Francis E. Lloyd — 184 — Carnivorous Plants 



observer that a baited area extends across the leaf surface just within 

 the bases of the marginal spines. This baited marginal band is so 

 situated upon the leaf surface that a visiting insect in length too small 

 to reach from the halt to the trigger hairs, usually does not spring the 

 trap. Whether or not these conditions are to be interpreted as ad- 

 justments to that end, the effect of the arrangement, in conjunction 

 with the peculiarities of the closing movement by which small insects 

 are given an opportunity to escape, is to limit the captures of the 

 leaves to insects approximating one quarter of an inch or more in 

 length." Jones examined the captures of fifty closed traps and found 

 that, of all the prey "only one was less than 5 mm. in length and 

 only seven less than 6 mm.; they were 10 mm. or more in length, 

 with a maximum of 30 mm." (Jones 1923). In this way was cor- 

 roborated Darwin's suspicion that the posture first assumed by the 

 trap on closure in which the marginal spines form a cage is one which 

 permits small insects to escape. I have observed larger ones, small 

 centipedes, doing their best to force their way between the spines, 

 but without success. A wood louse was seen to free itself because 

 its position was such that its carapace held the lobe margins open 

 just enough to allow escape, which was evidently facilitated by the 

 fact that the lateral projections of the carapace allowed leg movement. 

 Many a wood louse is not so lucky. 



The closure of the trap, a seismonastic movement, normally follows 

 when sensitive or trigger hairs are disturbed as Curtis recorded in 

 1834. "Each side of the leaf is a little concave on the inner side 

 where are placed three deHcate, hair-hke organs, in such an order, 

 that an insect can hardly traverse it, without interfering with one 

 of them, when the two sides suddenly collapse and enclose the prey 

 with a force which surpasses the insect's efforts to escape." Though 

 usually three in number on each lobe, there may on occasion be more 

 or fewer. When three, they stand at the angles of a triangle 

 placed in the middle of the lobe with its base nearer and parallel 

 to the outer cihated margin. If we examine one of these hairs we 

 find that it is multicellular and displays two distinct regions. The 

 outer of these is a slender cone {18 — 2) in form, about 1.5 mm. 

 in length and 0.15 mm. thick at the base. It is composed of elon- 

 gated, thick walled cells and constitutes a lever; any slight move- 

 ment causes a bending in the basal region, to which Oudemans (1859) 

 attributed a special sensitivity. This is only 0.15 mm. in height 

 and is conspicuous on account of a deep constriction slightly below 

 the base of the lever, first described by Goebel (1891). This con- 

 striction, the hinge or bending place (Goebel), is made up of a single 

 transverse ring of cells of which their outer walls are deeply indented 

 {18 — 15, 16). Their lateral walls are thick and collenchymatous in 

 character, their end walls thin. Because of the indentation, the outer 

 wall is thinner at this point. Within the ring of indented cells there 

 is a medullary group of elongated cells, tracheidal in character 

 (Goebel), absent from the small trigger hairs of seedling leaves, which 

 measure only 0.15 to 0.2 mm. in length, of which the lever occupies 

 well over a half, the greatest width being 0.03 mm. {18 — 3). The 

 indented cells are surmounted by three layers of flattish cells under- 



