296 PLANT PHYSIOLOGY 



Materials Consumed in Respiration. — -It was formerly held 

 that the part of the cell which was respired was the protoplasm 

 itself. Although carbohydrates and fats are the chief energy 

 sources of the plant, the idea was prevalent that the protein was 

 decomposed into a carbon-oxidizable portion and nitrogen. The 

 carbohydrates and fats then united with this nitrogen to produce 

 more protein which was in turn incorporated into the living mate- 

 rial of the organism and respired. According to this conception, 

 the supply of non-nitrogenous materials was gradually diminished 

 while the supply of protein material remained unchanged, even 

 though it was continually being oxidized, until the carbohydrate 

 reserves were exhausted. Only when the proteins and protoplasm 

 were no longer capable of regeneration was a decrease in the pro- 

 teins to be expected. This conception was based largely upon 

 the fact that respiration is especially active in young, growing 

 tissues rich in protein; but it has been found untenable. 



It is now held that the carbohydrates and reserves of fats are 

 used up as such without first being incorporated into proteins or 

 protoplasm. They are the chief sources of energy, and only when 

 they are exhausted, are the proteins which form the chief source 

 of the protoplasmic materials drawn upon. The proteins form 

 the materials of the engine while the ternary compounds are the 

 fuel. As in all engines, there is some wear and tear on the machin- 

 ery which, in this case, is at the expense of the proteins. Germi- 

 nating seeds lose their protein stores because the protein is being 

 rapidly transformed into the protoplasm, which is needed in large 

 quantities by the many cells produced at this time of active growth 

 and cell formation. The total amount of nuclear protein, i. e., 

 protein in the indigestible condition as found in the protoplasm, 

 actually increases during the germination of seeds according to 

 Palladin (1899). The amount of respiration may also vary with 

 the protoplasm present because the oxidizing enzymes are pro- 

 duced through the activity of the protoplasm. 



The Carbon Dioxide-Oxygen Ratio. — In considering the effects 

 of external and internal conditions upon respiration it is necessary 

 to keep in mind the difference between an effect upon the rate of 

 respiration and the effect upon the carbon dioxide-oxygen ratio or 

 respiratory quotient. As shown by the respiratory equation for 

 carbohydrates, the ratio is ordinarily one, i. e., there is a molecule 

 of carbon dioxide given off for every molecule of oxygen taken in, 



