Question

Describe devices in plant that prevent both autogamy and geitonogamy

Answer 1

Production of unisexual flowers so that male and female parts will be present on different plants (dioecious) or on different flowers in same plant (monoecious). It prevents both autogamy and geitonogamy.
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Answer 2

In some classes, micro-spores discharge and stigma willingness are not synchronized. Either the micro-spores are discharged before the stigma grows responsive or stigma becomes perceptive before the deliverance of micro-spores. It blocks autogamy.

2. Anther and the stigma of a shoot are arranged in such a way that micro-spores of the corresponding bulb do not come in contact with the same flower.