THE ABSORPTION OF IONS BY LIVING AND DEAD ROOTS 
H. V. Johnson 
It is a well-known fact that roots often produce an acid or an alka- 
line reaction in solutions of neutral salts. ^ This might be ascribed to 
the excretion of acid or alkali by the root or it might be explained on 
the ground that the root takes up from the solution more kations 
than anions (making the solution acid) or an excess of anions (making 
the solution alkaline). 
If the root excretes acid or alkali we should expect to find these 
substances given off in distilled water. A number of investigators 
have reported that distilled water in which roots are placed frequently 
becomes acid.^ 
The writer has confirmed this and has found that after thorough 
boiling (to drive off CO2) the reaction may still be acid to litmus. In 
these experiments the writer employed roots of corn and took care 
not to allow the seeds to come into contact with the solution. 
The execretion of alkali by roots may be considered doubtful, 
although the excretion of alkali by algae has been reported. 
The amount of acidity and alkalinity produced by roots in solutions 
of neutral salts seems in many cases too great to be accounted for by 
excretion and it is presum^ably due to the absorption by the roots of 
anions or of kations. It is evident that if this is the usual method of 
absorption it deserves careful investigation. Little attention has so 
far been paid to the mechanism of this process. It is evident that 
kations can not be absorbed without anions (or vice versa) for this 
process would soon be stopped by the resulting electric stresses. It 
has therefore been suggested that an exchange of ions occurs, the plant 
giving up a kation for each kation it absorbs, and vice versa. It has 
1 Cf. J. F. Breazeale and J. A. LeClerc, U. S. Dept. Agric. Bur. Chem. Bull. 149; 
E. J. Russell, Soil Conditions and Plant Growth, p. 119; R. Meurer, Brings. Jahrb. 
Wiss. Bot. 46: 503. 1909; and the literature cited in these articles. 
2 Cf. F. Czapek, Biochemie der Pflanzen 2: 873. 1905; J. Stocklasa und A. 
Ernst, Brings. Jahrb. Wiss. Bot. 46: 73. 1908; R. Meurer, ibid. 46: 503. 1909; 
T. Pfeiffer und E. Blanck, Landw. Versuchsst. 77: 217. 1912, and the literature 
cited in these articles. 
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