‘PLANT PHYSIOLOGY 141 
in the form of heat. In living beings, a similar process 
takes place, but the rise in temperature is very small, 
and the process of combustion is a slow one. In plants 
the organic material obtained by assimilation is con- 
sumed, carbon di-oxide being set free, and oxygen being 
absorbed. Thus respiration is, to a certain extent, an- 
tagonistic to assimilation and the two processes may be 
contrasted. 
Respiration. 
1. Oxygen is taken in, and 
earbon di-oxide is liber- 
ated. 
2. Energy is set free. 
3. Takes place in all parts 
Assimilation. 
Carbon di-oxide is taken in 
and oxygen is liberated. 
Energy is stored up. 
Takes place only in green 
parts of the plant and 
only in the sunlight. 
of the plant at all times. 
In the daytime assimilation is far more active than 
respiration, hence in any experiments with green plants 
it is necessary to place them in darkness, in order to de- 
tect their respiration, as in the daylight the carbon di- 
oxide evolved in respiration is at once re-absorbed by 
assimilation. 
114. Experiment 18.—Place some germinating peas 
on damp cotton-wool in a jar, and cork it up. Set up 
a similar jar without the peas asa control. Test the 
air in both jars at the end of twenty-four hours by 
putting a lighted match in each, and also a little lime- 
water. 
115. Experiment 19.—Obtain three large jars with 
corks, and place a little lime-water ineach. Hang a 
large leaf by a thread from the corks of two of the jars, 
