Chapter XII — 185 — Dionaea and Aldrovanda 



lying the base of the lever, and stand upon a base of about four or 

 five courses of cells, meeting the general leaf surface. All the cells 

 have rather thick walls, and there are no intercellular spaces. This 

 whole basal region is the podium. Its histological character just 

 mentioned is such as to permit bending. It is, however, the whole 

 podium which bends, and not merely the cells under the constriction 

 0/ ~ 5)- I noted while cutting hand sections that the podium readily 

 stretches and compresses, bending being a combination of these. But 

 although the whole podium bends notably when the lever is much 

 displaced, it is quite clear on watching with the microscope that 

 sHght bending is evident first and at once in the constricted zone, 

 as GoEBEL recorded. 



The hinge cells were thought by Macfarlane (1892) to be de- 

 void of a cuticle, or to have a very thin one. Haberlandt, however, 

 denied this. The cuticle is fairly thick and displays a certain amount 

 of wrinkling, which would allow freer movement of the coUench}^- 

 matous cell walls beneath. It further appears finely punctate, inter- 

 preted by Macfarlane as due to the presence of pores. Haberlandt 

 regarded this to be due rather to denticulations of the inner surface 

 of the cuticle which prevent loosening of the cuticle under repeated 

 bendings by anchoring it to the cellulose wall. It is easier to agree 

 with Haberlandt that the points seen (of which there is no doubt) 

 are not pores, than that they are extensions of the cuticle into the 

 cellulose underneath. Nevertheless, it is possible to see minute ir- 

 regularities on the inner face of the cuticle, so that the interface 

 between the cuticle and cellulose is greater than it would be other- 

 wise. 



The medullary cells show some peculiarities. In addition to a 

 fime porosity (Goebel), Haberlandt records the presence of mi- 

 nute granular inclusions of high refringency in the middle layer 

 between the walls and between these and the hinge cells. He de- 

 scribes these as cutinized granules. Some cutinization certainly oc- 

 curs. 



There is no vascular connection between the medullary cells of 

 Goebel and the leaf, since there is no vein in the hair. 



The internal structure of the leaf blade or trap was described by 

 MuNK in 1876, concerned as he was with the direction of movement 

 of electrical currents, in much detail as to form and position of the 

 component cells. We recall that the trap has a massive midrib trav- 

 ersed longitudinally by a double vascular bundle which gives ofif 

 branches, running parallel to each other, towards the margins, ap- 

 proaching which they form a coarse zig-zag network. All the remain- 

 ing space between the two epiderms is occupied by a thin-walled 

 parenchyma, of large-sized cells inside and smaller against the epi- 

 derm, those against the inner epidermis being larger than those against 

 the outer, where they are much smaller and more numerous. There 

 are more smaller cells opposite the vascular bundles and more cells 

 of very large size between the vascular bundles {18 — 10). The 

 walls beneath the inner epidermis and the cells of the first parenchyma 

 course are thickened into a collenchyma {18 — 5) and to some ex- 

 tent also, those between this and the next course. This mechanical 



