78 



THE MAKING OF THE LIVING MATTER 



112. To show that a leaf may 

 give off oxygen. 



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 elow 



with a brighter flame, showing 

 the presence of oxygen. A sim- 

 pler but leSs accurate experiment 

 is to immerse an active leaf of a 

 water plant, 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 usu- 

 ally are comparatively few. Fig. 

 lib. Some of the bubbles may 

 be only air, particularly if 

 marked changes in temperature occur. Observe the bub- 

 bles 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 he 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 



