276 



REPRODUCTION OF HIGHER PLANTS 



mature, the ripe anther of the stamen splits and scatters the 

 pollen. Agencies, such as wind, insects, or water, may assist in 



Complicated nuclear divisions in the embryo sac of the ovule of a plant result in the formation 

 of eight nuclei, of which one is an egg nucleus and two are polar nuclei. The two polar nuclei lie 

 near the center of the cell. The egg nucleus is the female gamete. 



scattering the pollen. When pollen reaches the stigma of the 

 pistil, it may be caught and held by hairy outgrowths particularly 

 adapted for that purpose. The stigma then secretes certain 

 nutrient materials which the pollen absorbs. After this pollina- 

 tion, the pollen grain germinates by sending out a slender thread- 

 like tube. The pollen tube 

 grows down through the pistil 

 and penetrates the ovule 

 through an opening called the 

 inicropyle. As it grows, cer- 

 tain nuclear divisions take 

 place, which produce two sperm 

 nuclei. The sperm nuclei with 

 their reduced number of chro- 

 mosomes are the male gametes 

 of the plant. 

 Production of the female 



A photomicrograph of a part of an ovule show- -n i i • i 



ing the nuclei in the embryo sac. Compare it gamete. hach OVUlc HI the 

 with the diagram at the top of the page. • p i • ^ i i 



ovarv IS lormed as the out- 

 growth of a few cells from the ovary wall. One of the cells in 

 the interior of the young ovule appears larger and richer in 



