 ture. The setting of the trap results from the withdrawal of water 

 from the lumen. The only agent for this is the action of the four- 

 armed hairs. It is allowed that some water may penetrate through 

 the walls inwardly but at a slower rate than that at which it is thrown 

 off, for otherwise it would lead to overtension, and this, he held, 

 would bring the trap into a condition unfavorable for prompt action. 



CzAjA holds that the withdrawal of water results not only in the 

 change in position of the walls, but that this results in turn in a 

 cramping effect on the door, forcing it against the threshold more 

 tightly and so effectively increasing its watertightness, an idea held 

 by Brocher, but which is untenable in the hght of the structure of 

 the walls, which are thin, acting as hinges near the threshold {26 — 

 3). When the trap is in the set posture, the walls concave, and the 

 door tightly in contact with the threshold, the bristles stick out at 

 an angle in such position that on touching them the edge of the door 

 is disturbed and a narrow opening is formed between the door edge 

 and the threshold, through which water is drawn in by the expanding 

 walls. The action is mechanical. In support of this Czaja records 

 that it is easier to fire the trap if the bristles are swept from above 

 downwards than transversely to this direction. This can mean only 

 that the leverage is more effective in disturbing the door edge when the 

 levers are moved in one direction than another and rules out mere irri- 

 tability. Firing the trap is due to the deformation of the door edge 

 and the consequent lifting of it from the threshold allowing water 

 pressure to act. For the rest, Czaja did much experimentation show- 

 ing that the trap is surrounded by a selectively permeable membrane 

 but Prat (1923) found that the entire plant is protected by this 

 membrane. 



Czaja was the first to take a definite stand that the trap action 

 is mechanical, aside of course from the water-extruding power of the 

 walls, and the general condition of turgidity. That is, the springing 

 of the trap is purely mechanical. This was opposed to the views 

 of Brocher, Ekambaram and Withycombe, and to Merl insofar 

 as he allowed the question to hang in the balance. Hegner (1926) 

 (not knowing of the work of Brocher, Merl or Czaja) made inde- 

 pendently the observations as to the method of catching prey re- 

 corded by Brocher, noting its rapidity, but did not venture into 

 the question of the method of function of the bristles. Thus Czaja 

 was left the sole champion of the view that the whole capturing 

 action of the trap is mechanical, but he was not to go unchallenged; 

 for Miss M. Kruck in 1931 undertook to prove the contrary, but, 

 to state it abruptly, she quite failed (Lloyd 1932&). In the first 

 place her presentation of the structure of the trap was askew and 

 it was patent from her figures that she did not grasp the anatomical 

 facts. The drawings showed initial and final positions of the door, 



