Occurrence of Non-functional Stomata in the Flowers of Tropical Orchids

The morphology and physiology of the stomata of several tropical orchid flowers were studied in relation to the transpiration of these flowers. Stomata were present in all orchid flowers studied. The density of stomata in floral parts was considerably lower than in the leaves. Also, the distribution of stomata in various floral parts varied. Floral stomata were incapable of photosynthesis although they contained starch. Stomatal conductance and transpiration were not affected by changes in CO2 concentration, irradiance, relative humidity and abscisic acid treatment. Water vapour conductance in flowers was low and comparable to that of upper epidermis of the leaves which in all cases was devoid of stomata. The transpiration of orchid flowers in light and in dark was identical. This, together with other evidence indicates that stomata in orchid flowers do not function in the control of water loss.