486 



Introduction to the Study of Science 



the ovary the tip of the tube grows flat against the side of 

 the ovule (Fig. 151). One of the bodies, the generative cell, 

 enters the ovule and comes into contact with the ovum or egg- 

 cell. These gradually unite, becoming a single body within a 



\J 



FIG. 151. How the ovule is fertilized by the generative cell from the pollen 

 tube (diagrammatic). 



single cell-wall in the ovule. This single body, or the fertilized 

 egg-cell, comprises the two principal original bodies derived from 

 the parent plants, and becomes what is known as the embryo. 

 Tfre other body in the tube unites with another part of the cell 

 substances in the ovule, and this combined body develops to 

 form food which is consumed by the growing embryonic plant. 

 232. The seed. The growth of the fertilized ovule is by 

 division and subdivision (Fig. 152), until there is completed 



FIG. 152. Diagram of development of fertilized egg cell. A, fertilized^ 

 ovule ; e, the ovum in A becomes the embryo in B ; C, the developed seed with 

 cotyledons (cot.) and radicle (rad.). 



the development of the embryo or miniature plant, the food 

 supply, and the seed covering, all of which form what we know 

 as the seed. 



