EFFECT OF CULTURE AND CLIMATE ON PEPPERMINT OIL. 11 
The percentage of free menthol in the leaves and tops during the 
various stages does not seem to bear any constant relationship to the 
ester content or to the fre3 menthol content of the oil from the whole 
plant. The total menthol of leaves and tops, however, is higher in 
nearly all cases than that of the fresh herb. 
It would seem from the foregoing results that the formation of 
the principal constituents of peppermint oil, namely, menthyl acetate 
and menthol, takes place chiefly in the leaves and tops of the plants, 
beginning at an early stage of growth and increasing as the plant 
matures. 
EFFECT OF LIGHT AND SHADE. 
In a study of the effect of soil and climatic conditions upon the 
constituents of plants the factor of light is considered important by 
certain investigators. 
Geneau 1 states that strong light has a favorable effect upon the 
decomposition of carbon dioxid and the elimination of water vapor 
in plants. Berthelot 2 has observed that plants grown in the shade 
contain noticeably greater proportions of water than plants grown 
in the light. 
Charabot and Hebert 3 have investigated the peppermint plant 
and find that darkness considerably reduces the percentage of volatile 
oil in the plant. It is also stated by these investigators 4 that plants 
kept in the shade consume the terpene constituents of the oil. 
For the purpose of ascertaining the effect of shade on the yield and 
composition of peppermint oil, cultural experiments were conducted 
through two successive years upon a small plat of peppermint grown 
under a slat shade, whereby the light intensity was reduced about 
50 per cent, and upon a similar plat grown in the open to serve as a 
check. The plants were harvested during the flowering stage and 
distilled in the fresh condition. 
The physical and chemical properties of the respective oils were 
determined and for comparison are presented in Table VI. 
It will be observed that in 1910 the yield of oil was the same from 
both the shade-grown and the unshaded plants, while in 1911 the 
yield from the shade-grown plants was slightly in excess of that from 
the unshaded plants. These results are at variance with those of 
earlier investigators with respect to the formation of oil in shade- 
grown plants. The plants described were, however, grown in only 
partial shade, which may have been the optimum condition for the 
formation of the oil in 1911. 
1 Geneau de Lamarliere, Leon. Recherches physiologiques sur les feuilles de>elopp£es a 1'ombre et au 
soleil. In Rev. Gen. Bot., t. 4, p. 494. 1892. 
2 Berthelot. Sur la marche generate de la vegetation; plante u6velopp6e a 1'ombre et au soleil. In 
Compt. Rend. Acad. Sci. [Paris], 1. 128, no. 3, p. 139-144. 1899. 
s Charabot, Eugerie, and Hebert, Alex. Formation des composes terp^niques dans les organes chloro- 
phylliens. In Bui. Soc. Chim. Paris, s. 3, t. 31, p. 402-409. 1904. 
4 Charabot, Eugene, and Hubert, Alex. Consommation des matieres odorantes chez la plante £tiol<Se. 
In Bui. Soc. Chim. Paris, s. 3, t. 33, p. 580-585. 1905. 
