REPRODUCTION IN PLANTS 



75 



1. Describe what you have done. 



2. Examine the surface of the stigma with a magnifier and 



state what causes the pollen to stick to the stigma. 



88. Microscopical Demonstration of Pollen Grains and their 

 Development. Laboratory Study No. 44. (Optional.) Prepare 

 some sugar solution by adding to ten teaspoonfuls of water one 

 teaspoonful of molasses or grape sugar and heat to boiling point. 

 Put some of this sugar solution in a clean Syracuse watch 

 glass. When the solution has cooled, mix with it some pollen 

 from the flower of a tulip, a trillium, a sweet pea, or nasturtium. 

 Several of these glasses might well be prepared with slightly dif- 

 ferent strengths of sugar solution and piled one above the other to 

 keep out mold spores. Leave the glasses until the pollen grains 

 have germinated. Study the preparation with the low power of 

 the compound microscope. 



1. Find some pollen grains that have not begun to grow tubes. 

 Describe the form of one of the pollen grains. 



FIG. 26. Different kinds of pollen grains, highly magnified, two of them 

 forming pollen tubes. (Duggar.) 



