plants-seeds-4

plants-seeds-4 - Fruit wall and one cotyledon removed (a)...

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Seeds and germination - the sunflower The sunflower ‘seed’ is, in fact, a fruit containing a single seed. The ‘seed’ coat consists of the ovary wall and testa fused together. In all respects this acts in the same way as the testa of the other seeds. The sunflower’s germination differs from the broad bean and pea because, once the radicle has emerged, it is the hypocotyl which elongates. This has the effect of either dragging the cotyledons from the fruit wall or carrying the entire fruit above soil fruit wall scar of attachment to flower head plumule radicle cotyledon Sunflower fruit
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Unformatted text preview: Fruit wall and one cotyledon removed (a) fruit wall splits and radicle emerges hypocotyl root hairs hypocotyl cotyledons plumule lateral roots root hairs (b) hypocotyl elongates and draws cotyledons from the fruit wall. Often the fruit wall is carried out of the soil with the cotyledons. It falls off when the cotyledons expand (c) cotyledons are brought above the soil. The arching of the hypocotyl draws the cotyledons backwards through the soil, protecting the plumule from damage . (d) the cotyledons open out, exposing the plumule 4 Sunflower D.G. Mackean...
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