40 



PISTILS AND STAMENS 



tioned. In some ovules the embryo sac may be seen without 

 the microscope, but in most ovules it is microscopic. There is 

 only one cell and one nucleus in the embryo sac, which have an 

 important function in the formation of the seed. The important 

 cell is the egg. The egg is at the micropylar end and after 

 fertilization produces the embryo of the seed. The important 

 nucleus, referred to as nucleus because it has no definite 

 amount of protoplasm, is the primary endosperm nucleus. It 

 is near the center of the embryo sac and is important because 

 upon it the development of the stored food or endosperm of 

 the seed depends. The remaining cells and nuclei of the 



Fig. 47. — A vertical section through an Oat ovary to show the parts of 

 the ovule. Parts of the lemma, palea, and two stamens are shown, and one 

 style and stigma remains. Label the parts of the ovule. Much enlarged. 



embryo sac are absorbed and disappear soon after the egg is 

 fertilized. In the ovules of Clover and many other plants, the 

 cells at the inner end (chalazal end) of the embryo sac disappear 

 even before the egg is fertilized. 



A section through an ovule of Red Clover is shown in Figure 

 45. Point out the embryo sac. Notice the egg at e and the 

 endosperm nucleus at en. Point out the embryo sac of Corn in 

 Figure 1^6. Notice that instead of a single primary endosperm 

 nucleus, there are two nuclei lying in contact. These nuclei fuse 

 and form the primary endosperm nucleus. A section through 

 an ovule of Oats is shown n Figure 1^1. Point out the embryo 



