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Leaves of Chrysanthemum cinerariaefolium at various stages of development were found to contain differing amounts of pyrethrins. The variation corresponds to the number of oil glands per unit area of leaf surface. Leaf tissue was mechanically and enzymatically separated into lower and upper epidermis and mesophyll cells. Pyrethrins were found to be present in each layer, more pyrethrins were present in the epidermal layers of young leaves while the mesophyll cells were found to have higher pyrethrins in older, more mature cells.
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Zito et al. (1983) studied this question.
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