20 GERMINATION OF THE SEED 



as heat, work, and formation of compounds, so in the germ- 

 inating seedling oxidation of material results in the various 

 forms of energy necessary to produce a plant. This oxida- 

 tion, or respiration as it is called, requires the presence of 

 free oxygen, and the products of combustion are carbon 

 dioxide and water in the case of starch and sugars. In the 

 case of oils, probably a sugar is first formed. Both oils and 

 carbohydrates contain carbon, hydrogen, and oxygen, but 

 carbohydrates contain a much larger proportion of oxygen 

 than do oils. It is highly probable that intermediate products 

 are formed in part before carbohydrates are completely 

 converted to carbon dioxide and water. Germinating seeds, 

 then, absorb not only water, but oxygen, and give off or 

 respire carbon dioxide and water. The water formed in 

 respiration remains for the most part in the cells where it 

 is formed, and serves as solvent water or chemical water 

 in changing insoluble compounds to soluble compounds. 

 Temperature is a very important factor in oxidation, and 

 within limits the higher the temperature the faster the 

 oxidation. 



Unlike ordinary chemical oxidation or combustion, respira- 

 tion in seeds is not a direct union of oxygen with another 

 substance. Variations in quantity or pressure of oxygen 

 have little effect on the rate of oxidation, as they have in the 

 case of true combustion. Moreover, outside of the seed, 

 substances like starch do not oxidize except at high tempera- 

 tures, and yet in the seed oxidation goes on at relatively low 

 temperatures. Oxidation in the seed is due rather to the 

 presence of certain catalytic agents, or enzymes, which act 

 as aids in making oxygen unite with seed materials. 



Oxidation in the seed causes loss of material, as might be 

 expected. In corn grain, for example, it has been noted that 

 half of the reserve food material has disappeared in three 

 weeks, due to oxidation. Energy produced by this oxidation 

 can be observed in the movements of root and plumule, 

 in the formation of new compounds, and in the production 

 of heat. A mass of seeds enclosed in a non-conducting vessel 

 has been observed to raise the temperature 5° to 10° C. 

 during germination. This production of heat in the germin- 



