1 86 PHYSIOLOGY OF NUTRITION 



forms galactose by hydrolysis. Other hemicelluloses of the cell wall are hydro- 

 lyzed to mannose, arabinose, and xylose. The second group of cell-wall con- 

 stituents contains the true celluloses, which do not go into solution on being 

 warmed with i-per cent. acid. By hydrolysis they produce glucose only, and 

 by oxidation they give saccharic acid. 



Cellulose does not always serve only as mechanical support; in many seeds 

 thickenings of the cell walls are simply reserve materials, which are resorbed 

 during germination. 1 This reserve cellulose consists of hemicelluloses, especially 

 of mannans and galactans.' 



The cell walls of many fungi differ from those of other plants in that they 

 contain nitrogen. Those of Boletus edulis, Agaricus campestris, Morchella es~ 

 culenta, Botrytis cinerea, and Polyporus officinalis furnish illustrations of this 

 characteristic. The nitrogen content may be as great as 5.5 per cent. 2 If the 

 cell walls of such fungi are hydrolyzed by heating with hydrochloric acid, glu- 

 cosamin chlorhydrate is obtained as a decomposition product. It is represented 

 as follows: 



,COH 

 CH 2 OH— CHOH— CHOH— CHOH— CH^ 



X NH 2 — HC1 



The same substance results from the hydrolysis of the chitin of insects. The 

 cell walls of fungi thus contain substances that are very similar to chitin. 



Grape sugar (glucose) is present in many active cells, 3 and therefore merits 

 particular attention, especially since it is one of the simplest carbohydrates. 

 The structural formula of dextro-glucose, or dextrose (which, in solution, rotates 

 the plane of polarized light to the right) is as follows: 



CHO— HCOH— HOCH— HCOH— HCOH— CH 2 OH. 



Cane sugar (saccharose) was formerly considered to be of limited distribution. 

 With refinement of methods, 4 however, considerable amounts of this sugar have 

 been found in growing organs. 5 Brown and Morris 6 have identified cane sugar 

 in leaves and consider it to be the first product of the photosynthetic assimila- 

 tion of carbon dioxide." Only after the accumulation of considerable amounts of 



1 Elfert, Th., Ueber die Auflospungsweise der sekundaren Zellmembranen der Samen bei ihrer Keimung. 

 Bibliotheca botanica, Heft. 30, viii + 26 p. Stuttgart, 1894. 



2 Winterstein, E., Ueber ein stickstoffhaltiges Spaltungsproduct der Pilzcellulose. Ber. Deutsch. Chem. 

 Ges. 27 7// : 3113-3115. 1894. Idem, Ueber die Spaltungsproducte der Pilzcellulose. Ibid. 28 : 167-169. 



189S. 



3 Armstrong, E. F. The simple carbohydrates and glucosides. London, 1910. 



* Schulze, E., Ueber den Nachweis von Rohrzucker in vegetabilischen Substanzen. Landw. Versuchsst. 

 34: 408-413. 1887. Schulze, E., and Frankfurt, S., Ueber die Verbreitung des Rohrzuckers in den 

 Pflanzen, uber seine physiologische Rolle und uber losliche Kohlenhydrate, die ihn begleiten. Zeitsch. 

 physiol. Chem. 20: Si 1-555- 1895. 



* Seliwanoff, Th., Ein Beitrag zur Kenntnis der Zusammensetzung etiolierter Kartoffelkeime. Landw. 

 Versuchsst. 34: 414-417. 1887. Frankfurt, Solomon, Ueber die Zusammensetzung der Samen und der 

 etiolierten Keimpflanzen von Cannabis sativa und Helianthus annuus. Ibid. 43: 143-182. 1894. 



* Brown and Morris, 1893. [See note 1, p. 28.] 



' This sentence is omitted in the 7th Russian edition. — Ed. 



"On this point, however, see: Dixon, H. H., and Mason, T. G., The primary sugar 

 of photosynthesis. Nature 97: 160. 1916. — Ed. 



