12 



in hydrogen. It is seen tliat in these two experiments the pro- 

 duction of carbonic acid in an atmosphere of nitrogen or 

 hydrogen, i.e., in the absence of oxygen, is not far behind that 

 in air, or in other words anaerobic respiration is not much less 

 than aerobic. 



Experiments were made with two varieties of ripe grapes,* 

 and gave the result that respiration was as active m nitrogen 

 and hvdroffen ass in air, more so in fact in some cases. One of 



m 



ammes 



6-2 in nitrogen, and 7-3 in hydrogen. The other experiment 

 (34 hours at 37*^ C.) gave 9-9 in air, 9-5 in nitrogen, and 10-2 in 

 hydrogen. 



The above experiments show that in ripe fruits at 30^ C. 

 anaerobic respiration may be as rapid as aerobic, or not much 

 less so- 



An experiment was also made with unripe fruit, and this 

 showed a different behaviour. Green peaches, about half grown, 

 gave off 13-4 mg. of carbonic acid per 100 grm, of fruit per 

 hour in air, 6"4 in nitrogen, and 6-1 in hydrogen. f Here the 

 anaerobic is only about half the aerobic respiration. The 

 difference between this ratio and those in the previous experi- 

 ments may be attributed to the presence of growing tissues in the 



unripe fruit . 



Germinating wheat was chosen as another example of actively 

 growing tissue, and gave a similar result to the green peaches 

 m one casej namely, 12-8 mg, in air, 6-0 in nitrogen, and 6'5 in 

 hydrogen. In a second experiment § there was a much greater 



amount 



mg 



7-8 in nitrogen, and 6'4 in hydrogen.il 



It appears then from the different experiments that ripe fruit 

 differs from unripe fruit in its respiratory processes, respiration 

 in the former being to a great extent independent of an external 

 supply of oxygen, while in the latter about half the respiration 

 is stopped in the absence of oxygen. This is regarded as indi- 



maintained 



most part by enzymes 



while in unripe fruit the respiration is partly of the same nature, 

 but is as much due to processes dependent on the presence of 



* Sterilised in alcohol. 



+ The experiment was run for 90 hours at 30^ C. ; the peaches were jiot 

 sterilised. 



J The experiment lasted 81 hours at 25° C. Previous experiments have 

 shown that in germinating wheat intramolecular fanaerobic) respiration is 

 much less than normal respiration, and this appears to be generally the case 

 in aerobic plants. There are exceptions, however, seedlings of the broad 

 bean and the castor-oil plant having been found to respire equally with and 

 without oxygen. 



§ 83 hours at 25° 0. 



jl In the first of these two experiments the seeds had been sterilised in 

 alcohol, and in formalin in the second. Hence it appears that one of the 

 sterilising agents must have penetrated a little too far and affected the 

 living tissue. Either the alcohol-treatment Retarded respiration, or the 

 formalin increased it. 



