Alterations in essential oil gland number, distribution and fine structure,
and the oil content in the leaf of Mentha arvensis L. were examined during
its growth and senescence. Accumulation of essential oil occurred predomin
antly during the rapid leaf expansion phase followed by a similar decline.
The oil gland (trichome) number increased upto leaf maturation and declined
thereafter. Initially, cuticle remains tightly apposed to the secretory he
ad of oil glands but progressively a sub-cuticular space appears to be crea
ted for the oil. Considerable enlargement of vacuole with ageing is witness
ed, whereas cytoplasm gradually decreases to a thin peripheral layer. Some
secretory cells from senescing leaf were found almost empty, having only a
few remnant oil droplets.