K.—BOTANY 217 
is the corrugation of the periclinal walls (inner and outer). The middle 
portion of the lower half (more or less) of the door has cell courses of 
equal thickness very strongly supported by large, numerous rods. The 
cells themselves become exceedingly small, especially as they approach 
the door edge. The structure is such as to give some and equal pliability 
in either direction, combined with considerable rigidity. This is the 
part of the door which has to remain in a rigid condition to give the 
door its footing on the threshold. The extent of these parts of the 
door varies with the species and peculiarities of shape of the entrance 
structures. 
There are two general classes of trap : 
(a) Those in which the threshold is broad (from back to front), the 
outer zone bearing a broad velum, the middle zone being broad also, and 
the inner zone narrow. The door in such cases is longer than broad, and 
is so placed that when the trap is set the door edge is held in position by 
the downthrust of the lateral hinge, contributing with longitudinal thrust 
to the firm application of the door edge to a more or less upturned surface 
near the inner limit of the threshold. The angle made by the plane of 
the door with that of the threshold is a small one. The door is devoid 
of special organs for actuation, unless sessile or short trichomes scattered 
on the upper convex surface of the door may be so regarded. At all 
events, actuation follows only on the application of sufficient pressure by 
prey trying to enter to make an initial dent in the surface. ‘This allows 
the outside water to exert its pressure in folding the door lengthwise. 
The fold, travelling to the door edge, releases it from the downward 
thrust of the sides, and the door is opened. The action is by no means 
as vigorous as in the other kind presently described, nor as easily procured. 
But procured it can be, and is vigorous enough to carry in the intruding 
prey. 
(6) Those in which the threshold is narrow. The outer zone is 
relatively broad, and bears an ample velum ; the middle zone is narrow in 
the middle, widening toward the sides relatively more than in the class (a), 
and with an inner zone which is broader. The surface of application of 
the door edge is at the front of the middle zone along the middle reach ; 
along the lateral reaches the surface of the door is applied to broader, 
fan-shaped extensions of the middle zone facing outwards, procuring the 
funnel-like shape of the entrance, into which the door is cramped under 
pressure of water. Here the velum also is broader and deeper. The 
door stands at a large angle to the plane of the threshold. It is provided 
with trichomes which constitute a latch lever for the actuation of the trap. 
Contact therewith disturbs the door edge sufficiently to allow the pressure 
of water against it to become effective in opening the trap and engulfing 
the prey. 
One cannot boast that all the species fit nicely into one or the other of 
the above two categories. Beyond the general statement as made, each 
kind of trap demands its own description. One is impressed by the 
epigrammatic saying of the Italian botanist, Caruel, which was brought to 
my attention by Goebel in conversation about this very question, to wit : 
“La pianta cresce crascuna alla sua idiosyncrasia.’ 
