Francis E. Lloyd — 246 — Carnivorous Plants 



trunk of the appendage are long uniseriate hairs. In other species 

 {U. vulgaris americana, U. oligosperma) the antennae are much smaller 

 and curve upward, away from the entrance. There are often no 

 antennae in these species, and there are others from which they are 

 always absent {U. nana) {28 — 5). In still other species, as will be 

 seen later, quite other arrangements are met with. In the water- 

 dwelling species, while they can evidently be regarded as elaboration 

 of the trapping mechanism, it must be said that their absence does not 

 seem to make any practical difference in the number of prey cap- 

 tured. In the mud dwelling species, they may serve to keep the 

 entrance free from detritus, and so help in preserving the effectiveness 

 of the trap. In the wet sandy soils and in wet moss, where the water- 

 is not continuous, such arrangements may be important in keeping 

 capillary water, in which prey may move, in contact with the entrance, 

 so that when the trap acts it does not draw in air. The capillary 

 action in such cases is helped by the mucilage secreted by glandular 

 hairs in large numbers attached to the door itself, and to the sides of 

 the entrance. 



After the two Hps are laid down during the development of the 

 trap, the sides of the entrance extend, moving the lips apart so as to 

 produce a funnel-shaped approach. These sides, called by Cohn the 

 cheeks, are continuous with the overhang, when this is present, to 

 form a sort of hood or "vestibule" around the opening {2j — 9). 



From each cheek, and from the edge of the overhang, springs an 

 oblique row of long uniseriate hairs, about four on each cheek, and two 

 or three from the overhang (27 — 7). 



It is only in the front of the opening that the hps are drawn apart. 

 At their free edges they remain close, and in the final stages of develop- 

 ment are in mutual contact. At their lateral extremities they are 

 continuous, though their anatomical character changes. Another 

 important feature is alteration in the form of the lower lip. Though 

 transverse at first, it becomes finally semicircular in shape and thick- 

 ened by the growth of additional layers of wall cells beneath it to form 

 a massive thickening and strengthening of the wall in this zone. This 

 structure so produced was called the collar by Darwin, and the abut- 

 ment by GoEBEL. In this account it is called the threshold. By its 

 form and strength it preserves the shape of the opening, and resists any 

 cramping effect (said to occur by Brocher and Czaja) of the dis- 

 tortion of the walls when the maximum of internal water has been 

 withdrawn. Measurements made by myself did not reveal any differ- 

 ence in form in the set and the extremely relaxed condition of the trap 

 after puncture. In fact, the walls where they articulate with the 

 threshold are thinner than elsewhere, so that they can bend without 

 exerting distortion on it {26 — 3), besides which is the fact that the 

 inner part of the threshold is supported free of the wall, so that this 

 cannot press upon it. 



The structure of the threshold in detail is best understood first by 

 an examination of a transverse section through its middle point (25 — 

 I, 2, 5; 2g — 4) and then by viewing it from a point of view which 

 embraces the whole inner surface, flattened out for convenience of 

 study {25 — 9) . In the transverse section the threshold is roughly 



