Francis E. Lloyd — 234 — Carnivorous Plants 



dorsal part of the entrance, its free edge hanging and in contact with 

 a firm, semicircular collar or threshold, against which the door edge 

 rests. The convex outer surface of the door bears a lot of longer 

 or shorter stalked mucilage glands, throwing off mucilage and sugar 

 (Luetzelburg), which have been said to be attractive to small animals 

 (Cyprids, Daphneae, etc.) and so to act as a lure. In addition it 

 bears four stiff, tapering bristles, based near the free, lower door 

 edge. These are the tripping mechanism. The surface of the thres- 

 hold, against which the door edge rests, is covered with a "pave- 

 ment epithelium" of glandular sessile cells secreting mucilage. Along 

 the outer edge of this pavement there is attached a thin but firm 

 transparent membrane, the velum, which lies against the lower edge 

 of the door, filling in the chink between this and the threshold. 



The internal surface of the trap carries many glandular hairs 

 {26 — 9-13), with two or four projections, the former on the inside 

 of the threshold, the latter everywhere else {26 — 2). Darwin called 

 them bifids and quadrifids. The capital cells are devoid of cuticle. 

 The rest of the surfaces except at these points is cuticularized. 



In size the traps, at their largest, are usually not more than 5 

 mm. long; in the majority of species, 3 mm. long and less. Their 

 small size has militated against readily understanding them. 



An ample, partly incorrect description of the trap was furnished 

 by Benjamin in 1848. He recalled the more important earlier ob- 

 servations: Meyen had thought the traps open in the mature plant, 

 ScHLEiDEN thought the entrance was merely guarded by hairs. 

 Treviranus realized that the tightly closed door prevents the es- 

 cape of air when inclosed within the trap. De Clair ville said that 

 the door opens outwardly, but, as Benjamin pointed out, he failed 

 to see that, if this were the case, air could escape, but nothing could 

 enter. Benjamin himself clearly demonstrated that the door opens 

 inwardly — he could push it in with a needle — but not outwardly 

 — for if you push a needle against it in this direction it is torn. The 

 function of the traps — he called them bladders — he thought to be 

 connected with the supply of air to the plant. They were to him 

 air reservoirs, getting it from the water through the four-armed hairs. 

 De Candolle (1832) and van Tieghem (1868) believed that they 

 had to do with the floating and sinking of the plant in spring and 

 autumn. As pointed out by Goebel, the plants float just as surely 

 after the bladders are removed. What had not then been observed 

 is that normally the traps hold no air, but that this enters when 

 the plant is raised out of the water. As Cohn remarked, the 

 failure to understand the traps arose out of a wrong point of view. 

 He and Darwin adopted another only in turn to prove wrong. Cohn 

 recorded finding various forms of Daphnia and Cyclops in the traps 

 of a herbarium specimen. He then put a living sprig in an aquar- 

 ium where it grew rather feebly for some time. There was no prey 

 in the traps — none in the water. He then added some Ostracods 

 from a culture, and next morning many of them had been caught 

 in the traps. But Cohn's observations did not stand alone; the 

 brothers Crouan (1858) had recorded the presence of small beasts 

 in the traps. In America, in 1873 Mrs. Mary Treat and a coworker 



