Seasonal variation in the terpenes of the foliage of black spruce

The changes in the relative amounts of the mono- and sesquiterpenes of the volatile oil of the leaves, buds and twigs of black spruce were determined at various intervals throughout the year. Major changes take place in the young leaves just after bud burst until mid-summer. Upon maturing the same quantitative composition as that of the mature leaves is reached. The composition of the latter, as well as that of the twigs, shows only minor changes from bud burst to mid-summer and none during the rest of the year. In contrast, large relative quantitative changes take place in the bud oil throughout the year. The relative changes of santene, tricyclene, camphene, bornyl acetate and limonene in the new growth follow similar curves, but those of α-pinene, β-pinene, myrcene, car-3-ene and the sesquiterpenes differ considerably. The sesquiterpenes, and possibly myrcene, appear to be metabolized at least in part as the young leaves mature.