Answer:
The correct option is the 4. Pollen tube.
Explanation:
When the male gametophyte of seed plants germinates a tubular structure produced which is pollen tube. Pollen tube extension is an important stage in the plant cycle.
They act as duct or tube to move the male gametes from the pollen grain from the stigma in angiosperms to ovules at the end of the pistil or straight through ovule in some of the gymnosperms.
Thus, the correct option is 4. pollen tube
