ANGIOSPERMS 409 



expand into green leaves showing also some intermediate stages 

 with partly developed anther sacs or ovules on them. 



556. The stamen is a microsporophyll. The function of 

 the stamen is the production of pollen. Each pollen grain is 

 a spore, and four are formed from a mother cell in the anther 

 sac just as the spores of the ferns, mosses and liverworts are 

 formed. When the pollen grain germinates it produces the pollen 

 tube and two sperm cells. It is therefore the male gametophyte. 

 The pollen spore is the microspore, the anther sac is the micro- 

 sporangium, and the stamen is the microsporophyll. 



557. The pistil, or carpel, is a macrosporophyll (=mega- 

 sporophyll). The simple pistil is a carpel, while a compound 

 pistil is formed of several carpels united. The pistil is com- 

 posed of the ovary, the style (which may be wanting) and the 

 stigma. The function of the ovary is the production of ovules 

 with the contained embryo sac and egg. The egg it will be 

 remembered in the Gymnosperms is developed by the game- 

 tophyte. The embryo sac with the egg is the female gametophyte 

 of the Angiosperms. It represents the macrospore, just as the 

 female prothallium in Selaginella enclosed by the spore wall is 

 the macrospore (or megaspore). 



The ovule then which produces the macrospore is the macro- 

 sporangium, and the carpel is the macrosporophyll. 



558. The sexual organs of Angiosperms. The stamens and 

 pistils are often spoken of as the sexual organs of the flower. 

 This is not strictly correct, for the sexual organs are borne on the 

 gametophyte and are a part of it, while the stamen and pistil 

 are parts of the sporophyte. While it is not strictly correct then 

 to say that the stamen is a sexual organ, or male organ, it is a 

 male member of the flower for it is a flower member. We should 

 then distinguish between its functions as organ and member. It 

 is an organ when we consider pollen production, but it is not a 

 sexual organ, for the pollen sac is not a sperm case (antheridium), 

 it is a spore case. The spore case is a part of the sporophyll 

 (stamen). But when we consider fertilization, the sperms are 

 formed in the sperm case (antheridium) which is here much 



