Abstract
Newcastelia viscida occurs in an arid region of Western Australia. The leaves have a layer of resin with terpenoid components, secreted by glandular hairs, which makes up 15 % of the mature leaf dry weight. Five types of terpene-secreting hairs are described and their development outlined. Resin is secreted beneath the cuticle of the glandular hair, which expands and breaks to release the resin. Glandular hairs at the time of secretion are characterized by a large number of osmiophilic plastids lacking internal membranes, and tubules of proliferated rough and smooth endoplasmic reticulum.