FUNCTIONAL-ANATOMY OF THE OIL GLANDS OF MELALEUCA-ALTERNIFOLIA (MYRTACEAE)

The structure and development of the oil glands of Melaleuca alternifo lia (Maiden & Betche) Cheel is described with reference to the product ion of essential oil. Oil glands were first apparent in immature leave s (ca. node 3) and continued to form, while density per unit area decr eased, as the leaf expanded. The number of glands in a leaf reached a maximum prior to full leaf expansion. A genetic component related to o il gland density was indicated by a lower variation in the number of g lands in the most recently fully expanded leaf within a plant than bet ween plants of the same seed source. Oil yield was not, however, corre lated with oil gland density. The cavity of the gland formed schizogen ously or schizo-lysigenous. No significant variation was recorded in B e yield and composition of the oil over a 48 h period. Short term (8 d ay) water stress did not effect oil yield or composition. These observ ations are consistent with the concept of a one-way developmental path way for oil gland formation and oil content. Varying nitrogen and phos phorus nutrition and light levels over a 3 month period did not influe nce oil gland density or specific oil yield from leaves formed under t he 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 pa ss through these cells when the leaf was subjected to vacuum, and may allow a gradual loss of oil from the glands under field conditions.