FUNCTION OF THE BLADDERS IN UTRICULARTA VULGARIS. 401 
On the Function of the Bladders in Utricularia vulgaris L. By €. L. 
Wrruycomss, Ph.D., DLC. (Communicated by J. ltAMSBOTTOM, 
O.B.E., See. L.8.) 
(With 11 Text-figures.) 
‘Read 29th November, 1923. | 
Ix 1916 (8) I published a short note on the function of the bladders of 
Utricularia, showing that these were not passive traps, as was generally con- 
sidered to be the case, but. that they captured prey by active movement in 
response to stimulus. A bladder became sensitive to contact after its walls 
had become concave on each side. Then, on touching certain short hairs at 
the mouth of the bladder, the lateral walls sprang outwards, becoming some- 
what convex and so drawing a current of water into the bladder, which swept 
with it, of course, any body sufficiently light to be sucked in. 
These observations were made under some difficulties, and a hand-lens was 
my only aid to vision. Thus I would excuse a certain crudeness and 
inaccuracy of detail in this paper. As soon as a fresh opportunity offered, 
observations were recommenced and material was obtained for a more 
complete paper, with the intention of publishing a full account of the mode 
of action of the bladders, from the results of a number of experiments. 
In 1922, however, a paper by Merl (6) appeared, and Mr. J. Ramsbottom 
kindly drew my attention to this when the writing of my projected paper had 
already been commenced. From Merl’s account I learned that Brocher (2) 
had published a paper in the ‘Annales de Biologie lacustre’ in 1911, and 
had essentially discovered the mode of action of the Utricularia bladder, so 
that to him belongs the credit for first discovering the true nature of the 
bladders. Brocher (2) put forward a theory to explain the mechanism of 
the bladder, and suggested that, when-sensitive, a negative pressure obtained 
within. In this sensitive condition the valve closing the mouth of the 
bladder bulged eonvexedly outwards and fitted the orifice to make it quite 
watertight. On stimulus he suggested that the valve straightened itself, 
ceasing to remain convex, so that it no longer fitted the mouth of the bladder 
so completely. An influx of water immediately occurred, carrying with it 
any victim near at hand. l 
With Brocher’s suggestions I found my own observations mainly in agree- 
ment—that is to say, his theory of negative pressure seemed to be borne 
out by my own experiments ; but I do not think that his interpretation of the 
valve action is correct. This is certainly difficuit to observe, and Brocher 
himself says that he only puts forward his suggestion as a tentative 
hypothesis, 
