38 PHYSIOLOGY OF NUTRITION 



halves, like the valves of an open mussel, separated by an angle of from 60 to 

 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' 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.^ Sapozhnikov^ 

 investigated this matter quantitatively. Leaves of Astrapma wallichn, 

 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 to the 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 in- 

 fluences the absorption of organic compounds by green. plants.* 



According to the experiments of Reinhardt and Sushkov^ 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 highe^r or lower temperatures, 

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



1 [Boehm, Josef, Ueber SUrkebildung aus Zucker, Bot. Zeitg. 41 : 33-38, 49-34. 1883. P. 35. Idem. 

 St&rkebildung in den Slattern von Sedum spectabile Boreau. Bot. Centralbl. 37: 193-201, 225-232. 1889 

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

 [Russian]. Trav. Soc. Imp. Nat. St.-P6tersbourg 20: (Sect, bot.): 73-122. 1889. 



s Treboux, O., Stftrkebildung aus Adonit im Blatte von Adonis vernalis. Ber. Deutsch. Bot. Ges. 

 27: 428-430. 1909. 



' SaposchnikotE, W., Ueber die Grenzen der Anhautung der Kohlenhydrate in den blattern der Weinrebe 

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

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



» Lubimenko, W., Influence de la lumi^re sur I'assimilation des matiSres organiques par les. plantes 

 vertes. Bull. Acad. Imp. Sci. St.-P6tersbourg FJ, i : 395-426. 1907. 



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

 18! 133-146. 1904-1905. 



