Chapter XIV — 241 — The Utricul aria Trap 



after stimulation and reaction, which simply do not occur. The 

 physiological evidence consisted in the observation of the extent and 

 position of intercellular spaces in the tissue of the door before and 

 after response. To meet this I reproduced photographic evidence 

 which showed clearly that such changes do not occur, though it is 

 evident that changes in the mere distribution of air might occur 

 without vitiating my evidence. Again Kruck stated that the cells 

 of the door change their shape, but this was found equally illusory. 

 In the course of response she stated that the bristles lose water, 

 supplying a stimulus to the neighboring cells of the door which re- 

 spond in like manner, with the result that the shape of the cells 

 of the door changes through loss of turgor, but evidence for this 

 was quite absent. She further allows 15 minutes for the restitution 

 of irritabihty, in this agreeing with Czaja and Merl, both of whom 

 allowed this as the time necessary for the withdrawal of sufficient 

 water to set the mechanism. If Kruck was right, it is not clear 

 why the restoration of irritabihty should not proceed when a trap 

 is punctured, but this never occurs. Most impressive is the fact shown 

 first by Ekambaram, repeated by myself, that by careful expulsion 

 of the water from a trap, it may be reset repeatedly without allow- 

 ing time for the restoration of irritability, unless, to be sure, an im- 

 mediate restoration is predicated. The claim that the bristles are 

 irritable was shown to be not true by first killing them with iodine, 

 after which they could procure response on touching (Lloyd 1932ft). 

 It should here be recalled that Withycombe observed that this re- 

 sponse could take place even in traps which had lain for a half-hour 

 in Bouin's picro-formal solution. It seems clear that Kruck failed 

 in supporting her contention. The evidence points to the contrary, 

 that the action of the door is purely mechanical, always granting 

 the turgidity of the component cells, devoid of which they could not 

 give to the door the necessary properties. 



The walls, because of their activity in excreting water from the 

 trap lumen, are an important part of the mechanism. The total 

 amount which a trap throws out amounts to 88 % according to Hegner 

 (1926), much less according to Nold. Such figures are in any event 

 not important since the total amount excreted depends on the type 

 of trap. In U. purpurea it must be much more than in U. vulgaris. 

 That they do excrete water is all we need to know to explain the 

 action of the trap, and this was first demonstrated by Brocher, 

 later independently by others, Ekambaram, Withycombe, Hegner, 

 and possibly Hada (but who had seen Hegner's paper). It may be 

 emphasized, however, that this action can go on when, as a result 

 of the introduction of much food material, including salts, in the 

 form of the bodies of water animalcules, the osmotic pressure of the 

 internal fluid reaches a considerable but never measured figure. This 

 cannot be overdone, however, for if glycerine be introduced (Merl) 

 water is then drawn into the lumen. Experiments show that the 

 trap works within wide limits in nature. Nevertheless the phys- 

 iological properties of the walls remained a subject of inquiry, and 

 this has been pursued by Czaja and by Nold. Czaja's conclusion 

 was that the trap is surrounded by a selectively-permeable mem- 



