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In the common angiosperm arrangement, one sperm fuses with the ovum to form a diploid zygote; another fuses with the central biological cell's two polar cell nuclei, initiating endosperm with three chromosome sets. The zygote develops into a plant embryo, and the ovule develops into a seed.^[ref]

For an original counting example, stipulate a plant with $2n=14$ chromosomes and the common two-polar-nucleus arrangement. Each haploid sperm and ovum contributes $n=7$. The zygote therefore has $7+7=14$ chromosomes, while the initiating endosperm cell nucleus has $7+7+7=21$. The maternal seed coat remains derived from $2n=14$ plant tissue; the whole seed has no single uniform chromosome count. This is bookkeeping for a stipulated example, not identification of a particular species. It follows by counting the chromosome sets entering each fusion, rather than assigning one count to everything enclosed by a seed coat.

An angiosperm pollen grain is a small male gametophyte, not itself a seed or a single gamete. Its tube-forming biological cell supports delivery of sperm.^[ref]

A growing extension from a pollen grain. In a compatible flower, the pollen tube provides a route for sperm to the angiosperm female gametophyte.^[ref]