78 THE MAKING OF THE LIVING MATTER 



deep gluNS jar containing tVesli 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 bu})bles 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 



^1''' , ^i'.ljlK^ , , the presence of oxygen. A sim- 



^B^E^StBjii^' pier but less accurate experiment 



c:^^^^^^^^ is ^^ immerse an active leaf of a 



-^H^hH^^ ^^'^ter plant, and to observe the 



|BB^^- .. bubbles which arise. From a 



^^HjP^"' JHmm§- leaf in sunlight the bubbles often 



^^Kf ^^K" arise in great numbers; but from 



^^^^^^^^^^^^' one in shadow, the bubbles usu- 



"~^ - ^" ^ ' ally are comparatively few. Fig. 



U2. To show that a leaf may 112. Somc of the bubblcs may 



give off oxygea. |,g ^j^jy ^^^ ^ 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 lecwes of plants which 

 have been exposed to sunlight; tut 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 



