180 BOTANY. 



95, L). This opening is called the "micropyle," and allows the pollen 

 tube to enter. 



The full-grown embryo sac shows the same structure as that already 

 described in Monotropa (page 276), but as the walls of the full-grown 

 ovule are thicker here, its structure is rather difficult to make out. The 

 ripe stigma is covered with little papillae (Fig. 95, F) that hold the 

 pollen spores which may be found here sending out the pollen tube. By 

 carefully opening the ovary and slightly crushing it in a drop of water, 

 the pollen tube may sometimes be seen growing along the stalk of the 

 ovule until it reaches and enters the micropyle. 



To study the embryo a series of young fruits should be selected, and 

 the ovules carefully dissected out and mounted in water, to which a little 

 caustic potash has been added. The ovule will be thus rendered trans- 

 parent, and by pressing gently on the cover glass with a needle so as to 

 flatten the ovule slightly, there is usually no trouble in seeing the embryo 

 lying in the upper part of the embryo sac, and by pressing more firmly 

 it can often be forced out upon the slide. The potash should now be 

 removed as completely as possible with blotting paper, and pure water 

 run under the cover glass. 



The fertilized egg cell first secretes a membrane, and then divides into 

 a row of cells (JV) of which the one nearest the micropyle is often much 

 enlarged. The cell at the other end next enlarges and becomes divided by 

 walls at right angles to each other into eight cells. This globular mass 

 of cells, together with the cell next to it, is the embryo plant, the row of 

 cells to which it is attached taking no further part in the process, and 

 being known as the "suspensor." Later the embryo becomes indented 

 above and forms two lobes ($), which are the beginnings of the cotyle- 

 dons. The first root and the stem arise from the cells next the suspensor. 



