Francis E. Lloyd — 248 — Carnivorous Plants 



We consider now the door or valve. This is a flap, two cell courses 

 in thickness, forming the upper free edge of the entrance opening, and, 

 in nature, bulges outwardly (2j — 2, 5). If it is removed by cutting 

 along its line of attachment to the trap wall and is allowed to lie in 

 water, it retains the shape it has in situ as Bijsgen observed (1888). 

 It is, if we disregard minor curvatures, roughly semicircular, the 

 shorter side being the free edge. For the sake of description we may 

 flatten the door and then map out certain regions, shown in the dia- 

 gram {2Q — 13). A wide zone around the edge of attachment is the 

 hinge region, where strong reverse flexures occur when the door is 

 opened. The middle region of this zone is the upper hinge, the two 

 lateral the lateral hinges. The upper hinge is characterised by marked 

 flexures when the door is at rest. The hinge area surrounds a lentic- 

 ular middle area, which may be called simply the middle area. At 

 the lower part of this a small circular patch of the door is quite thin, 

 and this is the central hinge. Out from just below this project four to 

 six stout, curved, tapering bristles. That part of the door below the 

 central hinge is thick and strong. This is the middle piece. Towards 

 the flanks, the door selvage becomes thinner. With this terminology 

 {26 — i) we can more easily describe the histology. 



As above said, the door consists of two cell layers {2j — 2, 5; 2g — 

 I, 2), an outer, and an inner. The two are very different in structure, 

 the general relation between them being that existing in a bimetallic 

 strip, one of the metals having a greater index of expansion than the 

 other; the former under changes of temperature is active, the latter 

 relatively passive. The cells of both layers are equally turgid, but the 

 inner is capable of ready expansion and contraction of its inner surface, 

 the outer not. This is ascribable to the differences of structure. The 

 door has been described as highly flexible and elastic, as for example 

 by Darwin. Highly flexible it is, but if by elasticity we mean ex- 

 tensibihty, this adjective does not apply. The tissue has a sort of 

 cartilaginous quality, bending without breaking in any direction. If 

 the door is freed in part by cutting a median strip, releasing this from 

 the pull of the sides, it will spring outwardly and only on plasmolysis 

 can it be brought back. This shows that the door as a whole is always 

 normally insistent in pushing outward, and is held in its proper position 

 only by virtue of its semicircular attachment to the trap wall. As 

 Benjamin showed, it can be pushed in- but not outwardly. When 

 fully inwardly inflexed, it is folded along its middle line, becomes some- 

 what concave, and the tripping bristles then lie in the groove of the 

 fold {26 — 7), as Ekambaram described it. 



The inner reaches of this attachment, that is, the lateral hinges, 

 coincide with the inner ends of the threshold, the extreme end of the 

 free door edge coinciding with the inner angle of the threshold. The 

 outer surface of the lateral hinge therefore lies against the outer reach 

 of the threshold. But the free edge of the door, starting from the 

 inner angle of the threshold, passes obliquely across it, the angle be- 

 tween the face of the door gradually changing till, in the middle reach, 

 it stands obhquely on edge {26 — 2). Only the middle reach of the 

 door selvage is thickened and stiff; the outer reaches are thin. 



The rest of the attachment extends along the wall of the trap, curving 



