Chapter 20 PA - Chapter 20: Flower Structure and...

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1.) Overview Introduction Floral organs and their arrangement Sepals and petals Stamen Gynoecium—the carpel, ovary, style and stigma Vascular system Development: histogenesis, organogenesis, genetic control 2.) What is a flower? The classical theory of the nature of the flower is that a flower is a condensed, determinate shoot system and all of the individual floral organs are more or less modified leaves. Much evidence exists to support this theory including some recent genetic studies. The individual organs are arranged on the more or less contracted shoot homolog called the receptacle. Primitive flowers have elongated receptacles and free organs attached in a long spiral . More advanced flowers have shortened receptacles with organs attached in whorls and the organs may be fused. 3.) Atchaefructus lianingensis From the cretaceous in China. The leaf-like structures on the stem of this 140 million year old fossil are pods containing the seeds, a characteristic unique to flowering plants. Credit of University of Florida. 4.) Figure: Basic floral morphology: stamens, carpels, petals, pistils (don’t use pistil), receptacle, peduncle, sepal, calyx. If petals and sepals are indistinguishable (Tulips), then you would term them (petal+sepal) tepals, or perianth for plural. 5.)Sepals and Petals Sepals and petals are highly leaf-like, both externally and internally, and sterile. They are often green and have a leaf like shape. Generally they have 3 supplying traces or vascular bundles as many leaves do. Modifications from the basic leaf-like plan include additional pigmentation, missing or poorly developed palisade mesophyll, and various epidermal modifications (especially prominent petals). 6.) Figure: petals (corolla), sepals (calyx), flower stalk, scar where sepal and petals were
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Chapter 20 PA - Chapter 20: Flower Structure and...

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