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). Within this large 

 cell, called the e^nbryo sac, the protoplasm divides and grows, 

 becoming a 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. A 

 nucleus of the em- 

 bryo sac must first 

 unite with the 

 nuclear substance 

 of a pollen grain. 

 The uniting of two 

 nuclei is called 

 fe rtiliza tion . The 

 method by which 

 the two nuclei are 

 brought together is 

 shown in Fig. 134. 



355. Seed and fruit. After fertilization the combined nu- 

 cleus, containing protoplasm from two parents, divides into 

 very many cells. The mass 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, sur- 

 rounding 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 em- 

 bryo 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 



