FLOWER: MEMBERS AND ORGANS. 335 



Comparison of Organ and Member. 



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 angio- 

 sperms. 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, 



