50 A LABORATORY MANUAL OF BOTANY 
it. Mount some of the pollen, examine, and sketch as seen 
under magnification. 
4, The carpels or pistils, the innermost structures of the 
flower. Each carpel or pistil usually consists of a swollen 
base, the ovary, from which extends upward an elongated 
part, the style, which style is terminated by an expanded 
part, the stigma. The style may be absent, in which case 
the stigma rests directly upon the ovary. Sketch the carpel 
of the flower you have. 
Cut across the ovary and observe within it one or more 
small rounded bodies, the ovules. These are the structures 
that develop into seeds. 
In the process of developing a seed one or more of the 
pollen-grains must be placed upon the stigma of the carpel. 
This process is known as pollination. The stigma usually 
secretes a sticky and often sweet substance, which holds the 
pollen-grains when once they have come in contact with it. 
Meanwhile there have developed within the grain at least 
two cells, each of which consists of a nucleus surrounded by 
a small mass of cytoplasm. From the wall of the grain 
there now develops a tube which pushes its way down 
through the tissues of the stigma and style, and the cells are 
carried along in this tube. This tube finally reaches the 
ovule and penetrates it. While the pollen-tube has been 
growing, the ovule has developed an egg-cell in its interior. 
The end of the pollen-tube opens in the immediate region of 
the egg-cell, the cells within the tube pass out into the ovule, 
and one of them unites with the egg-cell. The cell thus 
formed by the union of the two cells begins to grow, and 
gradually develops into the embryo of a new plant. Usually, 
about the time this new plant has developed far enough to 
have formed a small root, one or more leaves, and the begin- 
ning of a stem, the walls of the ovule become hard and dry, 
the young plant within stops in its growth, and we have as 
the result the structure which we call the seed. It may re- 
