Seed selection: the careful selection of seed from particular plants with the object of keeping or increasing some desirable quality.
Seedling: a young plant just from the seed.
Sepal: one of the leaves in the calyx.
Set: a young plant for propagation.
Silo: a house or pit for packing away green food for winter use so as to exclude air and moisture.
Sire: father.
Smut: a disease of plants, particularly of cereals, which causes the plant or some part of it to become a powdery mass.
Spike: a lengthened flower cluster with stalkless flowers.
Spiracle: an air opening in the body of an insect.
Spore: a small body formed by a fungus to reproduce the fungus. It serves the same use as seeds do for flowering plants.