The Floral Nectary of Tropaeolum majus L.—The Nature of the Secretory Cells and the Manner of Nectar Secretion

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Abstract
The floral nectary of Tropaeolun majus L. was studied with the aid of a microscope with transmitting and incident light, a transmission electron microscope and a scanning electron microscope. The Gomori method was used for the localization of acid phosphatase. As a result of this investigation the previously accepted view that nectar in this plant is secreted only from the hair tips of the inner epidermis of the calyx spur was found to be inaccurate. The present studies showed that the parenchyma cells located between the inner epidermis and the region of the vascular bundles of the lowest third of the spur, are the main nectar-secreting elements of the nectary. These secretory cells release the nectar solution into intercellular spaces leading to modified stomata, through which it is exuded into the spur cavity. The modified stomata occur in the lowest portion of the spur only. At the stage of secretion small droplets of liquid of high viscosity were observed on the epidermal hairs. These droplets presumably contain polysaccharides and a certain amount of sugar.

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