ABSORPTION OF IONS BY LIVING AND DEAD ROOTS 25 1 
also been pointed out that the same thing may occur in adsorption by 
various colloids.^ 
It is of course possible that the root gives off hydrogen ions only 
when it absorbs a corresponding number of other kations. In this 
case excretion of acid by the root would take place only in solutions 
of salts. In the same way hydroxyl ions might be exchanged by the 
root for other anions. 
It is evident however that all the facts can be accounted for in 
another way. The hydrolytic dissociation of neutral salts produces 
both acid and alkali and, as has been pointed out by Osterhout,^ if 
one of these is absorbed by the plant more rapidly than the other the 
solution must become acid or alkaline. 
It is evident that an exchange of ions may occur without altering 
the reaction of the solution. In such cases the exchange could be 
detected by an analysis of the solution, before and after the roots have 
acted upon it. This method has been employed by Meurer'' and 
others. 
One point which seems to have been lost sight of is that in experi- 
ments of this sort the unequal absorption of anions and kations may be 
due to the dead rather than to the living cells of the root. Thus for 
example in the extensive experiments of Meurer on beets and carrots 
the outer layers of the root were cut away by means of a knife. This 
killed the cells for some distance below the surface so that the solution 
came into contact with a large mass of dead cells before it penetrated 
to the living tissue. 
It is to be expected that this would affect the results and the 
writer's experiments show that this is the case. For example the 
writer has found that live beets removed, from a solution of CaCl2, 
41.31 per cent, of the Ca present and 43.74 per cent of CI, while dead 
beets removed of 44 per cent of Ca and only 26.25 P^i" cent of CI 
(Table I, averages). Carrots gave a similar result, the live plants 
removing 9.65 per cent of Ca and 7.8 per cent of CI while the dead 
removed 53.87 per cent of Ca and 28.57 P^r cent of CI (Table I, 
averages) . 
^ von Bemmelen, Zeitschr. Anorgcin. Chem. 23: 321, 1900; Hober, Physikal- 
ische Chemie der Zelle und der Gewebe, S. 239, 1914. 
^ Science n. ser. 36: 571. 1912. 
^ Meurer, R. Prings. Jahrb. Wiss. Bot. 46: 503. 1909. 
