The youngest shoot (approx. 10 mm) gave the best
result in proliferation of shoots in terms of both percentage
(100) and number of shoots (10) formed from single shoot
(Table 1). Multiple shoot formation decreased as cultured
single shoot were longer or larger. The shoots larger than
30 mm (in height) failed to develop multiple shoots. Many
orchid species require auxins and/or cytokinins for induction
of both shoot and protocorm-like bodies (PLBs). The ratio of
those plant growth regulators for development of those
organs depends on the species (Arditti and Ernst, 1993). For
in vitro regeneration of R. gigantea via PLBs, NAA at 0.1 mg/
l was first reported by Vajarabhaya and Vajarabhaya (1970).
In case of thin cell layer of this species, NAA (1 mg/l) in combination
with BA (3 mg/l) were required for a large number of