Trichomes on spearmint leaf. (A) Scanning electron microscope image of spearmint leaf showing three types of trichomes, a, Non glandular hairy trichome; b, Peltate glandular trichome (PGT); c, Capitate glandular trichome. (B) Process of secretion by PGT. a, presecretory stage; b, formation of storage cavity; c, secretion into the storage cavity; d, release of oil upon injury. The PGTs were stained with toulidine blue.