By the use of an immunofluorescence technique, the main source of the antigens released by the pollen grains of Phalaris tuberosa L. (Gramineae) on leaching has been shown to be the intine. The main concentration is in the thickened zone underlying the germination pore. The intine is also the site of various hydrolytic enzymes.

The fate of the intine-held antigens has been followed in compatible and incompatible pollinations. They are lost on to the stigma within 5-10 min, whether or not the pollen grains germinate. Where germination does occur after a compatible pollination, the antigens remain spread on the surface of the stigma cells after the tubes have penetrated. There is no indication that antigenic material of the same type is released during the further growth of the tubes.

The possible roles of the intine-held materials as recognition substances in inter- and intra-specific compatibility reactions are discussed.

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