Functional Anatomy of the Oil Glands of Melaleuca alternifolia (Myrtaceae)

Abstract

The structure and development of the oil glands of Melaleuca alternifolia (Maiden & Betche) Cheel is described with reference to the production of essential oil. Oil glands were first apparent in immature leaves (ca. node 3) and continued to form, while density per unit area decreased, as the leaf expanded. The number of glands in a leaf reached a maximum prior to full leaf expansion. A genetic component related to oil gland density was indicated by a lower variation in the number of glands in the most recently fully expanded leaf within a plant than between plants of the same seed source. Oil yield was not, however, correlated with oil gland density. The cavity of the gland formed schizogenously or schizo-lysigenous. No significant variation was recorded in Be yield and composition of the oil over a 48 h period. Short term (8 day) water stress did not effect oil yield or composition. These observations are consistent with the concept of a one-way developmental pathway for oil gland formation and oil content. Varying nitrogen and phosphorus nutrition and light levels over a 3 month period did not influence oil gland density or specific oil yield from leaves formed under the imposed conditions. The effect of plant nutrition on oil production must therefore be explained by the effect on biomass production. The glands were capped by modified epidermal cells. Oil was observed to pass through these cells when the leaf was subjected to vacuum, and may allow a gradual loss of oil from the glands under field conditions.