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- In some plants anthers of the flow or of earlie than the stigma (protandry) finger. sweet peas Salvia. sunflower In either ase. condition in which even

1. Self-sterility. This is a candien from the anthers of if the stigma receives polten fom fails to undergo the same flower, the pollen fails only the pollen further growth. In such cases ame species, can from another plant of the same spectess of setting of effectively complete the process of setting orchids. the seeds; 68 - ray florets of sumflowe ac.
2. Herkogamy (herkos : barrier: mechanical or structural barriers). In some flowers, the pollen of a flower cannot reach the stigma of the same flower. For example, a hood covering the stigma acts as a mechanical barrier in flowers of Pansy. Iris, etc.
3. Heterostyly. In such flowers the stigma and anthers grow at different heights which does not favour self-pollination. eg. primrose, Oxalis (Fig. 5.2).

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