REPRODUCTION IN PLANTS AND ANIMALS 371 



of a young ovule and examine it under the microscope, we 

 see that in its center there is an elongated sac, the embryo sac. 



At one end of the em- 

 bryo sac the egg cell is 

 formed. Eggs may there- 

 fore be found in the flow- 

 ering plant just as truly as 

 in animals, but these eggs 

 remain inclosed within the 

 ovary and are not set free 

 as in the frog. 



381. The stamen. The 

 swollen tip of the stamen 

 is the anther. Within the 

 anther there are many 

 small cells, the pollen 

 grains, which, when the 

 anther breaks open, are scattered in small clouds like yellow 

 dust. When the pollen grams alight on the stigmatic end of 



stamen 



FIG. 172. 



^. pistil 



Diagram of flower, showing 

 the different parts 



FIG. 173. Diagram to show development of young plant from the egg 



A, entire pistil; B and C, development of seed; I), seedling plant; pol., pollen 



grain; p. t., pollen tube; ov., ovule; sac, embryo sac; emb., embryo; sd., 



mature seed 



the pistil important changes follow. From the inner wall of 

 the pollen grain there develops a tubular outgrowth which 



