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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.

A nutritive plant tissue distinct from the plant embryo; it may remain in the mature seed or be depleted during development.^[ref]

Seed germination is renewed plant embryo activity and growth. Many germination assays score completion as radicle emergence, before seedling establishment. Seed imbibition precedes that endpoint; swelling alone is insufficient.^[ref]

Water, molecular oxygen and suitable temperature support germination; light sensitivity depends on the species and seed state. Neither illumination nor one particular temperature is universally required. Seed dormancy connects germination timing to ecology by delaying seedling establishment.^[ref]

The distinction matters when comparing propagation experiments: a treatment that increases radicle emergence need not improve later seedling survival. Define the endpoint before comparing treatments, then measure the later outcome separately.

The young plant inside a seed; its cotyledons and radicle are parts of the plant embryo.

A grouping of biological cells in a plant with related functions. In a seed, plant embryo tissues and endosperm have distinct developmental identities.

A seed packages a plant embryo, a seed food reserve and a protective seed coat. It is a living starting point for a new plant, not merely stored food. In a mature pea seed, the large cotyledons hold reserves; other seeds retain substantial endosperm. These are alternative arrangements, not successive germination stages.^[ref]

A useful reading exercise is to identify both the future plant and its initial food supply in each drawing. The large yellow area has the same role in both pictures, but it belongs to different plant tissues. Thus location and function alone do not establish tissue identity.

The protective covering of a seed, formed from maternal plant tissues surrounding the developing plant embryo.

The stigma is the carpel's pollen-receiving region. Compatible pollen may form a pollen tube that grows toward an ovule; arrival alone does not establish fertilization.^[ref]

A useful diagnostic question is what was actually observed: pollen on a stigma, a growing pollen tube, or a new plant embryo? Each observation tests a different stage. A pollen tube germination assay isolates the middle process for direct viewing.