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seed, fertilized and ripened ovule, consisting of the plant embryo, varying amounts of stored food material, and a protective outer seed coat. Seeds are frequently confused with the fruit enclosing them in flowering plants as in the grains and nuts. The seed-bearing plants are the highest in the evolutionary scale; in lower plants (e.g., mosses and ferns) the spore is the agent of propagation. True seeds vary in size from the dustlike seeds of some orchids to the large seed contained in the coconut. The period of dormancy undergone by many seeds before germination also varies; the mangrove seed may sprout inside a fruit still hanging on the tree, while the seeds of a sacred lotus found embedded in peat in Manchuria were viable after 2,000 years. Long dormancy in some seeds is ensured by their extremely hard coats, which have to be scratched or split to force sprouting. In plant breeding, the source of pollen for fertilization is carefully controlled to produce the desired qualities in seed; under natural conditions a plant grown from seed may be quite different genetically from its maternal plant (see fertilization).
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