The Vegetative Plant Organic

The desired growth response. A large amount of hormone can bring about an inhibition of growth rather than promotion. Different organs respond to different concentration ranges; for example, the amount of auxin needed to increase stem growth would inhibit the production of roots. The same principle applies to another group of chemicals important in cell division, the cytokinins, which can be applied to leaf cuttings to increase the incidence of plantlet formation. Both chemicals must be included in a tissue culture medium, at concentrations appropriate to the species and the type of

After the germination of the seed, the plumule establishes a direction of growth due partly to the geotropic and phototropic forces acting on it. Often the terminal bud of the main stem sustains the major growth pattern, while the axillary buds are inhibited in growth to a degree which depends on the species. In tomatoes and chrysanthemums, the lateral shoots will grow out, but are inhibited by a high concentration of auxin which accumulates in these buds. The source of the chemical is the terminal bud which sustains a promotive concentration. Removal of the main shoot, or stopping, takes away the supply to the axillary buds which are then able to grow out to a degree, dependent on the exact concentration retained..

The emergence of the plumule above the growing medium is usually the first occasion that the seedling is subjected to light. This stimulus inhibits the extension growth of the stem so that it becomes thicker and stronger, but the seedling is still very susceptible to attack from pests and damping-off diseases. The leaves unfold and become green in response to light, which enables the seedling to photosynthesize and so support itself. The first leaves to develop, the cotyledons, derive from the seed and may emerge from the testa while still in the soil, as in peach and broad bean (hypogeal germination), or be carried with the testa into the air, where the cotyledons then expand (epigeal germination), e.g. in tomatoes and cherry.The emergence of the plumule above the growing medium is usually the first occasion that the seedling is subjected to light. This stimulus inhibits the extension growth of the stem so that it becomes thicker and stronger, but the seedling is still very susceptible to attack from pests and damping-off diseases. The leaves unfold and become green in response to light, which enables the seedling to photosynthesize and so support itself. The first leaves to develop, the cotyledons, derive from the seed and may emerge from the testa while still in the soil, as in peach and broad bean (hypogeal germination), or be carried with the testa into the air, where the cotyledons then expand (epigeal germination), e.g. in tomatoes and cherry.