Summary Applications of ABA to Cymbidium flowers induce some, but not all, post‐pollination symptoms. Anthocyanin levels in sepals, petals, columns and labella are raised; flowers wilt; dorsal sepals become hooded; calli develop colouration while losing turgidity; columns do not swell, lose very little curvature; and stigmas do not close. Combinations of ABA and NAA induce all post‐pollination phenomena, but lower anthocyanin content than treatments with ABA only. ABA plus GA3 have effects which are similar to those of ABA alone, except that anthocyanin levels are reduced. The same is essentially true of ABA‐kinetin mixtures but intensities of the effects are different and with some concentration ratios, stigmatic closure also occurs. The effects of ABA and its interactions with GA3, kinetin or NAA are explained in terms of the roles these hormones may play in synthesis of nucleic acids and enzymes.

SUMMARY Sugars present in the floral and extrafloral exudates from a number of orchid species have been analysed. All contain fructose, glucose and sucrose. Raffinose is the next most common sugar and stachyose occurs less frequently. Cellobiose, gentiobiose, lactose, maltose, melibiose, melezitose and a few large oligosaccharides may also be present. The distribution of these sugars in orchids may have some chemotaxonomic implications. There appears to be no correlation between the sugar content of exudates and orchid pollinators. This would seem to suggest that scent, form and colour are the major attractants to pollinators in orchids. Floral and extrafloral exudates in orchids may also function as attractants for ants which probably feed on them and repel grazers.

SUMMARYNAA, in concentrations exceeding o.oi /Ug/flower, initiates post-pollination phenomena in Cymbidium (Orchidaceae) flowers similar to those brought on by pollination. These include stigmatic closure, swelling and loss of curvature of the column, wilting of the perianth, deformation of the calli, and anthocyanin production. Applications of relatively high concentrations of GA3 induce post-pollination effects which, except for anthocyanin production, are less intense than those brought about by auxin. Kinetin does not induce post-poUination phenomena, but in concentrations of 10 fig and 100 ^g/flower causes slight stigmatic closure, and in some combinations with NAA it inhibits wilting. Stigmatic closure, loss of column curvature and changes in calli, all of them NAA induced, cannot be prevented by simultaneous applications of kinetin, GAj or ABA. Some combinations of NAA and GA3 lowered anthocyanin content relative to separate treatments with either hormone. Flowers treated with GA3 plus kinetin wilted slightly in most cases, but columns did not swell and retained their curvature; calli did not develop colour and anthocyanin content was generally equal to that of flowers given only kinetin. GA3 and ABA when applied together brought on symtoms which were similar to those caused by ABA only but anthocyanin content was lower than in flowers treated with either hormone alone. This is also true for ABA-kinetin mixtures, but intensities of the effects are different and, with certain concentration ratios, stigmatic closure occurs. The phenomena are discussed relative to fruit-set, seed formation, anthoeyanin production, senescence, orchid biology and the possible mode of action of each hormone.

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