CHAPTER II. 
THE SEED AND GERMINATION. 
PRELIMINARY. 
Before dealing with the seed itself it will be 
necessary to learn how to test certain substances it 
contains, and to identify two gases, one needed for 
germination, the other produced thereby. 
Oxygen may be prepared by heating in a test tube 
about a quarter of a teaspoonful of chlorate of potash 
mixed with a very small quantity of black oxide of 
manganese. After sufficient heating, a glowing 
splinter of wood plunged into the tube will burst into 
flame. Taking it for granted that the substance given 
off is oxygen, we have discovered the following facts. 
‘Oxygen is a colourless gas without taste or smell, and 
vigorously supports combustion. The fact that sub- 
stances burn in ordinary air, though not so violently 
as In pure oxygen, would naturally lead us to suppose 
that the air is diluted oxygen. As a matter of fact, 
in five gallons of air we have about one gallon of 
oxygen, diluted with about four gallons of an inactive 
gas called nitrogen. Eight-ninths of the weight of 
water is also oxygen. Oxygen is a very active gas, 
combines readily with a great many substances, and, 
in the act of combination, gives off heat. This com- 
bining of oxygen with some other substance is called 
oxidation, and the substance with which it combines 
is said to be oxidised. Under certain circumstances, 
the oxidation may be very violent and produce, at a 
civen moment, much heat and light. In such cases we 
all it burning. When coal burns in a fire we have this 
fierce oxidation. The oxygen of the air combines with 
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