NATURE OF PLANTS 



117 



54. The Germination of the Gametospore and the Formation 

 of Seed.^The first indication of the germination and growth of 

 the gametospore is seen directly after fertilization. It becomes 



Fig. 81.. Germination of the gametospore of peppergrass, Lepidium: A, 

 micropylar end of the embryo sac showing that the gametospore, g (fertilized 

 female gamete), has developed a cell wall and become attached to the wall 

 of the embryo sac. Compare Fig. 80. B, later stage in the germination — e, 

 embryo cell; s, suspensory cells; en, endosperm cells. C, the embryo cell 

 has formed two cells. D, later stage. The embryo cell by further division 

 has formed a spherical mass of cells, here shown in section. Note the appear- 

 ance of an outer layer of cells, the epidermis, and a central or stem region: 

 s, a few of the suspensory cells. E, still later growth. Two growing regions, 

 the cotyledons are appearing on the side of the stem. F, the micropylar end of 

 the embryo sac, showing the stage of development where the parts of a small 

 plant can be clearly recognized — c, cotyledons; st, stem ending in root, r 

 to which is still attached the suspensory cells; en, endosperm cells, now pro- 

 vided with walls, are being absorbed as the plant or embryo enlarges. Note 

 that the embryo and embryo sac are slightly bent to the left. This curvature 

 is due to the fact that the ovule in a great many plants becomes curved in 

 its development with the result that the embryo sac assumes a curved or 

 U-shaped form. This form of the ovule results in a complete bending over 

 of the cotyledons against the stem, as shown in the next figure. 



