RESPIRATION AND FERMENTATION 135 



its transformations clear to the proteid and to the chyle and tissues 

 0) animals) so long as it can be kept from oxidation, and how 

 this energy may be transformed from energy of position to energy 

 of motion at any desired point when oxygen is allowed to unite 

 chemically with the carbon. He will be aided by an understand- 

 ing of the phenomena of carbon combustion, of the action of 

 storage-batteries, and even by so crude a physical analogy as 

 the storage of speech in the phonograph. It is only through an 

 understanding of these processes that he will be able to appre- 

 ciate the fundamental significance of respiration in the life of 

 organisms. 



The foregoing experiments have led more than once near to a 

 consideration of the effects of external conditions upon respiration. 

 For some of these the difficulties of experimental study are con- 

 siderable. But for one of the most important, temperature, an 

 experimental study is possible as follows: 



Suggested Experiment. In the chambers of a differential thermo- 

 stat, an instrument described later under Growth, place simple and similar 

 respirometers, each containing the same weight of respiring seeds and the 

 same strength of caustic potash. Run the instrument with a range of tem- 

 perature from 25°-35°, and observe the comparative respiration as meas- 

 ured by the rate of rise of the reagent. 



Optimum Temperature for Respiration. It is agreed by all observers 

 that the rate of respiration increases with the rise of temperature to near 

 the death point, the optimum thus lying very close to the maximum. Hence 

 in theory, where respiration alone is under study, the higher temperatures 

 give quickest results. But as the higher temperatures influence other func- 

 tions of the plant unfavorably, it is in practice better to keep the tempera- 

 ture lower, and the practical optimum may be taken as 28°. 



Closely correlated with respiration is the consideration of 

 the free access of oxygen and removal of carbon dioxide, a sub- 

 ject which will be considered later under Absorption. 



Among the various respiratory ratios shown by different 

 seeds earlier studied, the student will have met with some {e.g., 

 peas and other legumes) which show a release of carbon dioxide 

 out of all proportion to the amount of oxygen absorbed, imply- 

 ing that oxygen must in those cases be supplied from some 

 source other than the air in the instrument. This at once raises 



