Leaves. 



79 



r^ 



kind of water that the tube holds. Expose all three prepa- 

 rations to the full light of the sun. Compare the results 

 with those obtained from a single plant placed successively 

 under the three sets of conditions. 



The first tube and beaker will contain a moderate 

 amount of carbon dioxide, the second little or none, and 

 the third a great deal. Watch for bubbles of gas issuing 

 from the cut ends of the branches. Count the number 

 rising from each in a given unit of 

 time. The green leaves are taking 

 carbon dioxide from the water and 

 are dissociating the carbon and oxy- 

 gen, retaining the carbon for the 

 manufacture of starch, and liberat- 

 ing part of the oxygen. The fre- 

 quency of bubbles in each tube is 

 an indication of the relative amounts 

 of starch manufactured. Set the 

 tubes in the shade and note the 

 effect. What do you learn from 

 these experiments as to the con- 

 ditions necessary to the manufac- 

 ture of starch in the leaves .■' 



Nearly fill a glass funnel with 

 shoots of Ceratophyllum, Myrio- 

 phyllum, or other suitable water plant, and invert it in a tall 

 beaker of well or spring water. The end of the stem of the 

 funnel should be submerged for an inch or more. Fill a 

 test tube with water and invert over the funnel (see Fig. 30). 

 Set the preparation in the sunlight. If the tube becomes 

 nearly half filled with gas, carefully remove the tube from 

 the funnel, close the tube tightly with the thumb, while its 

 mouth is kept submerged; turn its mouth upward, remove 



Fig. 30. 



Device for collecting the gas 

 evolved by a green plant un- 

 der the influence of the sun- 

 light. See text. 



