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 milkiness 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? 
Nore. — Heat in germinating seeds is not always due to this cause 
alone, but is sometimes increased by the presence of minute 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 CO,, which means that 
it consists of one part carbon to two parts oxygen. It is an 
