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 
Fic. 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 fertulized. 
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 46. Notice that instead of a single primary endosperm 
nucleus, there are two nucleilyingin contact. These nuclei fuse 
and form the primary endosperm nucleus. A section through 
an ovule of Oats is shown n Figure 47. Point out the embryo 
