Chapter XIV — 259 — The Utricularia Trap 



From that point as seen along the sagittal line, the door is gently 

 concave throughout its whole length. The whole extent of the middle 

 piece is covered by the velum {24 — 6), leaving the upper region with 

 the tripping hairs exposed. A touch on this surface discharges the 

 mechanism, and the door immediately returns to the closed but now 

 relaxed posture in which the whole door is convex outwardly. In the 

 set posture, while concave along its middle axial line, it is slightly 

 convex transversely, that is, it is saddle-shaped. It was possible to 

 make transverse sections of the hving trap, and these disclosed the 

 door posture in the middle piece region, from which it was clearly seen 

 that the close application of its selvage to the pavement is procured by 

 the thrust of the thick lateral hinges. The release from this posi- 

 tion results only from the longitudinal extension of the shallow fold 

 already present in the set posture of the door. 



ScHiMPER (1882) was the only previous student of this plant. 

 Since he accepted the Cohn and Darwin view, he was not aware of 

 any special significance to be attached to the structures of the entrance 

 mechanism. 



U. caerulea {31 — i), U. ogtnospenna, U. equiseticaulis, U. bifida 

 (Asia), U. cyanea (Australia) and a lot more species, with the general 

 features of the trap very similar, conform to U. cornuta, except in 

 relatively unimportant details. They are usually provided with two 

 simple antennae and a small overhang, and the tripping mechanism 

 consists of a group of short-stalked glandular hairs, the longer nearer 

 the top of the door, and the shorter as the middle piece is approached. 

 Goebel's very brief account of the trap of caertdea shows the general 

 position of the door correctly though sketchily. U. bifida is evidently 

 of this group (Goebel) as I have myself determined, confirming 

 Goebel's drawing as correct. Only bifid hairs are present in the 

 interior of the trap, as Darwin observed. In such species, however, the 

 glands below and at the edge of the threshold have a single capital. 



As a type of the second sub-group, we choose U. capensis, and 

 U. Welwitschii. A number of other species pecuhar to S. America, 

 Central and South Africa, all small plants, fully conform to this type. 

 A description of the form of the door and of its manner of operating 

 has already been given above (p. 255). The tripping mechanism (jz — 

 8, 9) consists of a curiously formed large trichome, the capital cell 

 of which resembles in shape a Malay kriss, called therefore the kriss 

 trichome (Lloyd 1931), supplemented by a group of curved glandular 

 hairs on the upper part of the door. In some species the kriss trichome 

 is not present, its place taken by large globular sessile glandular cells 

 {U. pellata, U. Deightonii Ms.) {31 — 6, 7). A conspicuous feature of 

 this group of plants is the development of a funnel shaped approach 

 to the entrance by spreading of the cheeks, and the lining of this 

 funnel with about ten rows of stout glandular hairs radiating towards 

 the entrance. In U. Welwitschii these are reduced to mere sessile 

 glands but a rostrum bears a radiating row of longer glandular hairs 

 {31 — 4). The S. American U. peltata, so like U. capensis except for 

 the globular tripping hairs, has in common with some African species 

 (£/. Deightonii in Ms.) minute peltate leaves very thickly covered with 

 stiff mucilage (29 — 9, 10), a significant fact of geographical distri- 



