FERTILIZATION 



215 



the ovule m, in Fig. 165, reaches one of the cells shown 

 at e, and transfers a generative cell into this egg-cell. The 

 latter is thus enabled to 

 divide and grow rapidly 

 into an embryo. This 

 the cell does by forming 

 cell-walls and then in- 

 creasing by continued 

 subdivision, in much the 

 same way in which the 

 cells at the growing point 

 near the tip of the root, 

 or those of the cambium 

 layer, subdivide. 1 



227. Nature of the 

 Fertilizing Process. 

 The necessary feature of 

 the process of fertiliza- 

 tion is the union of the 

 essential contents of two 

 cells to form a new one, 

 from which the future 

 plant is to spring. This 

 kind of union is found 

 to occur in many cryp- 

 t o g a m s (Chapters 

 XX-XXII), resulting 

 in the production of 

 a spore capable of grow- 

 ing into a complete plant like that which produced it. 



1 See Kerner and Oliver's Natural History of Plants, Vol. II, pp. 401-420. 



FIG. 165. Diagrammatic Representation of 

 Fertilization of an Ovule. 



i, inner coating of ovule ; o, outer coating of 

 ovule; p, pollen tube, proceeding from one 

 of the pollen grains on the stigma ; c, the 

 place where the two coats of the ovule 

 blend. (The kind of ovule here shown is 

 inverted, its opening m being at the bottom, 

 and the stalk / adhering along one side of 

 the ovule.) a to e, embryo sac, full of pro- 

 toplasm ; a, so-called antipodal cells of em- 

 bryo sac ; n, central nucleus of the embryo 

 sac ; e, nucleated cells, one of which, the 

 egg-cell, receives the essential contents of 

 the pollen tube ; /, f uniculus or stalk of 

 ovule ; m, opening into the ovule. 



