Seed Structure and Composition
In a consideration of seed dormancy and germination we are concerned with the form in which a seed is released from the parent plant, whether as a naked seed or as a fruit, part of a fruit or complete inflorescence. The development of the various seed parts, namely testa, embryo, endosperm and perisperm, has been considered in the previous chapter. At the time of dehiscence, the cells of the testa, and where relevant those layers of the pericarp immediately adjoining the testa, will have normally become thickened, lignified and suberized prior to their drying and dying so as to enclose the seed in a tough protective cover. Not all seeds develop tough covering layers, however. In some seeds the testa consists of mucilage cells whose contents anchor the seed to the soil and retain the water which is necessary for germination. Other surface features, such as winged protuberances, hairs, spikes and prickles, may function variously in seed dispersal and in anchoring the seed to the soil. In those seeds where the inner layers of the pericarp take on the protective function, the testa tends to remain thin and undeveloped.
KeywordsShoot Apex Seed Dormancy Castor Bean Embryonic Axis Helianthus Annuus
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