16 BULLETIN 454, IT. S. DEPARTMENT OF AGRICULTURE. 
The percentage of esters in the oils increases as the plants approach 
maturity. The menthol content of the oil bears a close relationship 
to the ester content. The free acidity and ester content of the oil 
distilled from dry plants is considerably higher than in the oil from 
fresh plants. The drying of the plants causes changes favorable to 
esteriflcation, while the percentage of free and total menthol in oils 
distilled from dried plants is also uniformly high. 
The formation of esters and menthol takes place most readily in 
the leaves and tops of the plant, the metabolic processes showing 
increased activity as the plant matures. 
The effect of shade upon the peppermint plant is to decrease 
esteriflcation and the formation of menthol, and is due possibly to 
the lessened activity of the elimination of water by the plant. 
The action of frost noticeably increases esteriflcation and the 
formation of menthol. 
ADDITIONAL COPIES 
OF THIS PUBLICATION MAY BE PROCURED FROM 
THE SUPERINTENDENT OF DOCUMENTS 
GOVERNMENT PRINTING- OFFICE 
WASHINGTON, D. C. 
AT 
5 CENTS PER COPY 
V7 
WASHINGTON : GOVERNMENT PRINTING OFFICE: 1916 
