Vegetable Assimilation and Respiration. 



325 



but C and D for 0'2 per cent, bicarbonate gave 2'5 and 3*0 b.p.m. respectively. 

 A third sample, E, agreed with D in giving 3-0 b.p.m., and this rate, or the 

 average of 2'8 b.p.m., may be adopted for 0-2 per cent, bicarbonate. 



In fig. 17 are set out the data in evaluating the effect of a weaker bicar- 

 bonate solution. The rate in 0"6 per cent. CO2 is 7'1 b.p.m., while in 

 0-08 per cent. NaHCOs it becomes 3'3 b.p.m. Fig. 18 presents the results 

 with another strength of bicarbonate. Here duplicate solutions were used 

 and the rates adopted were the quicker rates in B and D, namely, 3"8 b.p.m. 

 in 0'6 per cent. CO2 and 4'1 b.p.m. in 0"166 per cent. NaHCOa. 



The bubble rates established for these three pairs of solutions are set out 

 in the adjoining Table, as well as the adopted rates from two other experi- 

 ments, which were rather irregular in some details. 



The first use we can make of this set of ratios is to calculate from the CO2 

 solutions what should be the CO2 concentrations in the bicarbonate solutions, 

 assuming that direct proportionality holds between rate and concentration in 

 CO2. For the first case, the calculated CO2 concentration of the bicarbonate 





Assimilation in CO2 

 solutions. 



Assimilation in 

 bicarbonate solutions. 



Estimated COj concentration per- 

 centage in bicarbonate solutions. 



Experiment. 





























P.c. con- 

 centration. 



Bubble 

 rate. 



P.c. con- 

 centration. 



Bubble 

 rate. 



By assimila- 

 tion rates. 



Physico-cbemically 

 (extreme values). 





0-60 



7-1 



0-08 



3-3 



0-28 



-24-0 -28 



b 



-30 



-5 



0-10 



-5 



0-30 



-31-0 -36 





0-385 



4-0 



-10 



3-5 



0-34 



0-31-0 -36 



d 



0-60 



3-8 



-166 



4-1 



0-65 



-53-0 -60 





-60 



2-4 



0-20 



3 



0-75 



-64-0 -72 







solution equals 0'6x3-3/7'l = 0*28 per cent. CO2. The similarly calculated 

 values for all the other cases are set out in column 6. On this follows the 

 question whether the CO2 concentrations thus indicated biologically agree 

 with the data derived from physico-chemical work on bicarbonates. Informa- 

 tion on this point I owe to Dr. F. F, Blackman, who is dealing with this 

 matter in another paper; he has supplied the numbers of the last column 

 in the Table. These represent the extreme possible values of the CO2 con- 

 centrations in the freshly made bicarbonate solutions used in these experi- 

 ments. The ambiguity in these values is due to some of the constants 

 involved in the calculation being insufficiently determined. 



It will be seen that biological results align quite well with the physico- 

 chemical, being close enough to establish the view that the rate of assimila- 

 tion and bubbling in dilute bicarbonate solutions is due entirely to the 

 concentration of carbonic acid that arises spontaneously by decomposition of 



