38 



PHYSIOLOGY OF NUTRITION 



bristles. When an insect alights upon the leaf and touches a bristle, the valves 

 quickly close together and a digestive fluid is secreted into the space between 

 them. 



If the ability to derive nutrition from complex organic compounds, inde- 

 pendently of photosynthesis, is a special characteristic of the insectivores, 

 nevertheless other plants that utilize the carbon dioxide of the air can also 

 assimilate complex organic substances. Green water-plants thrive especially 

 well in harbors where the water is very rich in organic compounds, in the 



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.) 



neighborhood of canals and sewer outlets; for example, the algae, Viva lactuca, 

 some species of the genera Bangia and Ceramium, and Cystoseira barbata. 

 Also, some single-celled green algae are known to grow excellently and retain 

 their green color in pure culture in darkness, with organic substances supplied. 

 Finally, it was proved by Bohm and other observers 1 that even green leaves 



1 [Boehm, Josef, Ueber Starkebildung aus Zucker. Bot. Zeitg. 41 : 33-38, 49-54- 1883. P. 35- Idem, 

 Starkebildung in den Blattern von Sedum spectabile Boreau. Bot. Centralbl. 37 : 193-201, 225-232. 1889. 

 P. 200.] Nadson, G., The formation of starch from organic substances by chlorophyll-bearing plant cells 

 [Russian]. Trav. Soc. Imp. Nat. St.-Petersbourg 20: (Sect, bot.): 73-122. 1889. 



