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plants-vr-04-corms-1 - corms Contractile roots The...

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Vegetative reproduction 4 Corms - Crocus Plants with bulbs store food in special leaves or leaf bases. Plants with corms store food in the stem, which is very short and swollen. When the foliage has died off, the leaf bases, where they encircle the short stem, form protective scaly coverings. A familiar corm is that of the crocus (below) and the wild arum corm is illustrated on p.1 Since the corm is a stem, it has lateral buds which can grow into new plants. The stem remains below ground all its life, only the leaves and flower stalk coming above ground. Life cycle (Figs 1-4 on p.5). In Spring, the food stored in the corm enables the terminal bud to grow rapidly and produce leaves and flowers above ground. Later in the year, food made by the leaves is sent back, not to the old corm, but to the base of the stem immediately above it. This region swells and forms a new corm on top of the old, now shrivelled, corm. Some of the lateral buds on the old corm have also grown and produced new plants with
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Unformatted text preview: corms. Contractile roots The formation of one corm on top of another tends to bring the successive corms nearer and nearer to the soil surface. Adventitious roots develop from the base of the new corm. Once these have grown firmly into the soil, a region near their junction with the stem contracts and pulls the new corm down, keeping it at a constant level in the soil. Wrinkles can be seen on these contractile roots where shrinkage has taken place. Bulbs also have contractile roots which counteract the tendency in successive generations to grow out of the soil. circular sheath new corm forming contractile root adventitious root old corm lateral bud growing scar left by last year’s circular leaf base leaf remains of flower new corm old corm lateral bud growing Crocus corm in Spring Longitudinal section through crocus corm © D.G. Mackean...
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