Oil glands. Coloured scanning electron micrograph (SEM) of a leaf from a crested latesummer mint plant (Elsholtzia ciliata). The circular light green structures are oil glands, modified glandular hairs which secrete oils to give the plant its aroma. The smaller protrusions enclosing slits are stomata. They are pores in the leaf's epidermis through which gases and water vapour pass.