GERMINATION AND GROWTH 31 



a glass rod to mix it with the gas in the larger jar. Has the limewater in 

 the control experiment undergone the same change? (It may show a 

 slight niilkiness due to the carbon dioxide in the air.) Insert a thermom- 

 eter among the seeds in both of the larger jars, and compare their tem- 

 perature with that of the outside air; which shows the greater rise? 

 From this experiment and the last one, what process, common to animals, 

 would you conclude has been going on in the germinating seeds ? 



Note. — Heat in germinating seeds is not always due to this cause 

 alone, but is sometimes increased by the presence of miimte organisms 

 called bacteria. Germinating barley and rye in breweries sometimes 

 show an increase in temperature of 40 to 70 degrees, due to these organisms, 

 and spontaneous combustion in seed cotton has been reported from the 

 same cause. 



27. Oxidation. — The process that brought about the 

 results observed in the foregoing experiments, and popularly 

 known as combustion, is more accurately defined by chemists 

 as oxidation. It takes place whenever substances enter into 

 new combinations with oxygen. The most familiar examples 

 of it are when oxygen enters into combination with substances 

 containing carbon. It was the union of a portion of the 

 oxygen of the air in Exp. 21, and of that in the tube in Exp. 

 22, with some of the carbon in the wood, that caused the 

 burning. The effect was more marked in the second case 

 because the oxygen in the tube was pure, while in the air it 

 is mixed with other substances. 



28. Carbon. — The black substance left in your hand 

 after oxidation of the wood in Exps. 21 and 22 is carbon. 

 It composes the greater part of most plant bodies, and, in 

 fact, is the most important element in the realm of organic 

 nature. There is not a living thing known, from the smallest 

 microscopic germ to the most gigantic tree in existence, that 

 does not contain carbon as one of its essential constituents. 



29. Carbon dioxide. — The gas produced by the burning 

 candle in Exp. 23, by the germinating seeds in Exp. 25, and 

 expelled from your own lungs in Exp. 24, is carbon dioxide. 

 Chemists designate it by the symbol CO2, which means that 

 it consists of one part carbon to two parts oxygen. It is ar 



