GAS INTERCHANGE. 79 



all. In K' the ratio sank to 0.02 and in DD' to 0.05, for, although the absorp- 

 tion of oxygen was about normal, the carbon dioxide given off was very slight. 

 The acidity conditions in K', which was with mature-turgid material both as 

 to pure juice and total acidity, were not noteworthy, being neither very high 

 nor very low. In the second case, the material of which was young, the acidity 

 was high in the beginning, but fell off to a very great extent at the end. In 

 this experiment, which ran for only \\ hours, the acidity, both in juice and in 

 total amount present, fell to less than an eighth of its initial figure. This was 

 the greatest drop noted in so short a time. In the face of what all other experi- 

 ments with falling acidity show, this is hard to understand, for it is to be 

 expected that when the acid is diminished there would be a large evolution of 

 carbon dioxide. 



In the three other experiments, in which no carbon dioxide at all was found, 

 the acidity varied. In Q' with young material it was relatively high, and rose 

 somewhat during the course of the experiment. In the other two instances, 

 where flaccid material was employed (experiments 1 and 17), the acidity was 

 low in experiment 1 very low. As regards acidity, these results are conflict- 

 ing and no conclusion can be drawn from them. However, as there was no 

 adequate reason for excluding them, they were accepted, but have not been 

 used in the general averages that have been discussed. It is possible that some 

 unknown experimental condition affected the carbon-dioxide evolution. It 

 does not seem probable that the results have important significance, and no 

 further mention of them will be made. 



RELATION OF GAS RATIO TO COURSE OF ACIDITY. 



Of all the series of experiments, those carried on during the summer of 1913 

 are the most interesting. In these, as well as in a few conducted during the 

 previous summer, the acidity of the material was determined at the beginning 

 of the experiment (initial acidity) and also at the end (final acidity). Since 

 determining the acid-content necessitates the destruction of the tissue, it was 

 impossible to determine the initial acidity from the same specimen that was used 

 for gas interchange. Consequently parallel material was employed which 

 came from the same plant at the same time and from as nearly as possible the 

 same region. The final acidity was always obtained from the specimens 

 actually employed in the gas-interchange experiment. By this means, the 

 important point as to whether the acidity was rising or falling could be deter- 

 mined with tolerable certainty. The acidity of different plants has been 

 found to be very different, but the acidity of neighboring parts of the same 

 plant, where the tissues are of the same age, is closely similar. Table 52 gives 

 the averages for these experiments. It brings out conspicuously that with low 

 acidities that are rising the gas ratio is usually low, while with high acidities 

 that are falling the ratio approximates unity. This fact has been hinted in 

 several places in this paper, but no detailed consideration of these important 

 points has as yet been made. 



c^o 

 In the first group there is but one experiment which gave a -^p quotient of 



0.29, with a total acidity that rose to nearly double the original amount during 

 the course of the experiment (experiment 12a, table 58). The material used 

 was a young joint in active growth; but, despite this, the acidity was low, the 



