4 Hooker: Physiological observations 



atmosphere, without being fed with insects. They lost all traces 

 of pigment. Six of these were fed with small flies and two days 

 later pigment was observed in the marginal tentacles of the 

 youngest leaves, that had just unrolled. A similar reappearance 

 of color was observed in three other plants which caught insects. 

 This is the opposite of the results obtained by F. Darwin ('08, 

 p. 23) and by Busgen ('83, p. 592), who found that plants fed with 

 insects had much greener leaves than those which relied solely on 

 photosynthesis for their nourishment. The contradiction may 

 be owing to different environmental conditions, such as the 

 chemical composition of the substrate, the intensity of the light, 

 or the humidity of the atmosphere. The question merits further 

 investigation. 



4. Habit 



Another peculiarity observed in plants cultivated in a moist 

 atmosphere was the peculiar habit assumed by the plant. The 

 internodes became lengthened, and this was the case with plants 

 exposed either to the diffuse light of the laboratory or to direct sun- 

 light. Plants exposed to dry air were observed to retain the rosette 

 habit under both light conditions. This shows that the rosette 

 habit characteristic of D. rotundifolia is dependent upon transpira- 

 tion and not upon light, as Diels ('06, p. 32) suggests. This rela- 

 tion represents an interesting adaptation, for as long as the plant is 

 beneath the surface, the internodes lengthen, since transpiration 

 is reduced to a minimum. In this way the terminal bud is brought 

 to the surface, where rapid transpiration from the exposed leaves 

 causes the development of a rosette. 



5. Parasites 

 A great many of the plants cultivated in the laboratory were 

 destroyed by larvae accidentally brought with the material from 

 the swamp. They were larvae of one of the cut-leaf moths or 

 noctuids. Since the adult form has not been obtained, it has 

 been as yet impossible to identify them. The young larvae are 

 about a quarter of an inch long and very pale. They climb up 

 the under side of the leaf-petioles and eat the blade from behind. 

 In this way they avoid the tentacles which could easily catch and 

 digest such small creatures. The larvae select the youngest 



