1893.] The Gases in Living Plants. 99 
rapidity in healthy cells, but is entirely checked upon the 
withdrawal of light, or when it reaches a certain low intensity. 
Of course it never takes place in roots, flowers, the central 
portion of large stems, or other parts which are not green, nor 
in any fungi or other plants not possessed of green coloring 
matter. 
VARIATION IN AMOUNT DUE TO RESPIRATION. 
The other great cause of disturbance in the relation of oxy- 
gen and carbon dioxide in the plant, is the process of respira- 
tion. 
Respiration in plants is essentially the same as in animals, 
and consists in the fixation of oxygen and the liberation of 
carbon dioxide. It takes place in every living cell, whatever 
the kind of plant, whatever the part of the plant, and what- 
ever the conditions of active existence. The rate of respira- 
tion varies with the temperature, the age of the cell, and the 
nature of the chemical transformations. In normal respira- 
tion the amount of oxygen absorbed is approximately the 
same as the amount of carbon dioxide evolved. There are, 
however, certain modified forms of respiration in which this 
does not hold true. 
If living plants be placed in a vacuum, or in an atmosphere 
deprived of oxygen, it is found that they can still carry on 
life processes for some time, accompanied with an evolution 
of carbon dioxide. The oxygen necessary for this process is 
obtained from the breaking up of compounds in the cells, and 
it is therefore called intramolecular breathing. > 
The germination of seeds, which contain a large amount of 
oil, is somewhat the opposite of this last process. In order 
to convert the fat into a more directly servicable food material 
for the plant, a large amount of oxygen enters into the new 
combination, for which there is no equivalent amount of gas 
liberated. It consequently comes about that oily seeds in ger- 
minating absorb a far larger amount of oxygen than they 
liberate of carbon dioxide. This is known as vincular 
breathing. - 
