96 GERMINATION OF SEEDS: SEEDLINGS 
during their development. But the transformation of foods into 
the various structural elements of the plant involves chemical 
reactions which take place only when there is energy supplied. 
This brings us to another process called respiration by which the 
energy required for the chemical changes involved in changing 
foods into cell walls, protoplasm, and other structures is secured. 
Respiration in plants, just as in animals, is an oxidation process 
in which some food or other elements are burned, as we commonly 
say, with the result that oxygen is required and energy, carbon 
dioxide, and water vapor are produced. Respiration occurs only 
within the cell in connection with which it will be more fully dis- 
cussed. But since there is no place where respiration is more in 
evidence than in germination where the cells are extremely ac- 
tive, some of its features should be noted in connection with that 
process. Furthermore, much about germination can not be un- 
derstood unti] something is known about respiration. 
Cells, like an electric motor, steam engine, etc., can not do work 
unless they have energy. Some cells, like the green cells of leaves, 
are able to utilize the sun’s energy for some kinds of work; but 
when cells are not specially provided with pigments for utilizing 
the sunlight, they have to depend entirely upon the energy 
which they produce within themselves. In the sugar and other 
foods of the seed there is much latent energy which can be 
released as active energy by oxidizing these substances, which 
are thereby broken into simpler compounds of which carbon diox- 
ide and water are the simplest and most noticeable ones. It is 
this oxidizing of substances, so that their stored energy is re- 
leased, that constitutes respiration, which necessarily must be 
accompanied by a consumption of oxygen and the production 
of simpler compounds. It is now clear why seeds do not ger- 
minate well when oxygen is excluded as the experiment in Figure 
91 demonstrates. Although most of the energy released is used 
in carrying on the work of the cell, some, however, escapes as 
heat, which, like the liberation of carbon dioxide and water vapor, 
indicates that respiration is going on. 
Respiration in seeds is easily demonstrated by germinating 
seeds in a closed jar, in which the production of heat and carbon 
dioxide with the accompanying loss of oxygen, and the accumu- 
lation of moisture can be demonstrated. By germinating seeds, 
such as Peas or Beans, in a closed vessel in which a thermometer 
