WILD YELLOW LILY 117 



sac. During the growth of the pollen tube the antheridial 

 cell divides into two sperm cells. 



Fertilization. When the pollen tube has grown down 

 through the style and the tissues of the nucellus and past 

 the synergids the pollen tube breaks and the sperm cells are 

 discharged into the embryo sac. One of the sperm cells 

 fuses with the egg cell to form the young embryo. The other 

 sperm cell fuses with the endosperm nucleus and forms the 

 endosperm. The integuments form the testa, the nucellus 

 the inner seed coat, and the endosperm nucleus the endosperm. 

 The fertilized egg cell becomes the young embryo and con- 

 sists of a radicle, caulicle and one cotyledon. 



SUMMARY OF MONOCOTYLEDONS 



Gametophyte. The male and female gametophytes are 

 still further reduced in the monocotyledons. 



Male Gametophyte. The microsporophylls or stamens 

 constitute the third circle of the flower. The anthers bear 

 the pollen grains. The pollen grains develop into male 

 gametophytes consisting of but two cells, the generative 

 and the tube cell. The tube cell develops the pollen tube 

 which grows through the tissues of the style and conducts 

 the sperm cells to the ovary. 



Female Gametophyte. The megasporophylls or pistils 

 form the fourth and innermost circle of the flower. The 

 ovary or enlarged hollow part of the pistil encloses the ovules; 

 enclosed ovules are characteristic of the monocotyledenous 

 and dicotyledenous plants. The megaspore of each ovule 

 develops the female gametophyte or embryo-sac containing 

 a female cell or egg and six other cells, seven in all. Double 

 fertilization occurs, one sperm unites with the egg cell to 

 form the embryo-sporophyte characterized by having one 



