402 DR. C. L. WITHYCOMBE ON THE FUNCTION OF 
Merl (6) made a large number of experiments upon the bladders, and 
many of his results are very similar to my own. It would therefore now 
appear superflous to give all mine in full, and only such will be mentioned as 
bear upon the mechanism of the bladder. For the effects of varying con- 
ditions, reference should be made to Merl’s paper. 
Two theories for the mode of action of the bladder were put forward by 
Merl. Both appear to me to be rather indefinitely stated, and I am not sure 
that I have followed his meaning exactly. On page 72, in summing up the 
action of the bladder, he says: “ Sicher unrichtig ist, sie mit Wachstums- 
erscheinungen oder den Druckverhältnissen der darüber lastenden Wasser 
baw. Luftmasse in Zusammenhang zu bringen.” This statement, or rather 
the latter part of it, seems to me to preclude Brocher's “ negative pressure ” 
Fra. 1. 
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theory, with which latter I would agree in principle. As alternatives Merl 
suggests, first, that the bladders exhibit irritability similar to that seen in 
Aldrovanda and Dionea ; apparently he considers the walls to bulge forcibly 
outwards on stimulation, as do the leaf-lobes of Dionwa inwards, Secondly, 
Merl says that the only possible alternative theory is that the walls ars pulled 
together by cohesion of water, and that there is a labile equilibrium between 
the pressure of the elastic valve and the pull of the walls. He seems to regard 
this last theory as the more improbable, and says, on the contrary, that bladders 
containing bubbles of air can still act in response to stimulus. He adds that 
automatic “ firing” would probably oceur with such a mechanism when the 
pull within had become too great for the valve to withstand. He was not 
