REPRODUCTION 



235 



microscope, we find that in the center of it there is an 

 elongated sac known as the embryo sew. This contains 

 protoplasm and several nuclei. One of these nuclei, 

 together with the protoplasm immediately around it, 

 forms the egg cell. The pollen grains are formed in 

 the anther of the stamen. When the anther breaks 

 open these small cells are scattered and some fall upon 

 the stigma. Changes then take place in the pollen 

 grain and as a result a tube, the pollen tube, develops. 

 This tube continues to grow downward through the 

 stigma and style. It enters the ovule and grows toward 

 the egg. During this time two cells, sperm cells, have 



From Caldwell and Eikenberry's "Elements of General Science," 

 by permission of Ginn and Company, Publishers. 



Fig. 101. Diagram to show development of young plant from 

 the egg. A, entire pistil ; B and C, development of seed ; D, seed- 

 ling plant ; pol., pollen grain ; p. t., pollen tube ; ov., ovule ; sac, 

 embryo sac ; emb., embryo ; sd. } mature seed. 



developed in the pollen tube. One of these sperm 

 cells may unite with the egg cell and form a single 

 cell. This process is known as fertilization. After 

 fertilization this egg begins to divide and to form the 

 new plant. One region develops into the root tip, 



