Figure 18.21   Evolution of the angiosperm fl ower: (a) cone of the Jurassic bennettitalean Williamsoniella, showing the female fertile structure, the ovule, contained in a central receptacle, and surrounded by the male fertile structures, the microsporophylls; (b) fl ower of the gnetale Welwitschia, showing the central ovule, and surrounding male elements; and (c) fl ower of the angiosperm Berberis, showing the same pattern, but with the seed enclosed in a carpel.

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