when a compatible pollen grain lands on the stigma, the stigma produces a sugary solution in which the pollen grain germinates, producing a pollen tube.
The pollen tube grows down the style. It secretes enzymes as it goes, digesting its way through the tissues of the style. It amy also gain nutrienta from the digested products.
- The pollen tube nucleus is positioed at the tip of the tube, with two male nuclei close behind.
- the pollen tube grows through the gap between the integuments, called the micropyle and passes into the embryo sac.
the pollen tube nucleus disintergrates presumably having completed its function of controllingthe growth of the pollen tubule.
The tip of the pollen tube bursts open releasing the male gametes into the embryo sac and the two male nuclei enter.
one of the male gametes fuses with the female nuclues to form a zygote
the other male gamete fuses with both polar nuclei to form a triploid endosperm nucleus.
thus a double fertilisation occurs, a process unique to flowering plant