192 



EXPERIMENTS WITH PLANTS 



morning and continued until near sundown (the leaf 

 should receive sunshine in the meanwhile : prolong the 

 experiment two days if necessary). We then lift 

 the jar very carefully, so as not to 

 admit any air, and introduce a lighted 

 candle, as before. If it does not imme- 

 diately go out, it indicates that some of 

 the carbon dioxide has been absorbed 

 by the leaf and decomposed, with the re- 

 sult that oxygen is set free, so that 

 further combustion is possi- 

 ble. As a control use a 

 bottle with no leaf in it. 



Chemical analysis shows 

 that if carbon dioxide and 

 water unite to form starch, 

 oxygen must be given off, just 

 as we have found in this ex- 

 periment. Another way of 

 testing this matter is shown 

 in Fig. 111. A plant which 

 naturally grows submerged in 

 water is put into water in a 

 glass jar and placed in sun- 

 light. The gas evolved is col- 

 lected in the funnel, which is 



111. Arrangement for collecting the firSt filled witll Water by Sub- 

 gas given off by a water-plant in . . , i i . . . 



sunlight. mergmg it and corkmg it 



