Small-scale GC headspace analyses combined with SPME sampling of individual oil glands have been used to measure the variation in volatile content and composition in and within different oregano plants as affected by age, season and developmental state. The main monoterpenes found were p-cymene, carvacrol and their precursor gamma-terpinene. The early season preponderance of p-cymene over carvacrol was reversed as the season progressed and this pattern could also be seen at any time within the plant, from the latest leaves to be produced (low in cymene) to the earliest (high in cymene). Seedlings from the same mother plant developed this pattern at different rates. Within individual leaves the pattern was not observed, even within the youngest developing leaves. However it was found that the oil composition of individual glands within a single leaf varied considerably, most notably in respect of the production of carvacrol and its isomer thymol.

The essential oil of Lamiaceae is produced in oil glands on the leaf epidermis and stored in a subcuticular space of these specialized leaf structures. An interesting approach to better understand the variability of the essential oil composition within a plant is the analysis of individual oil glands, which is demonstrated here in the case of an accession of Satureja hortensis L. from Syria. Oil glands from different positions on the plant (petals, calyces, young, medium and old leaves) were analyzed by sampling the content of each oil gland with an SPME fiber. The main compounds identified were γ γ γ γ γ-terpinene and carvacrol, responsible for the major part (approximately 90%) of the total essential oil composition. The portion of carvacrol was highest in the petals (85%). The calyces showed intermediate values of 75% while carvacrol was equal (58%) at all three ages of leaves (young, medium and old leaves). γ γ γ γ γ-Terpinene increased from 9% in the calyx to 30% in the leaves. The lanceolate leaves were divided into four sections starting from the base (sector no. 1) to the top (sector no. 4) of the leaf blade. The content of carvacrol increased from 56% in sector no. 1 to 66% in sector no. 2 and decreased subsequently to 53% in sector no. 4. γ γ γ γ γ -Terpinene showed the opposite trend with a decrease from 32% (sector no. 1) to 25% (sector no. 2) and a steady increase to 36% in sector no. 4.