98 NATURE TEACHING 



caustic potash will absorb what carbon dioxide there is 

 in the bottle, and the soda lime will prevent any more 

 entering. 



Have ready two fuchsia shoots, which have been in 

 the dark for a day and have been tested, and are known 

 to be free from starch. Put the ends of their stalks in 

 little bottles of water, and place one in each bottle. 

 Replace the corks. It is best to paint the corks over 

 with a coating of paraffin wax to make sure that no air 

 gets through them. Put the bottles thus fitted up, side 

 by side, in the sunlight, and after say six hours' exposure, 

 test a leaf from each for starch in the ordinary way. If 

 there is no appreciable difference leave them for another 

 day, and test again in the late afternoon. By this time 

 it should be found that the leaves in the bottle contain- 

 ing carbon dioxide have formed starch, whilst the others 

 have not. The success of this experiment depends on 

 having well-fitted, good corks, and on the glass tubes 

 fitting tightly in the corks. Any leakage will allow air 

 containing carbon dioxide to enter, and so spoil the 

 experiment. 



In the course of our experiments we have repeatedly 

 found that if a plant with its leaves loaded with starch 

 is put away in the dark and left there for twelve hours 

 or longer (according to the kind of plant employed), the 

 starch will have disappeared. What has become of this 

 starch ? An answer to this question can also be obtained 

 by experiment, but it is necessary that we should first 

 make some preliminary experiments so that we may 

 understand what is taking place. 



Place a piece of starch in cold water and let it remain 



