Changes in the Pollen Grain Wall of Linum grandiflorum following Compatible and Incompatible Intraspecific Pollinations

The exine surrounding the colpal furrows in the pollen grains of Linum grandiflorum is rapidly degraded following the two compatible pollinations between ‘pin’ and ‘thrum’ types of flower and also following the incompatible pollination between ‘thrum’ and ‘thrum’. In all these pollinations the pollen germinates normally. Exine is not degraded in the incompatible pollination between ‘pin’ and ‘pin’. In this pollination the pollen does not swell or germinate. The exine degradation is restricted to the colpal regions. Hydration of the pollen grain by buffer solution without contact with the stigma also stimulates the degradation of the exine. The erosion of the exine reveals a fibrous, PAS-positive matrix which follows the original contours of the exine.Vesicles are discharged into the intinc following pollination; these appear to contribute their contents to the intine-like wall which eventually invests the pollen tube.The observations are interpreted by assuming: 1. an enzyme situated within the pollen and localized under the colpi; this enzyme is active after hydration;2. the degradation is a means by which colpal furrows are enlarged to permit the emergence of the pollen tube;3. the degradation process both by buffer and on the stigma is purely the consequence of hydration and is only secondarily related to incompatibility through the ‘pin’ by ‘pin’ pollination not permitting hydration of the pollen.