182 



PHYSIOLOGY OF NUTRITION 



Treub 1 has developed the hypothesis that hydrocyanic acid is an interme- 

 diate product in protein synthesis. It is well known that many leaves contain 

 appreciable amounts of hydrocyanic acid (in the form of glucosides). With 

 suitable treatment such leaves give a chemical test for this acid by becoming 

 intensely blue, with the formation of Prussian blue (Fig. 87, a). If the leaves are 

 left several days in darkness the hydrocyanic acid disappears completely as 

 is shown by the complete absence of Prussian blue after application of the test. 

 The leaf shown in Fig. 87 was divided along the midrib and one portion (a) was 

 subjected to the test, after which the remaining portion (b) was kept in the dark 

 for a time, the test being finally applied to this part also, without the formation 

 of any Prussian blue. 9 



Leaves that have thus been depleted of hydrocyanic acid again produce it in 



considerable quantity when supplied with 

 nitrate and sugar in darkness, or when supplied 

 with nitrate in light. Considerable amounts of 

 hydrocyanic acid are also contained in axial 

 organs (young bamboo sprouts). 2 



Protein decomposition occurs in germinat- 

 ing seeds in darkness, while the later stages of 

 germination in light exhibit protein synthesis. 

 In this case also, light is directly necessary only 

 for the formation of carbohydrates. Protein 

 yff\ V'V^I formation, out of carbohydrates and nitrog- 

 enous organic substances, is independent of 

 light. Leek bulbs, for instance, contain little 

 protein, but much carbohydrate and or- 

 ganic nitrogen. Consequently, according to 



Zaliesskii, 3 the sprouting of these bulbs in 

 Fig. 87. — Leaf of Phaseolus luna- \ L . . 



lus, showing coloration with Prussian darkness is not accompanied by protein de- 

 blue (a), due to presence of hydro- composition, but by its synthesis. The follow- 

 ing data referring to leek bulbs in the dormant 

 condition and after having grown for a month in darkness, may serve as an 

 illustration of this. The numbers, excepting the last two, show the relative 

 amounts of the various materials mentioned that were found in the two stages 

 of development. 



1 Treub, M., Nouvelles recherches sur le role de l'acide cyanhydrique dans les plantes vertes. Ann. 

 Jard. Bot. Buitenzorg //, 4: 86-147. 1904. Idem, same title. Ibid. II, 6: 70-114. 1907. 



2 Walther, O., Krasnosselsky, T. Maximow, N. A., and Malcewsky, W., Ueber den Blausauregehalt 

 der Bambusschoszlinge. Bull. Departement Agric. Indes Neerlandaises, No. 42. 4 p. 1910. 



3 Zaleski, W., Zur Keimung der Zweibel von Allium cepa und Eiweissbildung. (Vorlaufige Mittheil- 

 ung.) Ber. Deutsch. Bot. Ges. 16: 146-151. 1898. 



« The test for hydrocyanic acid here referred to is carried out as follows: The leaf is punched 

 full of minute holes by means of a bunch of fine needles and is then placed in 5 per cent, solu- 

 tion of potassium hydrate for a minute or two. It is then transferred to a warm (6o°C.) 

 aqueous solution of ferrous sulphate (2.5 per cent.) and ferric chloride (1 per cent.), where it 

 remains about ten minutes. It is finally placed in hydrochloric acid (1 part of ordinary con- 

 centrated acid to 5 or 6 parts of water). The color develops after from five to fifteen 

 minutes. — Ed. 



