Seed viability was determined by the ability to reduce 2,3,5-triphenyltetrazolium chloride (TTC) to the red coloured formazon(Brewer, 1949). In this experiment, the orchid embryo eitherturned red or stayed colourless after TCC staining, with noambiguous pale red stained seeds being observed. Therefore, seedswith TTC reduction ability (red coloured) were scored as viable. Foreach replicate, 1 ml of the D. bigibbum var. compactum seed suspension, or 0.2 ml of the D. formosum seed suspension (seeabove) were used, so as to result in approximately 1800 seeds ineach assay for each orchid species. The water was then removedand replaced with 1 ml of 0.1% (v/v) TTC aqueous solution. Theseeds were kept in the dark for 24 h before viability determinationby inspection of their colour. Three replicates were performed, andfor each replicate, the seeds were sampled five times, approxi-mately 180 seeds each time, to determine the seed viability, whichis reported as a percentage