Drymoglossum is an epiphytic fern found commonly on the trunks of some local trees. It exhibits typical CAM features (Hew & Wong, 1974; Wong & Hew, 1976). It has fleshy fronds for storing water, but it is not uncommon to observe shrivelling of its fronds during dry spells. Different CAM plants seem to respond to drought differently. Under water stress, CAM plants such as Tillandsia increase their CAM activities, but plants such as Opuntia reduce their CAM activity instead (Kluge & Ting, 1978). We have reported recently that tropical succulent orchids behave just like Opuntia when placed under water stress (Fu & Hew, 1982).