PLANT GROWTH AND NUTRITION 



65 



Diagram to show that when a piece of 

 wood is burned it forms water and 

 carbon dioxide. 



the air. When the oxygen of the air in the jar was used up, 

 the flame went out, showing that oxygen is necessary to make a 

 thing burn. This uniting of 

 oxygen with some other sub- 

 stance is called oxidation. 



Oxidation possible without a 

 Flame. — But a flame is not 

 necessary for oxidation. Iron, 

 if left in a damp place, becomes 

 rusty. A union between the 

 oxygen in the water or air and 

 the iron makes what is known 

 as iron oxide or rust. This is 

 an example of slow oxidation. 



Oxidation in our Bodies. — If we expel the air from our lungs 

 through a tube into a bottle of limewater, we notice the lime- 

 water becomes milky. Evidently carbon dioxide is formed in our 

 own bodies and oxidation takes place there. Is it fair to believe 

 that the heat of our body (for example, 98.6° Fahrenheit under the 

 tongue) is due to oxidation within the body, and that the work 

 we do results from this chemical process. If so, what is oxidized? 



Energy comes from Foods. — From the foregoing experiment 

 it is evident that food is oxidized within the human body to re- 

 lease energy for our daily work. Is it not logical to suppose that 

 all living things, both plant and animal, release energy as the re- 

 sult of oxidation of foods within their cells ? Let us see if this is 

 true in the case of the pea. 



Food oxidized in Germinating Seeds. — If we take equal 

 numbers of soaked peas, placed in two bottles, one tightly stop- 

 pered, the other having no stopper, both bottles being exposed to 

 identical conditions of light, temperature, and moisture, we find 

 that the seeds in both bottles start to germinate, but that those 

 in the closed bottle soon stop, while those in the open jar continue 

 to grow almost as well as similar seeds placed in an open dish would. 



Why did not the seeds in the covered jar germinate? To 

 answer this question, let us carefully remove the stopper from the 

 stoppered jar and insert a lighted candle. The candle goes out 



HUNTER, CIV. BI. 5 



