172 
Redfern. — On the Absorption of Ions 
The hydrogen-ibn concentration was determined by the colorimetric 
method for all solutions in which plants of Zea Mats had been growing. 
With two exceptions, the P H of the solutions remained 7-3, the same as that 
of the original solution ; in the two exceptional cases the solutions were 
slightly more alkaline, having a P H of approximately 8*o. 
The fact that the solutions remained approximately neutral, in spite 
of the more rapid absorption of calcium than chloride, suggested that other 
metallic ions might have diffused out from the roots, to replace the calcium. 
Accordingly, qualitative tests were made, and it was found that potassium 
and magnesium were present in appreciable quantity in the external 
solutions. The replacement of part of the excess of calcium ions absorbed, 
by the much more mobile potassium ions, might be sufficient to account for 
the slight increase in electrical conductivity of the external solution recorded 
in Table III. 
Discussion. 
(a) Unequal absorption of ions. The results given above show that the 
two ions of calcium chloride are absorbed at different rates by the roots of 
young plants of pea and maize. The percentage absorption of calcium 
is considerably in excess of the percentage absorption of chloride throughout 
the experiments. Thus the conclusion reached by Pantanelli, as regards 
the unequal absorption of ions, is confirmed by these results. It is note- 
worthy that the kation is absorbed more rapidly than the anion throughout 
the experiments. Pantanelli’s results show a higher absorption of the anion, 
except in the case of sulphates, and in experiments with Elodea ; the latter 
absorbed kations more rapidly than anions when chlorides were used. 
Pantanelli, however, did not use peas, though he used closely related species 
in his experiments ( Phaseolus midtiflorus , Vida faba, Lupinus albns). 
The difference in the rate of absorption of the two ions is very much 
lessened in more dilute solutions, and when the concentration is as low as 
N 
this difference is hardly outside the range of experimental error. In 
1000 
this case the results fall into line with those obtained by Hoagland ( 2 ). 
The results of the experiments on the hydrogen-ion concentration of 
the solutions in which maize plants had been grown show that the Ph 
remains approximately the same as that of the original solution (Ph = 7-3) 
in spite of the more rapid absorption of calcium than chloride. Hence the 
excess of calcium absorbed is not accompanied by hydroxyl ions in its 
entrance into the roots. Further experiments show that potassium and 
magnesium diffused out from the roots, and presumably they take the 
place, in the external solution, of the excess of calcium absorbed. 
( b ) Course of absorption. The results obtained in these experiments 
seem, at first sight, to indicate a slight periodicity in absorption, as described 
