GAS INTERCHANGE. 81 



second showed a considerable fall. The gas ratio of the latter was noticeably 

 higher. Similarly in series 33 (table 59) the ratio was higher in the first one 

 of the set, where the acidity was falling, than it was in 336 where an increase 

 in the acid-content was found. In the middle experiment, 33a, where a slight 

 rise in acidity is indicated, it is true that the ratio is nearly as high as in 33, 

 but an exact mathematical correspondence is hardly to be anticipated. Also 

 in series 34 (table 59), the rising acidity in 34 itself gave a lower ratio than 34a, 

 where the amount of acid diminished. The last one of this set, 346, had an 

 acidity which remained stationary, the ratio again low, though somewhat 

 higher than in the first experiment. In all of these cases the acidity was 

 relatively low and the rise or fall was not very great. It was difficult, at least 

 under the conditions of experimentation, to obtain a very great rise in acidity 

 during the time of the experiments, which was usually not over 2 hours. In 

 general, acidity rises more slowly than it falls, certainly when the diminution 

 of the acid occurs in tissue where the initial accumulation is considerable. 



In experiments 12 and 12a (table 58) we have a case, however, where the 

 acidity was at a very low point, yet showed a marked increase. These two 

 experiments are comparable, for the material came from different branches of 

 the same plant, and they were carried on at the same time. The acidity was 

 rising in both, but it reached a higher point in 12a than in 12, almost doubling 

 itself in the 2 hours during which the experiment was in progress. The ratio 

 of experiment 12a was very much lower than of experiment 12; indeed, it was, 

 as has already been pointed out, the lowest ratio obtained. In experiment 12 

 the rise in acidity amounted to 37 per cent and the ratio was 0.50; in 12a, 

 where the rise was 87.5 per cent, the ratio was 0.29. The initial acidity was 

 practically the same in both cases. 



Hence it is evident that during the process of the accumulation of acid in 

 the tissue, much less carbon dioxide is given off in proportion to the amount 

 of oxygen absorbed, or vice versa. This statement is further supported by an 

 examination of those experiments in which the initial acidity was high and 

 falling (tables 60 and 61). In those where the gas interchange is going on at 

 the most rapid rate, which means that the evolution of carbon dioxide is at 

 its maximum, the ratio is of necessity higher. The group of experiments 

 numbered from 39 to 39c (table 60) makes this especially clear. The first two 

 in this series were carried on at the temperature of 24 C., and, while the fall 

 in acidity was considerable, it was much less than in the other two, where the 

 temperature was from 31 to 32 C. The ratio in the first case was 0.83 and 

 in the latter was 0.90. In every instance where the gas-interchange rate is 

 high, which means also a high acidity that is ready to fall under even a slight 

 stimulus, the ratio is also high. In other words, while more oxygen is absorbed 

 with falling acidity under these conditions, the absorption does not keep pace 

 with the increased evolution of carbon dioxide, so that the ratio naturally 

 approaches more nearly to unity, or even at times exceeds it. 



If general averages are compared, the following results are obtained: In 27 

 experiments, all of which showed acidity that was diminishing, the average 

 ratio is 0.90, with a total dry-weight acidity at the beginning of 4.50 per gram 

 and of 3.16 per gram at the end. On the other hand, 21 experiments with 

 material of low initial acidity that was on the increase gave an average ratio 

 of 0.59 and an initial acidity of 1.44 per gram rising to 1.85. Whether looked 



