Hind. — Studies in Permeability. III. 237 
substances of the cell which are responsible. The only lipoid substance 
examined, crude lecithin, gave no result similar to that obtained with living 
cells, whereas the resemblance between the action of living cells on acids 
and that of both peptone and the proteins extracted from potato is 
striking. 
Perhaps too much stress should not be laid on this isolated experiment, 
for commercial lecithin is a very impure product, and may contain as much 
as 50 per cent, impurities (8). Nevertheless, even in such a case one would 
expect a reduction in the hydrogen-ion concentration of the acid, if lecithin 
absorbed acid in the same way as the cell. 
Finally, it should be mentioned that the decrease in the hydrogen-ion 
concentration of the solutions containing plant tissue cannot be explained 
by the diffusion out from the cell of protein substances which then react 
with the acid in the external solution. Tests made for proteins in the 
external solution failed to reveal their presence there, even after forty-eight 
hours’ immersion in dilute acid. Moreover, it would be extremely unlikely 
that complex compounds like proteins would diffuse out during the first few 
hours of immersion in dilute acid. 
Summary. 
1. The hydrogen ions of all acids examined are rapidly absorbed by 
plant tissue from dilute solutions. 
2. The anion of the acid plays a large part in determining the effect of 
the acid on the cell, the fatty acids standing in strong contrast to the mineral 
acids. In the case of the mineral acids the exosmosis of electrolytes 
produced is considerably less than in the case of formic and acetic acids. 
3. Some evidence is brought forward which suggests that proteins may 
play an essential part in the absorption of acids by plants. No evidence 
has been obtained suggesting that lecithin is at all active in this regard. 
Botany Department, 
The University, Leeds. 
Literature cited, 
1. CzAPEK, F. : Versuche liber Exosmose aus Pflanzenzellen. Berichte d. dent. Bot. Ges., vot. 
xxviii, 1910, pp. 159-69. 
2. : Uber die Oberflachenspannung und den Lipoidgehalt der Plasmahaut in lebenden 
Pflanzenzellen. Berichte d. deut. Bot. Ges., vol. xxviii, 1910, pp. 480-7. 
3. : Uber eine Methode zur direkten Bestimmung der Oberflachenspannung der 
Plasmahaut von Pflanzenzellen. Jena, 1911. 
