CARNIVOROUS PLANTS 



139 



One of the water-plants of Southern Europe, Aldrovandia 

 vesiculosa, which is also to be found in swamps on the northern ridge 

 of the Alps, possesses, in addition to the capturing and digesting 

 apparatus proper, an active motile apparatus, which is set in motion 

 through sensitive hairs. When I found the plant for the first time 

 in a swamp at Lindau, on the Lake of Constance, I took it at first 

 sight for an Utricularia, for the two plants resemble each other 

 in external appearance (cf. Figs. 22 and 29), but the modification 

 of the leaves into traps is quite different. On both halves of the leaf- 

 blade there are numerous bristles (Fig. 30, A), and the lightest touch 

 on these hy a little water animal acts as a releasing stimulus to the 

 motile elements of the leaf (Stch). As in the Venus fly-trap, the 



Fig. 30. Aldrovandia : its trap apparatus. A, open. St, stalk 

 of the leaf. S^Jj-.bladeoftheleaf. S<c7t, sensitive bristles. Dr, glands. 

 B, closed, a cross-section. 



two halves of the leaf close together somewhat quickly, but quite 

 quietly, and the animal is caught. Fig. 30 shows a section of one 

 of these traps in its closed state. The captive animals cannot escape, 

 because the margins of the leaf shut quite tightly on one another, 

 and are beset with little teeth. Numerous little glands {Dr) secrete 

 a digestive juice, and after some days, or even weeks, the insoluble 

 remains of the minute animals may be found inside the trap. 



Many more cases of animal-catching plants might be adduced, 

 but it is far from my intention to try to describe all the existing 

 contrivances ; those already mentioned may suffice to give an idea of 

 the diversity and of the detailed effectiveness of these adaptations. 

 They amplify — so it seems to me — our conception of the scope of 

 natural selection, by showing us that adaptations may arise which 



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