Chapter XIV — 237 — The Utricularia Trap 



culum" is so rapid, Brocher observed, that it closes before the walls 

 can more than partly expand, so that the trap may act again, but 

 this remained questionable. It was admitted that the contents of 

 the vesicle might be absorbed by the "rhizoids" (quadrifid hairs), 

 in which case the walls would again be drawn in, and the trap re- 

 sensitized. But Brocher, not being a botanist, was too modest to 

 undertake to solve this part of the problem. 



Ekambaram (1916, 1918, 1926) in India made observations on 

 the traps of U. flexiwsa (similar to U. vulgaris), which substantiated 

 those of Brocher above mentioned, though apparently in ignorance 

 of this author's work. That is, Ekambaram recognized the two states 

 of the trap, one with concave and one with convex sides, and that 

 in the latter, when the "irritable" hairs are touched by a prowling 

 animalcule, it is sucked into the trap with the inflowing water. It 

 had been noticed by him also that when the whole plant is lifted 

 from the water there can be heard "light crackling sounds like the 

 ticking of a watch" and this was referred to the action of the traps 

 when released, presumably by water films. When pushed in by the 

 water, the door becomes inverted and boat shaped, with the "irrita- 

 ble" hairs folded up into the groove {26 — 7). The movement of the 

 door he considered to be due to the momentary loss of turgidity, as 

 quickly regained leading to closure, but he does not offer any evidence 

 for this. The irritable hairs he mistakenly thought to have the same 

 structure as those of Aldrovanda. 



Ekambaram was able to reset the trap by carefully pressing out 

 the water by compressing its sides, but it does not appear that he 

 understood that the trap can automatically reset itself. The escape 

 from the walls of intercellular air during this operation must have 

 been accident, and can have no bearing on the matter. Merl found 

 the contrary. 



At about the same time Withycombe, a British student, announced, 

 in 1916, "that the bladders of Utricularia ... 2lXQ not passive traps, 

 but that they capture prey by active movement in response to stim- 

 ulation. A bladder becomes sensitive to contact after its walls be- 

 come concave on each side. Then, on touching certain short hairs 

 at the mouth of the bladder, the lateral walls spring outwards, be- 

 coming somewhat convex, and so drawing a current of water into the 

 bladder which swept with it, of course, any body sufficiently hght to 

 be sucked in." Again, this observation was made quite independently, 

 as Withycombe learned of Brocher's work only ca. 1922 through 

 Merl. Nor did he yet know of Ekambaram's observations. In his 

 paper of 1924 Withycombe, thinking Brocher's explanation of the 

 working of the trap valve inadequate, agreeing, however, about the 

 matter of "negative" pressure and its results, advanced the idea that 

 the edge of the valve or door, instead of being merely pressed against 

 the collar or threshold (Brocher), is caught in a groove from which 

 it can be released only by an upward movement. This groove stands 

 in front of the zone of specialized cells (see beyond) and is as deep 

 as these. "A certain amount of mucilage is secreted apparently by 

 the middle layer, and this makes a complete watertight fitting of the 

 valve." Here is a specific attempt to account for the hermetical seal- 



