PRODUCTION OF THE MALE GAMETE 



275 



Problem. What effect has a sugar solution on 

 pollen grains ? 



Make up cane sugar solutions of thirty-five per cent, 

 ten per cent, and three per cent. Take three hanging- 

 drop glass slides and on each one lay a cover glass from 

 the center of which hangs a drop of sugar solution con- 

 taining some pollen. Use a different sugar solution for 

 each slide. Seal the cover slip air tight by means of 

 vaseline. (Petri dishes or Syracuse watch crystals may, 

 also, be used.) Different pollen requires different 

 concentrations of sugar solution in order to grow. A 

 three-per-cent sugar solution is usually needed for tulip, 

 narcissus, and onion ; fifteen per cent for sweet pea and 

 nasturtium. Let the preparations stand for one or two 

 days. Then mount under the microscope. 



I. Describe the shape of the pollen grains when first 

 produced by the anther. 



II. Describe what has happened to the grains! 



A. These outgrowths are called pollen tubes. 



B. Describe the food for the pollen tubes which 

 you have grown. 



III. Carefully crush the tip of a ripe stigma on a 

 glass slide and mount under the microscope. 



A. Do you find any pollen grains here? 

 1. How did they get on the stigma? 



B. Do any pollen grains show pollen tubes? 



1. In which direction are they growing? 



2. Where must the germinating pollen tubes 

 obtain their food ? 



IV. Draw and label a germinating pollen grain. 



sperm.. 



Production of the male gamete. Pollen is 

 produced in the anther of the stamen. Certain 

 cells in the anther go through a maturing 

 process in which reduction division takes place, 

 Mature pollen nuclei contain one half the number of chromosomes 

 characteristic of the other cells of that particular plant. When 



A pollen grain has two 

 nuclei, one a tube nu- 

 cleus, the other a gener- 

 ative nucleus. As the 

 pollen grain forms the 

 pollen tube, male gam- 

 etes (the sperm nuclei) 

 are produced from the 

 generative nucleus. 



