THE PLANT AND ITS PARTS. ii 



it. When the pollen-grains have become fixed upon 

 the stigma, they begin to grow by sending out little 

 tubes, called the pollen-tubes (Fig. 3). 



The tubes grow down the style (Fig. 4, c) till they 

 reach an ovule {gm) within the ovary i^d). In the 



Fig. 3.— Pollen grains putting 

 out their pollen-tubes : a, 

 Teasel ; b, Gourd. 



figure the ovary contains only 

 one central ovule, so the 

 pollen-tube passes directly 

 downwards into a little hole 

 at the upper end of it. It 

 carries down a fertilizing 

 body which meets another in 

 what is called the Emhryo-sac (se), a large cell or cham- 

 ber within the ovule. This ovule has two coats as 

 shown in the figure, called the Primine, the outer, and 

 Secundine, the inner. These surround the solid central 

 body in which lies the embryo-sac (se). 



Fig. 4.— Longitudinal section through 

 the ovary of Polyg'onum Convol'vu- 

 lus at the time of flowering: a, 

 stigma; b, pollen grains ; c, pollen- 

 tube ; d, wall of the ovary ; gm, the 

 erect ovule ; se, its embryo-sac ; ch, 

 chalaza: two pollen-tubes have 

 penetrated through the style, one of 

 which has entered the ovule, the 

 other, not. 



