How does cleistogamy ensure autogamy?

Explanation

(a)Cleistogamous flowers do not open at all, In such flower , the anthers and stigma lie close to each other. When anthers dehisce in the flower buds, pollen grains come in contact with stigma to effect pollination. So cleistogamous flowers are autogamous as there is no chance of cross pollen landing on stigma.
(b)Advantage:Cleistogamous flowers produc assured seed-set even in the absence of pollinators
Disadvantage :Genetic variations will not be exhibited by cleistogamous flower and hence the plants will suffer from inbreeding depression.