COMPOSITION OF LIFELESS AND LIVING THINGS 23 



Secure a plant having some portions that are colorless (e.g. 

 striped grass). Expose the plant to sunlight for two or three 

 hours, then remove several leaves and test them in the same 

 manner as described in 29 above. 



1. State briefly how the preparation of this experiment 



differs from that of the two preceding experiments. 



2. What is your observation and conclusion as to the pres- 



ence of the starch in the green and colorless portions ? 



3. State, therefore, whether green material is or is not neces- 



sary for the manufacture of starch. 



This green material in leaves is called chlorophyll (from 

 Greek chloros = green + phullon = leaf). 



32. Is carbon dioxid necessary for starch manufacture in 

 leaves? Laboratory Study No. 17. 



Secure two vigorous potted plants, two bell-jars large 

 enough to go over the plant and pot, and two trays or other 

 receptacles having a greater di- 

 ameter than that of the bell-jar. 

 Place the plants in darkness for 24 

 hours at least, so that the leaves 

 may be free from starch (see 30 

 above). Now test the leaves of 

 both plants to make sure they 

 are free from starch. Into one 

 tray pour a quantity of lime water 

 and into the other tap water. 

 Put the plants on supports of 

 some kind so that the pots will 

 not touch the liquid, and cover 

 with the bell-jars. (See Fig. 3.) 

 Be sure that the edges of the bell- 

 jars are covered with the liquid, 

 so that no air can enter the jars. Place both preparations 

 where the plants can get no sunlight for 24 hours in order 

 to give time for the absorption of carbon dioxid in the jar 

 with the lime water. Place both preparations in strong 

 sunlight for several hours. 



FIG. 3. Apparatus for demon- 

 strating the relation of carbon 

 dioxid to starch manufacture. 



