THE FUNCTIONS OF THE ESSENTIAL ELEMENTS 433 



are (Pfeffer) 1 . It is moreover probable that the plant is able to regulate the 

 production of oxalic acid according to the amount required to decompose salts of 

 calcium or of other metals, as is indeed actually the case in fungi 2 . If it were 

 found possible to induce a formation of calcium oxalate in plants from which it 

 is normally absent by supplying them with an excess of calcium, the precipitation 

 of calcium oxalate would be clearly only an accidental phenomenon. In Mesembry- 

 anthemum a formation of free oxalic acid does actually occur, but ceases before it 

 accumulates to an injurious extent. 



Whatever part calcium plays, its absence may indirectly affect one or all of 

 the vital activities. Hence it is impossible to make any logical deductions as to 

 its direct functional importance from the effects its absence^ produces upon the 

 translocation of proteids or carbohydrates, or upon the growth of the cell-wall 3 ; 

 nor can any conclusion be drawn from the fact that calcium may enter in combina- 

 tion with proieids or carbohydrates, for the same thing may also take place in 

 plants to which it is not essential. 



If it is true that calcium may be absent from primary meristem and from young 

 organs, then it is evident that it is not essential for vital activity in general, but 

 only for certain special processes. Schimper was unable by micro-chemical tests 

 to detect any calcium in young shoots of Tradescantia Selloi which had developed 

 normally in its absence, but it is possible that a trace might have been derived by 

 such young organs from the older parts of the plant. In other cases, however, 

 calcium is certainly not essential, and hence Loew's hypotheses as to the part it 

 plays in the vital mechanism no longer have any general importance 4 . 



In nature, calcium is widely distributed, and hence the plant probably always 

 has a sufficient supply at its disposal, so that it involves no disadvantage when, as 

 is often the case, the seed contains less calcium than is necessary for the utilization 

 of all the reserve material. In such cases the addition of a calcium salt may 

 favour development 5 , while in others even a trifling amount may exercise a distinctly 

 injurious effect 6 . 



1 Schimper, Flora, 1890, p. 246. Cf. also Groom, Annals of Botany, 1896. p. 95 ; Kohl, 1. c., 

 p. 64. 



* Cf. Sects. 85 and 86; also Sect. 71 for connexion with proteid formation. 



3 Nobbe, Versuchsst., 1870, Bd. xill, p. 323; Raumer n. Kellermann, ibid., 1880, Bd. XXV, 

 p. 25; Liebenberg, Sitzungsb. d. Wien. Akad., 1881, Bd. LXXXIV, p. 447; Prianischnikow, Ver- 

 suchsst., 1894, Bd. XLV, p. 274. Schimper's results (Flora, 1890, p. 247) do not prove any direct 

 dependence of carbohydrate translocation upon the presence of Ca. 



4 Schimper, Flora, 1890, p. 245. Cf. Loew, Flora, 1892, pp. 368, 373; also Bot. Cenlralbl., 

 1895, Bd. LXIII, p. 161. [Loew, Bot. Centralbl., 1898, Bd. LXXIV, p. 257.] 



5 Liebenberg, I.e., p. 405; Bohm, Sitzungsb. d. Wien. Akad., 1875, Bd. LXXI, Abth. i; 

 Stohmann, Ann. d. Chem. u. Pharm., 1862, Bd. cxxi, p. 319; Prianischnikow, I.e. 



See Lidforss, Jahrb. f. wiss. Bot., 1896, Bd. XXIX, p. 36 (Pollen grains); Correns, Bot. 

 Zeitung, 1896, p. 26. 



Ff 



