1896] CURRENT LITERATURE 509 
uncommon occurrence. It diffuses from living cells in the youngest part of 
the root and is therefore not a product of destructive processes. 
The detection of oxalic acid as primary potassium oxalate is at present 
limited to the excretions of the root of Hyacinthus orientalis. 
The well known permanent reddening of litmus paper depends as a rule 
upon the acid reaction of mono-potassium phosphate. Its intensity varies, 
and these differences are parallel with the amount of phosphate excreted. 
The acid reaction of the hyacinth roots to litmus paper has, on the contrary, 
another source, which js referable to the primary oxalate. 
f the phenomena of the corrosion of stone plates by roots are studied by 
using artificially prepared plates consisting of substances of known solubility 
in certain acids, it becomes evident that the carbonic acid excreted must play 
the principal rdle in all the etching observed. One may say in general that 
substances which cannot be dissolved by carbonic acid cannot be attacked to 
any extent by the root excretions, so that corrosive action does not appear. 
It is to be observed that we have to deal not with the action of carbonic acid 
in free gaseous condition, but with the solvent actions of fluid saturated with 
carbonic acid, as the water of imbibition of the outer layers of the membrane 
of the root cells and the adjacent films of the soil water. Moreover, all 
4 known phenomena of corrosion can be completely explained by the action of 
+ carbonic acid. Hence it results that the reddening of litmus and the corrosion 
4 _ of stones depend upon the action not of the same but of two different sub- 
stances (mono-potassium phosphate and carbonic acid). No other free acid 
is secreted, normally at least, by roots. Acid action upon the substratum by 
substances secreted by roots, however, is probable from a series of empirically 
established facts, and it occurs, asa matter of fact, without relation to the 
ects produced by carbonic acid. The mono-potassium phosphate excreted 
Senin 
neutral salt shall not be readily taken up and consumed by the plant, but may 
enter in more or less undiminished amount into reaction with the phosphate. 
aturally the amounts of acids thus formed are very small, yet they are 
Sufficient in a long period of time to produce noteworthy effects in large 
Masses of soil thoroughly permeated by roots, by means of which its insoluble 
‘Constituents are unlocked and made available to plants. 
__ Anexcretion of diastatic or inverting enzymes by the roots is physiolog- 
ically not inconceivable, but certainly does not occur normally. Critical 
Tepetition of the researches of Molisch, who has asserted a normal occurrence 
Of these ferments in root secretions, shows instead a negative result when one 
Arelully considers the sources of error.—C. R. B. 
