ORGANIC ACIDS . 489 



may be compensated for, while on the other hand a dangerous accumulation 

 may be avoided when the neutralizing substances are produced in less than 

 normal amount. As a matter of fact Penicillium, when fed with peptone, I 

 would be killed by the accumulation of ammonia (Sect. 80), were it not 

 that the amount of oxalic acid produced undergoes a corresponding increase. ' 

 Similarly in the metabolism of the higher plants the quantity of bases to 

 be neutralized must certainly vary from time to time, according to the 

 extent to which the latter are employed in metabolism, while varying 

 amounts of organic acids may be utilized for the gradual release of sulphuric 

 and nitric acids from their salts by the principle of action in mass 1 . 



Oxalic add. The different organic acids may apparently replace one another 

 to a certain extent, which is, however, strictly limited by the special properties 

 of each. As regards oxalic acid, its affinities, poisonous character, feeble heat 

 of combustion, and the insolubility of its calcium salt are all points to be taken 

 into consideration. The immediately visible character of the calcium oxalate 

 crystals has caused attention to be concentrated mainly or almost entirely upon 

 oxalic acid. In the case of Phanerogams calcium oxalate is produced at certain 

 stages of development, and various experiments indicate that here also the amount 

 produced may be modified according to the external conditions. Oxalic acid seems 

 to be a necessary bye-product of metabolism both in the higher and in the lower 

 plants, while according to circumstances it may either be further decomposed or 

 retained in combined form. This decomposition of free oxalic acid seems to be 

 possible in the higher plants as well as in the lower ones, and when sufficiently 

 active no neutralization of the free acid by combination with bases may be 

 necessary. These questions may be determined empirically, and were it possible 

 experimentally to reduce the formation of oxalic acid and prevent the production 

 of calcium oxalate, this would suffice to prove that the production of oxalic acid 

 can be regulated in the higher plants, and also that the main function of calcium 

 is not to neutralize this acid (Sect. 74). 



Oxalic acid can hardly have any general importance as such, when calcium 

 oxalate accumulates, for oxalic acid itself is a very poor reserve-material, and besides 

 calcium oxalate almost always remains intact, and it is retained by dead or dying 

 leaves. Many plants produce hardly any calcium oxalate, whereas relatively 

 enormous quantities may accumulate in others, either as unavoidable products 

 of specific metabolic activities, or for the fulfilment of special purposes. It has 

 yet to be determined why soluble oxalates are present in abundance in certain 

 plants although they may be supplied with calcium salts, and why calcium oxalate 

 is often deposited in particular cells or regions which ^re not those where the oxalic 

 acid is formed. The shape of the crystals may enable conclusions to be made as to 

 the conditions existing in the cell at the time of formation, for according to the 



1 Cf. Sects. 22, 93. C. Sprengel (Die Lehre vom Diinger, 1839, p. 62) was perhaps the first to 

 regard the organic acids as affoiding a means by which the acids of sulphates and nitrates could be 

 gradually set free and utilized. 



