462 



SPERMATOPHYTES (SEED PLANTS) 



stigma where the male gametophytc completes its development. 

 The history of the pollen is shown in the upper diagram of 

 Figure 409. 



The Pistil. — A i)istil consists of one or more megasporophylls 

 (carpels). The megasporophyll is usually organized into an 



Fig. 409. — The formation of the spores and gametophytes m Angiosperms. 

 The upper diagram shows the origin of the pollen grains and male gameto- 

 phjrtes. a, cross section of a young anther, showing the mother cells; b, a 

 mother cell beginning to divide; c, the first division of the mother cell com- 

 pleted; (/, the second division of the mother cell completed, resulting in a tetrad 

 of daughter cells; c, cells of the tetrad separated and fully formed pollen grains; 

 /, pollen grain with male gametophyte developed, showing tube nucleus at t, 

 and sperms at s. 



The lower diagram shows the formation of megaspores and female game- 

 tophyte. g. section through an ovule, showing the megaspore mother cell 

 with chromatin in a thread in preparation for the reduction division; h, a sec- 

 tion through an ovule, showing the four megaspores resulting from the two 

 successive divisions of the megaspore mother cell; i, section through an 

 ovule showing the mature female gametophyte which is formed by the sur- 

 viving megaspore. 



ovary, style, and stigma. In compound pistils, where a number 

 of carpels are present, the ovaries are usually joined, thus form- 

 ing a compound ovary, and often the styles and sometimes the 

 stigmas are also joined. 



The ovary, which is the enclosure for the megasporangia or 

 ovules, is one of the notable features of Angiosperms. With the 

 ovules enclosed the pollen cannot come in contact with the ovules 

 as it does in Gymnosperms, so the stigma, another characteristic 



