302 



ELEMENTARY BIOLOGY 



The inside of the ovule is a soft mass, made up of many 

 compartments, or cells, containing the jellylike living matter, or 

 protoplasm. One of these cells, usually near the center, is much 

 larger than the others (see es, Fig. 134). This large cell, called 

 the embryo sac, grows and divides and in time becomes the 

 young plant, or embryo, inside the seed. The rest of the ovule 

 becomes the coat, or covering, of the embryo. 



354. Fertilization. Before the ovule can become a seed, 

 certain changes must take place in the living matter of the 



embryo sac. The 

 nucleus of the em- 

 bryo sac must first 

 unite with the 

 nuclear substance 

 of a pollen grain. 

 The uniting of two 

 nuclei is called 

 fertilisation. The 

 method by which 

 the two nuclei are 

 brought together is 

 shown in Fig. 1 34. 



355. Seed and fruit. After fertilization the embryo sac, 

 which now contains protoplasm from two parents, divides into 

 very many cells. It absorbs food in large quantities from the 

 parent upon which it is borne, and becomes a baby plant, or 

 embryo (see Fig. 120). The walls of the ovule, surrounding 

 the embryo sac, become the seed covers. The ovule with its 

 embryo sac thus changes into a seed. In addition to the food 

 used in the growth of the embryo, the parent plant supplies 

 other food materials that are accumulated either in a mass 

 surrounding the embryo, or within the tissues of the embryo 

 itself. This surplus food may later be drawn upon by the 

 young plant, after it sprouts and before it is able to maintain 

 itself through the work of its own leaves and roots. 



FIG. 133. Sections of ovaries 



Ovaries are of many sizes and shapes. They contain but a 



single ovule in some species of plants, and in other species 



they bear hundreds. The ovules are definitely placed in 



one or more compartments of the ovary 



