LIFE HISTORY OF AN ANGIOSPERM 57 



the synergids and fuses with the nucleus of the egg to form an 

 oospore. By this time the tube nucleus has disintegrated. The 

 oospore by repeated divisions develops into as many as four embryos 

 or young sporophyte plants. Only one of these, however persists. 

 The polar nuclei fuse to form the endosperm nucleus which soon 

 undergoes rapid division into a large number of nuclei scattered 

 about through the protoplasm of the embryo sac. Later cell walls 

 are laid down and endosperm is formed. The endosperm cells soon 

 become filled with abundant starch which is later to be utilized by 

 the embryo during germination. 



RIPENING OF THE OVULE TO FORM THE SEED AND OF THE OVARY 

 TO FORM THE FRUIT 



When the embryo and endosperm are being formed, the ovule 

 enlarges and its integuments become modified to form a hard horny 

 seed coat which encloses the endosperm surrounding the embryo. 

 The ovary, containing the ovules, has by this time ripened to form 

 a three-valved loculicidal capsule enclosing the seeds. 



GERMINATION OF THE SEED AND DEVELOPMENT OF THE 

 MATURE SPOROPHYTE 



The seeds are fully developed by June or July when the capsule 

 or fruit splits open to discharge them. They fall to the ground and 

 lie dormant until the following spring when they germinate or com- 

 mence to grow. Each seed absorbs water from the ground which 

 stimulates the ferment amylase, contained in the endosperm cells, to 

 break up the insoluble starch into soluble sugar which passes into 

 solution and diffuses into the cells of the embryo, where the proto- 

 plasm changes it into additional protoplasm and so the embryo 

 increases in size, therefore, grows. The pressure of the swollen 

 endosperm and growing embryo becomes so great that the seed coat 

 bursts; the hypocotyl emerges first, dragging the cylindrical cotyle- 

 don out of the seed coat and epicotyl with it. The hypocotyl elon- 

 gates and extends itself into the soil where it develops a root near 

 its tip. The tip enlarges through the storage of starch, manufac- 

 tured by the green cotyledon and becomes a bulb. The bulb soon 



