THE BLADDERS IN UTRICULARIA VULGARIS. 409 
THE VALVE. 
It has been shown that Brocher’s theory of valve action cannot be accepted, 
as the valve can only be released by an upward movement from its groove 
(fig. 5, g) in the collar zone. 
Merl’s theory of a labile equilibrium between valve and tension within 
bladder can also not be accepted, as the pressure required to force open the 
valve of a sensitive bladder is relatively considerable. On the other hand, 
the slightest touch of the sensory hairs causes immediate response Merl 
states that he found the bladders too sensitive for observation under high 
powers. This I have not experienced. As long as the sensory hairs are not 
touched there 1s no response. 
The following method for observation of the valve was generally successful 
A sensitive (concave) bladder was selected upon a plant, its footstalk was 
severed, and while still under water it was floated into a small salt-spoon. 
This was then lifted out full of water, and transferred to an excavated 
glass block containing water. The bladder was then adjusted to stand with 
valve uppermost between supports, and the water contained in the excavated 
glass block was pipetted off to a convenient level, but not low enough to 
bring the sensory hairs into contact with the surface film of water. 
For testing the valve a piece of human hair was inserted into a handle and 
eut off short, allowing about one-eighth of an inch free. This short and 
comparatively stout piece of hair was then pushed against various parts of 
the valve, using for observation a Watson Greenough dissecting binocular 
with 27 mm. objectives and oculars number 3 or 6. It was found that the 
valve woull nowhere yield to pressure except at the lower margin of the 
valve, where pressure frequently caused the hair to slip into the bladder 
between the collar and the valve, thus of course “firing” the bladder. 
Rough friction or pressure of the club-shaped hairs covering the valve and 
rim produced not the slightest response. The only hairs sensitive to stimulus 
were the four tapering sensory hairs on the valve. 
The valve is so sprung that it always returns to its position with some 
force, even after being pushed open ventrally several times. The shortest 
time of recovery of sensitivity that I have observed is thirty minutes, and 
this I considered a distinct record. Merl gives fifteen minutes as the shortest 
time. Recovery is retarded by low temperature, but other factors are also 
involved, and in my own experiments a regular time-temperature relation has 
not been obtained. 
As regards the nature of objects touching the sensory hairs to cause 
response, these must be either solid bodies or the like. Contact with the 
surface film of water is often sufficient to ** fire" a bladder. Some liquids 
will also irritate the sensory hairs, but such appear to be injurious. — Bouin's 
Picro-formol, used as fixative, can be added to a watch-glass containing 
sensitive bladders in water without causing these to “fire,” and by very 
