=667. The stamens and pistils are not the sexual organs.=—Before the sexual organs and sexual processes in plants were properly understood it was customary for botanists to speak of the stamens and pistils of flowering plants as the sexual organs. Some of the early botanists, a century ago, found that in many plants the seed would not form unless first the pollen from the stamens came to be deposited on the stigma of the pistil. A little further study showed that the pollen germinated on the stigma and formed a tube which made its way down through the pistil and into the ovule. This process, including the deposition of the pollen on the stigma, was supposed to be fertilization, the stamen was looked on as the male sexual organ, and the pistil as the female sexual organ. We have found out, however, by further study, and especially by a comparison of the flowering plants and the lower plants, that the stamens and pistils are not the sexual organs of the flower. =668. The stamens and pistils are spore-bearing leaves.=—The stamen is the spore-bearing leaf, and the pollen grains are not unlike spores; in fact they are the small spores of the angiosperms. The pistil is also a spore-bearing leaf, the ovule the sporangium, which contains the large spore called an _embryo sac_. In the ferns we know that the spore germinates and produces the green heart-shaped prothallium. The prothallium bears the sexual organs. Now the fern leaf bears the spores and the spore forms the prothallium. So it is in the flowering plants. The stamen bears the small spores—pollen grains—and the pollen grain forms the prothallium. The prothallium in turn forms the sexual organs. The process is in general the same as it is in the ferns, but with this special difference: the prothallium and the sexual organ of the flowering plants are very much reduced. =669. Difference between organ and member.=—While it is not strictly correct then to say that the stamen is a sexual organ, or male organ, we might regard it as a _male member_ of the flower, and we should distinguish between _organ_ and _member_. It is an _organ_ when we consider _pollen production_, but it is not a sexual organ. When we consider _fertilization_ it is _not a sexual organ, but a male member_ of the flower which bears the small spore. The following table will serve to indicate these relations. Stamen = spore-bearing leaf = male member of flower. Anther locule = sporangium. Pollen grain = small spore = reduced male prothallium and sexual organ. So the pistil is not a sexual organ, but might be regarded as the female member of the flower. Pistil = spore-bearing leaf = female member of flower. Ovule = sporangium. Embryo sac = large spore = female prothallium containing the egg. The egg = a reduced archegonium = the female sexual organ. Progression and Retrogression in Sporophyte and Gametophyte.