BOTANY: A. R. HAAS 
561 
the alkali was neutralized directly to different points. Twenty-four 
hours' action on glyceryl triacetate gave the following results: 
H+ ion concentrations IQ-^ 10~^ 10"^ 10"^^ 
Activities 0.15 0.10 1.17 1.47 
Two similar experiments gave the following results: 
H"*" ion concentrations 10""'^ 10~^ 
Activities 0.91 1.68 
The action was therefore greater in slightly alkaline solution. 
1 These Proceedings, 1, 136 (1915). 
2/. Amer. Chem. Soc. (1911). 
THE EXCRETION OF ACIDS BY ROOTS 
By A. R. Haas 
LABORATORY OF PLANT PHYSIOLOGY. HARVARD UNIVERSITY 
Received by the Academy, August 28, 1916 
Whether roots excrete acid, other than carbonic, has long been a 
matter of controversy. The problem is important not only because 
acids dissolve plant food from the soil, but also because it involves the 
fundamental questions of the reaction of protoplasm and of the mechan- 
ism of secretion. 
The problem has been greatly complicated by the failure of many 
vestigators to distinguish between the effects of dead and of living 
Is. 
Becquerel early pointed out that all seedling roots when laid on 
moist neutral litmus paper possess the property of giving it a lasting red 
color, which he believed was due to excretion of acetic acid. Bous- 
singault thought that the acid might be lactic, while other investi- 
gators left the nature of the acid undetermined. The alkali salts of 
formic acid have been reported by Czapek^ in the culture solution of 
Lepidium and Hordeum seedlings. The formic acid was considered as 
coming not from the root hairs but from the sloughing off of root cap 
cells and their secondary decomposition. The drops occurring on root 
hairs in a moist atmosphere were found to give no acid reaction. The 
solvent^ action of plant roots has been considered to be due not alone 
to the respired CO2 but also to organic acids because phosphorite (which 
can be taken up to some degree by plant roots), requires a strong acid 
to dissolve it. Kunze^ believes that there is no free mineral acid in the 
root excretion of higher plants, but that the acid reaction is due to 
