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TEXTBOOK OF BOTANY 



micropyle. A sticky liquid is formed in the micropyle and 

 oozes from its mouth. The jarring of the cone by the wind 

 shakes the pollen grains about, and when they come in con- 

 tact with this liquid they are held by it. Then a drying oc- 

 curs within the micropyle and the drop of liquid is sucked 

 back, carrying the pollen grains to the bottom of the micro- 

 pyle. The pollen grains are now in contact with the macro- 

 spore sac, within which is the female plant. The set of proc- 

 esses which thus bring 

 i the pollen grain close to 

 the female plant is called 

 pollination. It is plain 

 that pollination must 

 take place before fer- 

 tilization can occur. 



152. Fertilization. 

 After the pollen grain 

 has reached the base of 

 the micropyle, its de- 

 velopment into a male 

 plant continues. The 

 vegetative cell of the 

 pollen grain pushes out 

 a long projection the 

 pollen tube (Fig. 74, /). 

 This tube burrows into the tissues of the macrospore sac, grow- 

 ing very slowly, occasionally branching, and using for food 

 some of the cells of the spore sac. While the tube is growing, 

 the generative cell within the pollen grain divides, forming a 

 stalk cell and a body cell. The body cell next divides into two 

 male gametes, which move, following the vegetative, nucleus, 

 toward the .growing end of the pollen tube. The gametes 

 are simple cells consisting of nucleus and some cytoplasm, 

 and with no -vibrating hairs such as are borne by the male 

 gametes (antherozoids) of mosses and ferns. 



FIG. 74. A lengthwise section of an 

 ovule older than that shown in Fig. 73, C, 

 showing germinating pollen grains, pollen 

 tubes, t, and the upper part of the female 

 plant with three archegones; each arche- 

 gone contains a large egg, e; i, integument ; 

 , an egg nucleus. 



