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 until 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 



