When the pollen tube enters the ovule through the funiculus or the integuments,it is called:

Pollen-pistil interaction is:

The entry of the pollen tube into the ovule through the micropyle is known as:

The micropyle is helpful in $......$.

In wheat and rice,pollen grains lose viability within $30$ minutes of their release. In members of the families Rosaceae,Leguminosae,and Solanaceae,the viability is maintained for $...$.

After penetrating the stigmatic and stylar tissues,the pollen tube usually grows down towards the egg because: