Chapter XII — 183 — Dionaea and Aldrovanda 



LiNDLEY (1848), like the jaws of a steel trap. The simile may not 

 be appHed too rigorously since it is not the edges of the lobes which 

 catch the prey. 



The two lobes, when the leaf is widely open, stand at an angle 

 of 40-50 (Darwin: ''80") degrees to each other, published drawings 

 being often in error on this point (iS — 40). They are clothed with 

 a distinctly firm epidermis of straight walled cells, elongated parallel 

 with the veins, becoming somewhat wavy on approaching the margins, 

 which lends a surprising stiffness to the trap. When once a lobe is 

 cut, as in making sections, it becomes evident that the epidermis is 

 the only mechanical tissue present. The outer surfaces bear scattered 

 stellate trichomes {18 — 11) which are found also in the bays between 

 the ciha of seedhng traps, and even shghtly invading their inner sur- 

 faces. The inner surfaces are supplied with very numerous glands, 

 all having the same structure. They consist of two basal epidermal 

 cells, placed parallel with the midrib, and whose walls are thickened 

 by cellulose ridges, producing an appearance which led Macfarlane 

 (1892) to take them to be ''intercellular protoplasmic connections." 

 What he saw, it seems, are only layers of cytoplasm lying between 

 the cellulose ridges, but this is not to deny that such protoplasmic 

 connections may not also be present. Surmounting the two basal 

 cells is a second course of two small cells, with cutinized diametrical 

 wall, constituting the stalk. This supports a large capital of about 

 32 cells in two courses, the lower capped by the upper to form a bun- 

 shaped mass (iS — 12, 13). There are two physiological kinds of 

 these glands, as evidence adduced by Frank Morton Jones indicates 

 (1923), namely digestive (and absorptive) and alluring. The former, 

 thought by Ellis "perhaps" to discharge a sweet liquor, occupy the 

 major area of the surface and are so numerous that they often crowd 

 on each other {18 — i). The alluring glands occupy a narrow zone 

 just within the ciHated margin. Between the two groups of glands 

 there is a narrow zone quite free of glands (Jones). Though identical 

 in structure, the digestive and alluring glands display some differences. 

 The digestive glands {18 — 12, 13) are rendered conspicuous by their 

 deep red color, due to anthocyanin present in the sap of their cells, 

 and are responsible for the deep red note of color of the inner surface 

 of the trap. The alluring glands (in the traps I examined) contain 

 no pigment. These are imbedded somewhat in the epidermis {18 — 

 14), while the digestive glands stand out prominently. These also 

 are larger (0.096-0.1 mm. in diam.) than the alluring glands, which 

 measure 0.06-0.073 mm. in diameter. That the alluring glands se- 

 crete a sugar (or something attractive to insects) is supported strongly 

 by Jones' observations already alluded to: "... these little ants 

 were observed to occupy a uniform position on the upper surface, 

 their heads close to the bases of the marginal spikes. As they moved 

 slowly across this belt of the leaf they made frequent and prolonged 

 pauses, during which their mouth parts were observed under the lens 

 to be in motion against the surface of the leaf. A larger and winged 

 hymenopteron was observed to be engaged in the same performance. 

 Obviously they were feeding upon some attractive exudation of the 

 leaf. The behavior of visiting insects is entirely convincing to the 



