EFFECT OF CULTURE AND CLIMATE ON PEPPERMINT OIL. 15 
the free alcohols with the elimination of water, it is possible that 
the end result of the reaction would be intensified provided there 
was some means whereby the water could be rendered incapable of 
reversing the reaction. 
According to Charabot, 1 who has investigated ester formation in 
the peppermint plant, the esterification takes place in the green 
parts of the plant as a result of " chlorophyllic evaporation" of water 
from the leaves, while the process of oxidation of menthol to men- 
thone takes place in the floral parts of the plant. It has been further 
demonstrated by Charabot and Hebert 2 that conditions which tend 
to increase the elimination of water favor the esterification in the 
plant. The addition of salt (NaCl) to the soil was shown to be fol- 
lowed by an increase in the percentage of esters in the oil. The 
probability that esterification in a plant is aided by the presence of 
an enzym with a reversible action has also been suggested. 3 
Whatever the explanation of the wide variation in the oils may 
be, it seems evident that the effect of frost upon the peppermint 
plant tends to intensify esterification. 
If esterification is favored by a reduced water content in the plant 
due to increased evaporation, as appears from the work of Charabot 
and Hebert, freezing may bring about the same result, either by 
checking the absorption of water by the plant or by removing from 
the sphere of action the water already contained in it. Also esteri- 
fication may have continued after freezing by the aid of catalytic 
agents, the resultant water being frozen as formed, thus diminishing 
the chances of a reverse action. 
Since the percentage of free menthol was slightly higher in the 
oil from the frozen plant, and as the menthol in the plant has been 
shown to be capable of oxidation to menthone, possibly another 
effect of freezing is to lessen oxidation in the plant tissues. 
CONCLUSIONS. 
Conditions of soil and climate are influential factors in the forma- 
tion of oil and its constituents in the peppermint plant. Light sandy 
or loamy soils appear to be most favorable for the production of an 
oil of high quality. 
The yield of oil distilled from fresh plants apparently decreases as 
the plant matures. B^ing the plant before distillation results in a 
considerable loss of oil. The largest proportion of oil is found in the 
leaves and flowering tops. 
i Charabot, Eugene. Recherches sur les migrations et les metamorphoses des composes terpeniques 
dans la menthe poivree. In Bui. Soc. Chim. Paris, s. 3, t. 23, p. 466-474. 1900. 
2 Charabot, Eugene, and Hebert, Alex. Chemical investigations on the vegetation of perfume-yielding 
plants. In Bui. Sci. and Indus., Roure-Bertrand Fils, s. 1, no. 5, p. 24. 1902. 
3 Charabot, Eugene, and Hebert, Alex. Recherches sur le mecanisme de l'etherification chez les 
plantes. In Bui. Sci. et Indus. Roure-Bertrand Fils, s. 1, no. 4, p. 3-16. 1901. 
