ASSIMILATION OF CARBON 



37 



dioxide from the air, which is especially true in the case of insectivorous plants.' 

 These latter are green and can assimilate carbon dioxide, but, at the same time, 

 they are provided with a characteristic mechanism for catching and digesting 

 insects (Fig. 19). In this class, for instance, belongs the widely distributed 

 sundew {Drosera rotundifolia), which grows in bogs. Its leaves are covered 

 with pin-shaped tentacles or glands, which secrete a sticky fluid. As an insect 

 alights upon the leaf the tentacles bend toward it, a copious flow of an acid liquid 



Fig. 19. — Above, a leaf of Drosera rotundifolia, whose tentacles on the .left side have 

 responded to a stimulus, and one of Nepenthes gracilis. Below, a leaf of Dionaea muscipula; 

 A, open; B, closed, with an imprisoned earwig. {After Pfeffer.) 



containing a pepsin-like enzyme takes place, and the insect is digested. Sundew 

 can also digest and absorb lean meat and white of egg. In Nepenthes ^ a part 

 of the petiole is modified into a tankard-shaped structure with the leaf-blade 

 acting as the cover. The hollow portion contains a weakly acid solution, in 

 which imprisoned insects are digested. Each leaf of Dionaea' muscipula con- 

 sists of a flattened petiole and a rounded leaf-blade divided by the midrib into 



■ Daiwin, Charles R., Insectivorous Plants. London, 187s. 



* Clautriau, G., La digestion dans les urnes de Nepejilhes. Recueil Inst. Bot. Bruxelles s : 89-133. 

 1902. Vines, S. H., The proteolytic enzyme of 2V«i)eB(A«s (III). Ann. bot. 15: 563-573- 1901. 



