In sausage tree (Kigelia africana) the pollination takes place by

Apogamy is

In angiosperms, functional megaspore develops into

When the pollen grains are not transferred from anthers to the stigma in flower due to the barrier or fence, it is referred as or when some natural barrier exists between androecium and gynoecium to check self pollination, it is known as

The role of double fertilization in angiosperms is to produce