The quality of Brassica and Acacia pollen is adversely affected by exposure to secretions drawn from the metapleural gland of the ant Myrmecia nigriscapa. Ultrastructural studies show that the apparently lipoidal secretions destroy both the plasma membranes and those of the cytoplasmic organelles. Exposure to the integument of this ant prevents the normal hydration of pollen grains. Exposure to the integument of a species of Camponotus, which does not appear to possess metapleural gland openings, also reduces pollen quality. Mycelial development in seven species of soil‐dwelling fungi is inhibited by secretions of the metapleural gland. Two fungal species that are normally entomogenous are most vulnerable to the secretion. It is suggested that the metapleural gland is producing a powerful antibiotic and that the antibiosis that results from its activity, on one hand, alleviates the attacks of microorganisms in nest cavities, while on the other, incidentally kills pollen grains, possibly blocking the evolution of ant pollination systems.

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The cellular sites of the glycoproteins Group 1 allergen (glycoprotein 1) and Antigen A (glycoprotein 2) in mature ryegrass pollen have been investigated by immunoelectron microscopy. Radioimmunoassays confirm previous findings of cross-reactivity between the purified glycoprotein antigens at the high immunoglobulin G (IgG) concentrations used for localization. Freeze-drying of anthers followed by anhydrous processing has been employed because of the water solubility and mobility of the glycoproteins. A double-embedding technique has been developed. This involves, first, embedding anthers in the water-soluble plastic resin JB-4, sectioning and incubating in ferritin-labelled antisera by the indirect method. The sections are then embedded in Spurr's resin for ultra-thin sectioning. Both glycoproteins are found in the following sites: (1) exine and intine wall layers; (2) pollen cytoplasm; (3) the orbicules and anther loculus; and (4) the anther cuticle. In the exine arcades and surface and in the anther loculus, the ferritin label is bound to pollenkitt. The finding that the glycoproteins are in similar sites is predictable in view of the cross-specificity of the antisera. The extent of antibody penetration of the plastic sections has been examined; labelling is confined to cut grains and absent from intact grains.

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The stigma of Acacia retinodes is receptive from the moment the flower opens (female phase). Receptivity, assessed in terms of pod set, is highest at flower opening, and lowest the following day (male phase). Stigma receptivity is associated with the acquisition of a heterogeneous stigma exudate, the components of which are secreted sequentially during differentiation. Cytochemical probes have tentatively identified the principal components as unsaturated and saturated lipids, free fatty acids, flavonoid aglycones, carbohydrates, proteins and phenolic compounds. The onset of male phase in unpollinated stigmas is associated with a breakdown of the plasma membrane and organelle membranes of stigma cells, and subsequently a browning reaction.