170 



PHYSIOLOGY OF NUTRITION 



carbon dioxide formed. Korsakova' has shown that lipoids likewise influence 

 the activity of proteolytic enzymes. 



Among the phosphatides, phytin^ is especially noteworthy; it probably 

 represents the first product in the assimilation of phosphoric acid. 



§9. Carbohydrates. — The carbohydrates cellulose and starch are especially 

 widely distributed in plants. Anatomical observation shows that the growth 

 of cell walls and the formation of starch grains occur only iii the immediate 

 presence of protoplasm or leucoplasts. Starch and cellulose thus appear tb be 

 transformation products of proteins.' Physiological studies also support this 

 supposition. The formation of starch and cellulose is accompanied by a de- 

 composition of proteins, whereby nitrogenous compounds, especially asparagin, 

 are formed. Thus, for example, the experiments of Hungerbiihler* upon ripen- 

 ing potatoes gave the following results, which show that starch formation is ac- 

 companied by spUtting of proteins and a formation of nitrogenous decomposition 

 products. 



On theoretical grounds Palladin^ supposes that the formation of cell walls 

 and of starch grains is accompanied by oxygen absorption, a supposition that 

 is supported by anatomical observations. 



Starch, which is insoluble in water, acts as a reserve material, the cells 

 being frequently quite filled with it. If this reserve material were stored as 

 water-soluble compounds (such as glucose), the cell walls would not then be 

 able to withstand the enormous osmotic pressures that would develop. 



The cell wall was long considered as made up of a single substance and as 

 having a simple structure, but it was later shown that it is complex. Schulze' 

 has classified the cell-wall constituents into two groups. The fijst group in- 

 cludes hemicelluloses, which can be extracted by heating in a i-per cent, solu- 

 tion of hydrochloric or sulphuric acid. Among these substances is paragalactan, 

 which is insoluble in water and is transformed by oxidation into mucic acid; it 



> Korsakow, Maiie, Ueber den Einfluss der ZelUipoide auf die Autolyse der Weizenkeime. Biochem. 

 Zeitsch, 38: 121-126. igio. 



' Vorbrodt, 1910. [See note 2, p. ISO.] 



" Langstein, Leo, Die Bildung von Kohlehydraten aus Eiweiss. Ergeb. Physiol, i : 63-109. 190a. 



' HungerbUhler, J., Zor Kenntniss der Zusammensetzung nioht ausgereifter KartoffelknoUen. Landw. 

 Versuchsst. 32 : 381-388. 1886. 



» Palladin, W., Kohlehydrate aU Oxydationsproduote der Eiweissstoffe. Ber. Deutsch. Bot. Ges. 7! 

 126-130. 1889. 



• Schulze, E., Steiger, E., and MaxweU, W„ Zur Chemie der Pflanzenzellmembrane n. (I. Abhandlung.) 

 Zeitsch. physiol. Chem. 14: 227-273. 1890. Schulze, E., Zur Chemie der pflanzlichen Zellmembranen. 

 (II. Abhandlung.) /i-id. 16: 387-438. 1892. Idem, Zur Chemie der pflanzlichen Zellmembranen. (III. 

 Abhandlung.) Ibid. 19: 38-69. 1894. 



