Abstract
Experiments were performed in 1955 and 1956 to investigate the changes of principal oil components of mint plant during growing period. Results of the experiments are as follows. 1) Free menthol content increased with growth in the 1st and the 3rd harvesting period, but in the 2nd period it attained a maximum in early July, and no remarkable increase is recognized if the plant is allowed to stand. 2) Menthone content decreased conversely against the growth in the 1 st and the 3 rd harvesting period, but it was not distinguished in the 2nd period. 3) As whole plant including the fallen leaves, the amount of oil continued to increase until near the end of blooming, Therefore decrease of oil yield in delayed harvesting is probably caused mainly by the leaf-fall. 4) Loss of oil may occured by the rust disease. 5) Amount of free menthol and ester menthol continued to increase with growth in a whole plant including fallen leaves, but amount of menthone decreased at the beginning of blooming. Then it can be assamed that menthone is transformed into menthol by reduction in later growing stage. But in early stage menthone may be derived from menthol, because percentage of menthol in oil decreases accompanying with increase in menthone content. A possible scheme showing biogenetic relationship between menthol and menthone is shown in Fig. 6. 6) The amount of ester menthol changed almost similarly to free menthol, and the amount of unsaturated ketone to menthone. 7) Although menthone content of flower was considerably high but it exerts no influence on the total menthone content in oil because of its small quantity.
