REPKODUCTION BY SEED 



163 



is formed inside a large cell the embryo-sac, which 

 is developed in the tissues of the ovule. The egg 

 always remains where it is formed, and therefore the 

 male cell must be brought to it. In the higher seed- 

 plants the Angiosperms (Gr. angios, a vessel ; sperma, 

 seed) the ovules are enclosed in the ovary, and the 

 pollen-grains can be brought no nearer to the ovules 

 than the stigma. In the lower group of seed-plants 

 the Gymnosperms 

 (Gr. gymnos, naked), 

 pines, firs, cypresses, 

 larches, yews the 

 ovules are not en- 

 closed, but lie ex- 

 posed to the air. In 

 this case the pollen 

 can be borne direct 

 to the entrance of 

 the ovule. The first 

 step in the produc- 

 tion of seed is the 

 conveyance of the 

 pollen to the stigma 

 of the pistil, or in 

 the case of Gymno- 

 sperms to the ovule 

 itself. This is termed 

 pollination. When 

 the pollen - grain is 

 deposited upon the 

 stigma it germinates. 



A -i vi k, micropyle of ovule ; I, egg-cell ; m, em- 



long thread - like bryo-sac ; n> integument of ovule ; r, re- 



ceptacle. 



FIG. 66. DIAGRAM OF FLOWER AT TIME 

 or FERTILIZATION. (AFTER PRANTL AND 

 VINES.) 



a, calyx ; 6, corolla ; c, stamens ; d, anther ; 

 e, pollen-grains ; /, tube of germinating 

 pollen-grain ; g, stigma ; h, style ; i, ovary ; 

 k, 



tube grows out of 

 the grain, penetrates 



the style, and makes its way towards the ovule. The 

 body of the ovule within which the egg is formed is sur- 

 rounded by one or two coats, but a hole, or pore, is left in 

 the coats the micropyle (Gr. mikros, small ; pyle, gate) 

 which 'affords a passage to the interior. On entering the 

 ovary, the growth of the pollen-tube is directed towards 

 the lips of the micropyle. A liquid secreted at the 

 micropyle attracts in some way the elongating tube. 

 The tip of the tube enters the ovule, and, reaching 



