The structure grown by a pollen grain that contains two sperm nuclei is called a pollen tube.

Here's why:

* Pollen grain: The male gametophyte in flowering plants.

* Pollen tube: A tube-like structure that grows from the pollen grain after pollination. It acts as a conduit, delivering the two sperm nuclei to the ovule.

* Sperm nuclei: The male gametes within the pollen tube. One sperm nucleus fertilizes the egg cell to form the zygote, while the other fuses with the polar nuclei to form the endosperm.

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