30 PHYSIOLOGY OF NUTRITION 



verted into a sugar-like substance in the presence of calcium and barium 

 hydroxides. 



Reinke is of the opinion that the hydrate of carbonic acid and not the 

 anhydride, is decomposed in the light, as indicated by the equation, H 2 C0 3 = 

 CH 2 + O2. The same author 1 was successful in showing that substances 

 possessing aldehyde characters generally occur in green plants, and Curtius 

 and Reinke 2 succeeded in isolating a material of this sort and in identifying it 

 chemically. Curtius and Franzen 3 isolated a-/3-hexylene-aldehyde from the 

 leaves of Carpinus (horn-beam). This aldehyde shows the same carbon 

 skeleton as does glucose, as becomes evident from a comparison of their struc- 

 tural formulae: 



CH 3 — CH 2 — CH 2 — CH— CH— Cf (a-0-Hexylene-aldehyde) 



\H 



CHo— CH— CH— CH— CH— Cf (d-glucose). 

 I I I I I X H 



OH OH OH OH OH 

 Pollacci 4 found, furthermore, that the green parts of plants gave a positive 

 aldehyde reaction with Schiff 's reagent only if they had been previously exposed 

 to light and carbon dioxide ; if the plants had previously been deprived of both 

 light and this gas they gave, as did also fungi, no reaction for aldehyde. 8 



Formaldehyde can be utilized by green plants in the formation of carbohy- 

 drates, but none is absorbed in darkness. 5 



Walther Lob's 6 interesting researches have furnished experimental evidence 

 in favor of Baeyer's hypothesis. He used a silent electric discharge as source 

 of energy, instead of sunlight, and established the following principal reactions 

 between carbon dioxide and water, etc. 



1. 2 C0 2 = 2 CO + 2 



2. CO + H 2 = C0 2 + H 2 



3. H 2 + CO = H 2 CO 



4. CO + H 2 = HCOOH 



5. 3 2 = 20 d 



6. 2 H 2 + 2O3 = 2 H»0 2 + 2 



1 Reinke, J., Studien uber das Protoplasma. I— III. Untersuch. Bot. Lab. Gottingen 2 : 1-202. i88r. 

 Idem, Studien uber das Protoplasma. 2te Folge. Ibid. 3: 1-76. 1883. 



2 Curtius, Theodor, and Reinke, J., Die fluchtige, reducirende Substanz der griinen Pflanzentheile. Ber. 

 Deutsch. Bot. Ges. 15: 201—210. 1897. 



3 Curtius, Theodor, and Franzen, Hartwig, Aldehyde aus grunen Pflanzenteilen. I. Mitteilung. Ueber 

 a-0-Hexylenaldehyd. Sitzungsber. (math.-naturw. Kl.) Heidelberg. Akad. Wiss. Jahrgang 1910, Abhandl. 

 20. 13 p. IQIO. 



« Pollacci, Gino, Intorno all' assimilazione clorofilliana delle plante. Atti 1st. Bot. Univ. Pavia //, 

 7: 1-21. 1902. On the synthesis of carbohydrates in chloroplasts see: Fischer, Emil, Synthesen in der 

 Zuckergruppe. II. Ber. Deutsch. Chem. Ges. 27 111 : 3189-3232. 1894. P« 3 2 3°- 



5 Grafe, Viktor, Untersuchungen uber das Verhalten gruner Pflanzen zu gasformigen Formaldehyd. II. 

 Ber. Deutsch. Bot. Ges. 29: 10-26. 191 1. Idem, Die biochemische Seite der Kohlensaure-Assimila- 

 tion durch die grune Pflanze. Biochem. Zeitsch. 32: 114-129. 1911. [Baker, Sarah M., Quantitative 

 experiments on the effect of formaldehyde upon living plants. Ann. bot. 27: 411-442. 1913.] 



6 Lob, Walther, Zur Kenntnis der Assimilation der Kohlensaure. Landw. Jahrb. 35 : 541-378. 1906. 



* On reactions for identifying formaldehyde in plant parts, see Haas and Hill, 1921. [See 

 note 3, p. 6.] — Ed. 



