riioiosVM iiKsis 67 



B. Let an entire leaf of each kind remain for some hours in a 

 warm, sunny place and notice the comparative amount of 

 wilting in both cases. Explain. 



Refkhkncks. Kerner-Oliver, 2; Haberlandt, 33; Schimper- 

 Fisher^, 56; Warming-Graebner, 57. 



EXPERIMENT XXXI 



Oxygen making in sunlight. * * Place a green aquatic plant in 

 a glass jar full of water, at about 70° F. (21° C), in front of a 

 sunny window.^ Note the formation of oxygen bubbles looking 

 silvery by reflected light.^ Remove to a dark closet and after 

 fifteen minutes examine by lamplight, to see whether the rise of 

 bubbles still continues. 



This gas may be shown to be oxygen by collecting some of it 

 in a small inverted test tube filled with water and thrusting 

 into it the glowing coal of a match just blown out. It is not, 

 however, always very easy to do this satisfactorily. 



Repeat the experiment, using water which has been well 

 boiled and then quickly cooled in a tightly covered vessel. 

 Boiling removes all the dissolved gases from water (including 

 much carbon dioxide), and they are not redissolved in any 

 considerable quantity for many hours. 



References. Detmer-Moor, 9 ; Darwin and Acton, 11. 



EXPERIMENT XXXII 



Occurrence of starch in nasturtium leaves.* * Toward the close 

 of a very sunny day collect some bean leaves or leaves of nastur- 

 tium (TrojHvolum). Boil these in water for a few minutes, to kill 

 the protoplasmic contents of the cells and to soften and swell 

 the starch grains. Soak the leaves, after boiling, in strong, hot 

 alcohol for half an hour, to dissolve out the chlorophyll, which 



1 FJodea, yfyriophylliDn, ('hriisnspjcii'mm, Potainogeton, any of the preen 

 aquatic tlowcriu"; plants, the a(niatic moss, Fontinalis, or even the common pond 

 scum, Spiroffyra, will (h) for this experiment. 



2 Some of the earlier bnhhles may contain a good deal of air which was 

 dissolved in the water and set free as it grows warm, but the later bubbles will 

 be fairly pure oxygen. 



