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THE CONTINUITY OF THE RACE 



The structure of a typical flower. The parts that make up the flower 

 may be divided into essential and accessory structures. 



The essential parts are the sporophylls, which produce the small and 

 large spores from which develop the male and female gametophyte plants 

 and thus ultimately the male and female gametes. The microsporophylls, 

 in which the microspores develop, are the stamens, each consisting of a 

 filament or stalk supporting an anther or spore-producing (and eventually 

 pollen-bearing) organ. Each stamen is a single microsporophyll. The 

 megasporophylls, which produce the megaspores (from which the female 



Fig. 17.10. Imperfect flowers of the squash (gourd family, Cucurbitaceae). Left, the 

 staminate "male" flower; right, the pistillate "female" flower. Both these flowers are 

 incomplete as well as imperfect. (Photos by Prof. E. B. Mains.) 



gametophyte develops), form the pistils. Each pistil consists of a basal 

 part, the ovary, in which the female gametophytes develop from megaspores 

 within structures called ovules; a style projecting from the ovary, through 

 which the pollen tube grows to effect fertilization; and a stigma or ex- 

 panded tip of the style, to which pollen adheres. A pistil may consist of 

 a single megasporophyll {carpel), in which case the ovary has a single 

 chamber. More often the pistil is compound, consisting of several fused 

 carpels and having an ovary with an equivalent number of ovule-bearing 

 areas (placentae) in separate chambers or in a large chamber produced 

 by fusion of those of the individual carpels. 



The accessory parts of the flower include: (1) the petals (collectively 

 called the corolla), often large and brightly colored, forming one or more 



