166 LEAVES 



is an advantage. Why are parks desirable in crowded cities ? 

 Why is the air in the country purer than city air ? Is it a good 

 thing to cultivate plants in the house ? Did this experiment 

 require light? If so, is there any reason why we should not 

 have large numbers of house plants in a sleeping room? 



Suggestion. Repeat this experiment, using gas formed 

 by burning a taper under the glass instead of using air from 

 the lungs. 



With advanced students this experiment may be varied 

 by filling the glass with different gases. Will a plant re- 

 move hydrogen? Oxygen? Pure carbon dioxide generated 

 by action of acids on marble ? 



149. LEAVES 



Object To show that leaves make starch. 

 Apparatus. Green leaves, alcohol, lamp, and iodine solution. 



Method. Place any green plant in the strong sunlight 

 for a day. Then snip off a leaf and plunge it into boiling 

 water for one minute. Remove it from the hot water and 

 immerse it in alcohol. What is the effect of the heating and 

 alcohol upon the appearance of the leaf ? 



Now add a drop of iodine solution to the bleached leaf 

 and after a minute remove it and rinse it in water. 



Examine the leaf to detect blue color due to the presence 

 of starch. 



Or, scald in water leaves treated in Experiment 134 and 

 treat them as above with alcohol and iodine solution. The 

 exposed spot will take on the characteristic blue of the starch 

 test, while the remainder of the leaf will show no trace of 

 starch. 



Conclusion. State the result of these experiments as to 



