FERTILIZATION AND DEVELOPMENT OF SEED 1 8$ 



304. Development of the embryo. The fertilized egg now 

 grows and divides into two cells, and these into more cells, forming 

 the young embryo which lies in the sac within the ovule. This 

 is why the term embryo sac is employed for this structure. At the 

 time of fertilization the endosperm begins to form, and develops 

 the tissue, some of which is used in the growth of the embryo, and 

 the rest is stored as food, either by the side of or around the embryo, 

 or in the cotyledons, according to the kind of seed, for use by the 

 young seedling. 



305. Formation of the seed. We are now ready to learn 

 how the seed is formed. In the bean, pea, squash, and many 

 other seeds, the embryo uses up all of the endosperm which is 

 formed, storing up in the cotyledons what is not used in making 

 the tissues of the different parts of the embryo. During this 

 process nearly or quite all of the inside portion of the ovule has 

 been used as food for the developing endosperm. There remain 



Fig. 145- 



Seed' of violet, external view, and 

 section. The section shows the embryo 

 lying in the endosperm. 



Fig. 146. 



Section of fruit of pepper (Piper 

 nigrum), showing small embryo lying 

 in a small quantity of whitish endo- 

 sperm at one end, the perisperm 

 occupying the larger part of the in- 

 terior, surrounded by pericarp. 



then the walls of the ovule (the integuments), which make the 

 walls of the seed. Inside lies the embryo, with sometimes a papery 

 remnant of the interior of the ovule, as in the squash, pumpkin, 

 etc. In the forming grain of corn, wheat, castor bean, etc., the 

 embryo uses up only a portion of the endosperm, so that in the 

 seed there are embryo and endosperm, surrounded by the walls of 

 the ovule; the embryo and endosperm with the enveloping ovule 



