490 CONSTRUCTIVE AND DESTRUCTIVE METABOLISM 



conditions under which they have been formed crystals of different shape and 

 containing two or six molecules of water may be produced '. Anatomical facts 

 and a few theories as to the function of oxalic acid and calcium oxalate will be 

 found in the quoted works of Zopf, Schimper, Wehmer, &c. 



Acid and alkaline reactions. The sap of plants may be either acid or alkaline, 

 and the excretion of certain products of metabolism may create either an acidity 

 or alkalinity in the surrounding medium, depending upon the character of the 

 food-material supplied. Thus in the case of fungi sugar induces acidity, peptone 

 alkalinity 2 . The reaction of the cell-sap in living cells may be indicated by the 

 colour assumed by soluble pigments normally present or artificially introduced*. 

 Thus the red colour of rose petals, beet-roots, &c. shows that the cell-sap is acid, 

 the blue colouration of the hyacinth, blue-bell, or cranberry ( Vacrinium\ &c. that 

 it is neutral or slightly alkaline. Treatment with dilute acid or alkali, as the 

 case may be, may reverse the reaction without killing the cells, but after washing 

 in water the normal reaction returns again 4 . Such changes may occur spon- 

 taneously, as for example when the flowers of Pulmonaria, which are at first red, 

 become blue as they grow older. The reaction of the cell-sap is approximately 

 the same as that of the expressed sap, and in most of the higher plants this is 

 slightly sour and occasionally markedly so (Sect. 85). 



The protoplasm does not normally contain any reacting pigments & , but a feeble 

 alkalinity has been detected in certain plants by the artificial introduction of 

 methyl-orange. By means of weak organic acids this alkalinity may, however, be 

 converted into an acidity without affecting the vitality of the cell. An alkaline 

 reaction may be given with litmus solution by dead tissues rich in protoplasm 

 and by the plasmodia of Myxomycetes ', but it is possible that the protoplasm of 

 fungi may always possess an acid reaction when growing in strongly acid solutions, 

 especially when we consider the fact that many proteids (nucleins, &c.) are acid 

 compounds 7 . Certain protoplasts can, moreover, withstand strongly acid media, 

 as is the case with those plants which can grow in the presence of large quantities 

 of organic acids. 



The alkaline reaction of the protoplasm is perhaps mainly due to compounds 

 of proteids with alkalies and alkaline phosphates 8 , and these are probably non 



- 



1 See Kohl, Kalksalze u. Kieselsaure, 1889, p. 31. 



3 For examples, see Wehmer, Bot. Zeitung, 1891, p. 395; Nageli, Bot. Mitth., 1881, Bd. Ill, 

 p. 283 ; Zoller, Bot. Jahresb., 1874, p. 313; Stutzer, ibid., p. 117; Pitruschky, Centralbl. f. Bact., 

 1890, Bd. vi, p. 659; 1891, Bd. vn, p. 49 j Beyerinck, ibid., 1891, Bd. IX, p. 781 ; Timpe, ibid., 

 1893, Bd. xiv. pp. 845, &c. 



8 Pfeffer, Unters a. d. Bot. Inst. z. Tubingen, 1886, Bd. II, p. 393; telakovsky', Flora, 1892, 

 Erg.-bd., p. 233. 



4 Pfeffer, Osmot. Unters., 1877, p. 140. 



5 The occurrence of granules of chalk in the plasma affords no evidence one way or the other, 

 for these are always surrounded by an investing plasmatic membrane. 



* Sachs, Bot. Zeitung, 1862, p. 257; F. Schwarz, Beitr. z. Biol. v. Cohn, 1892, Bd. V, p. 12 ; 

 A. Meyer, Bot. Zeitung, 1890, p. 232 ; Krukenberg, Unters. a. d. Physiol. Inst. zu Heidelberg, Bd. II, 

 p. 282 ; Reinke, Studien iiber Protoplasma, 1881, p. 8. 



7 Neumeister, Physiol. Chemie, Bd. I, p. 34. 



8 Cf. Pfeffer, 1886, 1. c. ; Fr. Schwarz, 1. c., p. 32. 



