38 PHYSIOLOGY OF NUTRITION 



90 degrees. The free margin of each lobe is extended into sharp, slender teeth, 

 and each lobe bears on its upper surface near the center three very elastic 

 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 

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

 that have been previously deprived of starch are able to assimilate various 

 organic substances from solution and thus to form starch in darkness. In 

 this manner starch can be formed from saccharose, glucose, fructose, lactose, 

 glycerine, dextrine, mannite, melampyrite, and adonite. 2 Sapozhnikov' 5 

 investigated this matter quantitatively. Leaves of Astrapcea wallichii, 

 previously rendered starch-free, formed in seven days from 4.6 to 5.3 g. of 

 starch, per square meter of leaf surface, when floating upon a 20-per cent, solu- 

 tion of cane sugar in darkness. Here assimilation is not limited for forma- 

 tion of starch, however; the amount of proteins also increases when leaves are 

 grown upon cane-sugar solution in darkness, and respiration is accelerated. The 

 ability to absorb organic compounds is even more pronounced in roots than 

 in leaves. Many green plants possess mycorhiza (see Chapter IV) and grow 

 on humus soils, and these probably assimilate organic materials. Light 

 influences the absorption of organic compounds by green plants. 4 



According to the experiments of Reinhardt and Sushkov 5 the accumulation 

 of starch in leaves floating upon cane-sugar solution depends upon a variety of 

 conditions. This process occurs rapidly only at medium temperatures, while 

 starch that was previously present disappears at higher or lower temperatures, 

 in spite of the supply of sugar. Among poisons, some (quinin) hasten the first 

 appearance of starch but prevent its continued accumulation; others (0.5 per 

 cent, of caffein) favor the accumulation of starch. 



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-P6tersbourg 20: (Sect, bot.): 73-122. 1889. 



2 Treboux, O., Starkebildung aus Adonit im Blatte von Adonis vernalis. Ber. Deutsch. Bot. Ges. 

 27: 428-430. 1909. 



3 Saposchnikoff, W., Ueber die Grenzen der Anhaufung der Kohlenhydrate in den Blattern der Weinrebe 

 und anderer Pflanzen. (Vorlaufige Mittheilung.) Ber. Deutsch. Bot. Ges. 9: 293-300. 1891. P. 298. 

 Idem, 1890, 1893. [See note 4, p. 31.] 



1 Lubimenko, W., Influence de la lumiere sur l'assimilation des matieres organiques par les. plantes 

 vertes. Bull. Acad. Imp. Sci. St.-Petersbourg VI, 1: 395-426. 1907. 



6 Reinhard, [L. V.| and Suschkoff, Beitrage zur Starkebildung in der Pflanze. Beih. Bot. Centralbl. 

 18: 133-146. 1904-1905- 



