430 THE FOOD OF PLANTS 



innocuous, and may be present in the plant in greater abundance than potassium, 

 though oats, barley, buckwheat, as well as typical saline plants, such as Salsola kali, 

 Ghtux marithna, and Psamma arenaria grow equally well in the entire absence of 

 sodium '. Wiegmann and Polstorff reduced the amount of sodium present to the 

 lowest possible minimum, but the complete absence of sodium can never be assured 

 when glass vessels are used. 



Potassium is presumably an integral constituent of protoplasm, and like 

 nitrogen and phosphorus, and also magnesium, it is relatively abundant in em- 

 bryonic tissues - ; it is also found in combination with reserve and translocatory 

 materials. It is possible that potassium may be intimately connected with the 

 formation of carbohydrates, but nothing definite can be said at present, for when 

 in the absence of potassium starch disappears from an illuminated leaf, this may 

 simply be due to the setting up of a pathological condition. Such observations do 

 not necessarily indicate that potassium is especially concerned in the translocation 

 of carbohydrates as Liebig and Nobbe supposed. Bearing in mind the intimate 

 correlation existing between different functions, it is not surprising that Nobbe found 

 an excessive accumulation of starch in the leaves of plants of buckwheat, which 

 grow but slowly owing to the presence of an excess of potassium sulphate and 

 phosphate, nor that a similar result should be observed in other abnormal nutrient 

 fluids or under special cultural conditions ^ 



Potassium is often present in supra-minimal amount, chiefly in the form of 

 oxalates, nitrates, &c. It is improbable, however, that potassium salts are in- 

 dispensable for the maintenance of turgidity in primary meristem, and owing to 

 their solubility they are very thoroughly removed from dying tissues, as also are 

 those of sodium. 



Chlorine. A little chlorine is present in all plants, and not merely 

 typical saline plants but many others have also a tendency to accumulate 

 large quantities of metallic chlorides 4 . All plants, however, grow normally 

 when the amount of chlorine present is very much reduced by the absence 

 of sodium chloride, but probably no plant has as yet been grown in 

 the entire absence of chlorine, and since its removal from a water-culture 



plants, see Focke, Bot. Zeitung, 1873, p. 94. Rb has also been found in plants growing in the open. 

 Both Rb and Cs are absorbed in large amount when present in the soil or nutrient solution. 



1 Cf. Nobbe, Versuchsst., 1863, Bd. v, p. 133, and 1870, Bd. xin, p. 384; Birner u. Lucanus, 

 ibid., 1866, Bd. vin, p. 165; G. Wolff, ibid., 1868, Bd. x, p. 371; de Gassincourt, Journ. d. 

 Pharmacie, 1818, p. 381 ; Wiegmann u. Polstorff, Uber die anorg. Bestandtheile d. Pflanzen, 1842, 

 p. 42. Cf. also Hoffmann, Bot. Zeitung, 1877, p. 294; Weigelt, Ber. liber d. Verh. d. Sachs. Ges. d. 

 \Viss. zu Leipzig, 1869, Bd. xxi, p. 19. 



- First observed by de Saussure, Rech. chim., 1804, p. 285. Cf. also Schimper, Bot. Zeitung, 

 1888, p. 102, and Flora, 1890, pp. 227, 261. 



3 Liebig, Die Chemie in ihrer Anwend. zur Agric., 1876, 9. Anfl., p. 97 ; Nobbe, Versuchsst., 

 1870, Bd. xin, p. 321 ; Schimper, I.e., 1890, p. 247. Cf. Brasch u. Rabe, Bot. Jahresb., 1876, p. 

 889 ; Knop u. Dworzak, Ber. d. Sachs. Ges. d. Wiss. zu Leipzig, 1875, p. 53 ; Liipke, Landw. Jahrb., 

 1888, Bd. xvii, p. 912. 



4 Cf. Wolffs Ash Analyses, 1. c. ; also Mangin, Compt. rend., 1883, T. xcvi. p. So, and the 

 literature quoted in Sect. 73. 



