78 



THE MAKING OF THE LIVING MATTER 



deep glass jar containing fresh spring or stream water, 

 place fresh pieces of the common water -weed elodea (or 

 anacharis). Invert a test tube over the stem of the fun- 

 nel. In sunlight bubbles of oxygen will arise and collect 

 in the test tube. When a sufficient quantity of oxygen 

 has collected, a lighted taper inserted in the tube will glow 



with a brighter flame, showing 

 the presence of oxygen. A sim- 

 pler experiment is to immerse an 

 active leaf of lettuce or other 

 plant in water, and to observe 

 the bubbles which arise. From 

 a leaf in sunlight the bubbles 

 often arise in great numbers ; but 

 from one in shadow, the bubbles 

 usually are comparatively few. 

 Fig. 112. The water catches or 

 holds the oxygen in bubbles and 

 thereby makes the process visible. Observe the bubbles 

 on pond scum and water weeds on a bright day. 



165. Starch is present in the green leaves of plants which 

 have been exposed to sunlight ; but in the dark no starch can 

 be formed from carbon dioxid. Apply iodine to the leaf 

 from which the chlorophyll was dissolved in a previous 

 experiment (159). Note that the leaf is colored purplish 

 brown throughout. The leaf contains starch (75). Se- 

 cure a leaf from a plant which has been in the darkness 

 for about two days. Dissolve the chlorophyll as before, 

 and attempt to stain this leaf with iodine. No purplish 

 brown color is produced. 



166. The starch manufactured in the leaf may be entirely 

 removed during darkness. Secure a plant which has been 

 kept in darkness for twenty-four hours or more. Split 

 a small cork and pin the two halves on opposite sides of 

 one of the leaves, as shown in Fig. 113. Place the plant 



112. To show that the leaf gives 

 off oxygen. 



