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 

 hi 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 hi 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 hi tensity 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 hi the fresh condition. 



The physical and chemical properties of the respective oils were 

 determined and for comparison are presented hi 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, L£on. Becherches physiologiques sur les feuilles de>elopp£es a l'ombre et au 

 soleil. In Rev. Gen. Bot., t. 4, p. 494. 1892. 



2 Berthelot. Sur la marche generate de la vegetation; plante u^velopp^e a. l'ombre et au soleil. In 

 Compt. Rend. Acad. Sci. [Paris], t. 128, no. 3, p. 139-144. 1899. 



3 Charabot, Eugene, and Hebert, Alex. Formation des composes terpemques dans les organes chloro- 

 phylliens. In Bui. Soc. Chim. Paris, s. 3, t. 31, p. 402-409. 1904. 



4 Charabot, Eugene, and Hebert, Alex. Consommation des matieres odorantes chez la plante #tio!6e. 

 In Bui. Soc. Chim. Paris, s. 3, t. 33, p. 580-585. 1905. 



