Chapter IV — 67 — Nepenthes 



Knoll found that if he placed an ant on a cleaned surface of an 

 iris leaf {Iris pallida), the waxy secretion thus being locally removed, 

 and then placed the leaf in a vertical position, the ant could not get 

 away from the smooth, clean part. It seems that the ant clings to 

 smooth surfaces by means of its foot-pads, not by its claws, since there 

 is no roughness available. It cannot cling to the glaucous surface of 

 the Iris leaf, however, because the waxy secretion is loose and pulls off, 

 cumbering the foot-pads so that the ant must stop to clean them be- 

 fore they are again useful. This Knoll proved experimentally by 

 seeing if an ant can walk on a smooth surface as of glass when it has 

 been coated with a thin layer of a powder such as talc or carbon and 

 found that it cannot do so. Since the ant can walk on clean glass or 

 a smooth wax surface (beeswax melted onto a glass plate) it is quite 

 evident that the difficulty for the ant lies in the particles which come 

 off on his pads and prevent him from clinging. Experiments with the 

 loose waxy covering of the iris leaf first removing it and then applying 

 it again, showed the same result. Coming to the waxy zone of most 

 Nepenthes pitchers, Bobisut had already experimented and believed 

 to have found that ants could not climb the surface when in the verti- 

 cal position; even after he had (as he thought) removed the waxy 

 surface. Believing that he had failed to remove the waxy covering 

 perfectly, Knoll continued his experiments in the same sense as be- 

 fore with Iris, etc. He removed the wax thoroughly with chloroform, 

 rubbing downwards to avoid breaking the lunate cells and produced a 

 smooth green surface showing clearly the red markings, and upon this 

 he found that the insects could climb and run in any direction. When 

 now he scattered talc powder or wax powder obtained from the pitchers 

 themselves, they failed, showing that their ability to climb on the 

 smooth surface was due to the absence of a deterrent to the use of their 

 pads. He observed, however, that ants could readily negotiate the 

 gliding zone of older pitchers in greenhouses, and thought that this is 

 due to the removal of the wax by the vigorous sprinkling with water 

 which the plants usually receive, just as rain is known to remove the 

 waxy covering from plants like Cotyledon, etc. Knoll's observations 

 on the walking behavior of ants and the effectiveness of the waxy 

 zone as a precipitating mechanism have been repeated by my friend 

 Prof. W. KuppER and myself. The plant was a vigorously growing 

 one of N. gracillima (aff.?), one which is evidently very attractive to 

 ants as they are always to be seen in numbers rapidly walking hither 

 and yon especially about the tops of the pitchers. We observed that 

 they persistently visit the lid and the rim. They run no risk of capture 

 on the lid. On the rim, however, it is supposed that they do. As a 

 matter of fact, however, they do not, for they can walk on it in any 

 direction with rapidity, and they frequently stop to take the nectar 

 from the marginal glands. They even passed underneath the rim and 

 back several times in one excursion without danger. If, however, they 

 venture on to the waxy zone they at once display a quite different 

 behavior. They cannot then by any chance move rapidly forward. 

 If they progress at all, it is very slowly and with much groping with 

 the legs as if searching for a hold. Usually this ends in a complete 

 loss of foothold, and the ant falls into the abyss. One pitcher I ex- 



