
Seeds are covered by the outer skin called seed coat. They are waterproof and meant to protect the embryo inside until the condition is favouirable for germination. Seeds may last for years...
Cabbage growth stages
Stage 1: Cotyledon (seed leaves). No true leaves present.
Stage 2: Seedling, up to 5 true leaves
Stage 3: 6-8 true leaves
Stage 4: 9-12 true leaves. Base of stem is still visible from above.
Stage 5: Precupping (approximately 13 - 19 leaves).By the end of this stage, the base of the stem and the bases of all leaves are concealed when the plant is viewed from above. The innermost heart leaves are growing in an upright fashion and are visible without moving any of the leaves.Stage 6: Cupping (approximately 20 - 26 leaves)
Stage 7: Early Head Formation 2.5 - 4" diameter head
Stage 8: Head Fill 3 - 8" diameter head
Stage 9: Mature 6 -12" diameter head
(http://www.nysaes.cornell.edu/pubs/fls/OCRPDF/101a.pdf) about cabbages going through several stages before harvest. Click for more: CABBAGE GROWTH STAGES