THE BLADDERS IN UTRICULARIA VULGARIS. 403 
able to test bladders with suspensions in water, as they were too sensitive to 
permit of examination under a high power. 
Admitting, then, the evidence of the majority of Merl’s experiments, but 
differing from his arguments, I will now proceed to outline my own obser- 
vations and deductions therefrom. 
DESCRIPTION OF BLADDER, 
First, to give a brief account of the bladder. It is somewhat oval in 
shape, flattened laterally, and attached by a short footstalk to an appendage 
of the plant (fig. 1). Whether the bladder represents a leaf does not concern 
us in the present discussion. The wall of the bladder is thin, usually being 
but two cells in thickness (fig. 4). The cavity is lined within with numerous 
quadrifid absorptive hairs (fig. 3, e). 
ia. 2, 
a b 
Wallis of the bladder. x 50. 
To facilitate description, the attached part of the bladder will be referred 
to as ventral, and the opposite, of course, as dorsal. The opening of the 
bladder will be termed anterior. | 
The mouth of the bladder is somewhat circular, flattened dorsally. Ven- 
trally, in a semicircle a thickened collar ensures rigidity of the rim of the 
orifice. From the dorsal part of the rim hangs down a flap, which will be 
referred to as the valve. Both terms are those previously used by Darwin (5) 
and seem well adapted to the structures in question. 
The collar is a semicircular pad of large parenchymatous celis (fig. 5, co). 
Covering this and actually forming a sharply differentiated zone round the 
inside and lower half of the mouth is a triple layer of highly-specialized cells 
(fig. 5, ul, ml, be). In surface view these cells are seen to be thicker-walled 
