Francis E. Lloyd — 202 — Carnivorous Plants 



gion of active bending is. To determine this, he devised a method 

 of imbedding the open trap in agar jelly, transferring it from warm 

 water to still fluid agar at the same temperature, low enough to do 

 no harm. On setting, the agar with its imbedded trap could be cut. 

 It was noticed that on cutting the leaf it would react, and in doing 

 so, it would withdraw from the agar on the outside, so indicating 

 the zone of maximum bending. This was found, as already shown 

 above, to be in the flanks of the thick region, between the flat part 

 next the midrib and the outer rib-like region (2, ig — 23). How 

 is this movement accomplished? In a complete response the amount 

 of movement is sufficient to bring the edges of the thick regions 

 in mutual apposition, thus inclosing an ellipsoidal shut-off space. 

 Meanwhile, as already said, the thin regions dish the one into the 

 other as the result of mutual pressure brought about by the thick 

 regions. 



Precisely what happens to procure the bending is more obscure. 

 An observation made by Ashida is, if substantiated, of prime im- 

 portance. It is that the outer epidermis of the motile zone, when 

 in the state of open rest, is undulated, and in this condition not 

 in a state of extension, whereas the inner epiderm is, if not fully ex- 

 tended, at least more so than the outer, since very hght, if any, un- 

 dulation is to be seen. During closure the undulations disappear, 

 due to stretching of the tissues. As I have already suggested (1933), 

 the two epiderms act after the fashion of a bi-metallic spring. As- 

 suming this to be the case, two questions arise. What condition 

 of the tissues operates to keep the outer epidermis lax? And what 

 happens to procure the changes from the lax to the taut condition? 



In addition to this undulation of the outer epidermis, the motile 

 region is thinner than the non-motile parts of the thick region. And 

 if the opposing lobes are cut away so as to exclude their mutual 

 pressure during closure, it is ascertained that the lobes can curve 

 far more than they do otherwise, as is the case in Dionaea; and fur- 

 ther, that the free-side lobe bends, during closure, more than the 

 bristle-side lobe. Ashida has also demonstrated to his own satis- 

 faction that the outer epidermal walls are the more easily extensible, 

 the outer subepidermal walls less easily, while the two inner walls 

 are least extensible. This conclusion is regarded as flowing from the 

 observation that, if a trap is plunged in acetone or alcohol, under 

 the internal pressures induced by the entrance of these fluids into 

 the cells, vesicles arise, but only on the outer face of the motile zone. 

 The vesiculation is caused by the rising of the cuticle and the breaking 

 of the radial walls of the epidermis. Evidently the outer epidermal 

 walls are readily extensible, but, since they do not retract when the 

 vesicles are reduced, they are thrown into folds. Ashida argues that 

 the walls are plastically, not elastically, extended. That the motile 

 zone is weaker than the lobe is elsewhere was shown by a tearing test, 

 the result being that the lobes always tear at the motile zone. Again, 

 from observing the movements of the intercellular air on the en- 

 trance of alcohol, the inference was drawn that the walls in the motile 

 region are more readily penetrated than elsewhere. 



Before discussing the mode of operation of the motile mechanism 



