PLANTS WHICH EXHIBIT MOVEMENTS IN THE CAPTURE OF PREY. 151 



the larger live articulated animals — earwigs, millipedes, and dragon-flies — caught 

 upon the upper surface of the leaf, cause the lobes to slam together, they are able 

 to slip out if part of their bodies projects beyond the toothed margin, for the teeth 

 are flexible and yield to strong pressure. But small creatures are hopelessly lost 

 when the lobes have closed over them. They are at once suffocated in the liquid 

 which is poured out copiously by the glands and are then dissolved and absorbed 

 with the exception of their claws, leg-bones, chitinous rings, &c, which are incapable 

 of being digested. 



In spite of the identity of aim and of result, the mechanism of a Dioncea leaf 

 differs very materially from that of the sun-dew leaf described above. Division of 

 labour is carried much further in the Fly-trap. The pre-eminently sensitive 

 structures, viz., the six filaments situated upon the upper surface of the leaf, 



Fig. 29. — Aldrovandia vesiculosa. 



do not act also as digestive glands. Again, the long sharp teeth at the edge 

 of the leaf, which correspond in position to the marginal tentacles of a sun-dew leaf, 

 carry no glands, and only serve to close the trap securely when an animal has been 

 caught. Accordingly in Dioncea there exist special structures for three different 

 functions, namely, stimulation, seizure, and digestion, whilst in the case of Drbsera 

 all these functions belong to the gland-bearing tentacles alone. The stimulus acting 

 on the sensitive filaments on the leaf of the Fly-trap is liberated in the form of a 

 rapid motion of the lobes and a discharge of digestive fluid from the glands, and 

 this discharge of secretion ensues therefore through the mediation of cells which 

 have not themselves been directly excited. The process here again is much more 

 striking than in the sun-dew leaf. The transmission of stimulus, though as a fact 

 identical in the two plants we are comparing, proceeds at any rate with much 

 greater rapidity in Dioncea than in Drosera. 



The analogy existing between these processes, especially the conduction and 

 liberation of stimulus, and similar phenomena of the muscles and nerves in an 

 animal organism, has already been brought out in discussing the sun-dew. It is a 

 noteworthy fact that, in the fly-traps, actual electric currents have been observed, 

 which shows that the greatest resemblance exists to muscles and nerves as regards 

 electro-motor action also. A positive current runs from the base to the apex of the 

 lamina; another current running in the opposite direction is demonstrable in the 

 petiole; and the upper layers of cells in the lamina and the midrib are ascertained 



