70 



ACIDITY AND GAS INTERCHANGE IN CACTI. 



dent that the absorption of oxygen, rather than the evolution of carbon diox- 

 ide, is influenced. The effect of temperature change on the activity of young 

 joints is brought out in experiments 39, 39 a, b, and c (table 60). The first 

 two were carried on at 24 C., the others at 34 C. In this case the identical 

 material was used in all four experiments. The averages are given in table 45. 



TABLE 45. 



The -Q- quotient rose during the experiments from 0.83 to 0.90, but it is 



not that point which is of present concern. There would normally be a rising 

 ratio with falling acidity, which is perhaps accentuated in this case by the rising 

 temperature as well. As for the amount of carbon dioxide given off, there is 

 an increase of over 100 per cent at the higher as compared with the lower 

 temperature. 



While, as has been shown in the pages on acidity, increase of temperature 

 is accompanied by decrease in acid-content, it is not to be expected that the 

 averages taken from the whole mass of miscellaneous experiments, the material 

 for which was collected under varying circumstances and from plants of very 

 diverse acidity, would give any decisive evidence in this direction. A high 

 acidity which is falling will give a relatively high ratio between the oxygen and 

 carbon dioxide, irrespective of temperature, while the reverse is true with a low 

 acidity that is rising. Thus, while temperature influences the ratio it is not so 

 important a factor as is the acidity or the age or condition of the material. 



By selecting a series with a fairly limited range of acidity the temperature 



CO 



effect on the -Q-* ratio becomes apparent. Taking from the experiments with 



mature-turgid joints the ratios in which the material showed an acidity value 

 ranging between 1.01 and 2.00 c.c. and also those between 3.01 and 4.00 c.c., 

 N/10 KOH per gram dry weight, the results are as follows: 



TABLE 46. 



