Vegetable Assimilation and Respiration. 



319 



increasing rate, at first, is followed by a uniform rate so that a curve like a 

 CO2 light limiting factor curve is produced. Knowing that the light limiting 

 value is much higher, we cannot put this simple interpretation on the result. 

 It must be remembered that it took four hours to carry through the series B 

 to F, so that a time factor of some sort may be responsible for nullifying the 

 direct effect of the stronger acids. It may be noted that in the Experiment 

 table on p. 318 the acidification effect on C had fallen to nil in about two 

 hours time, though this is not usually so. There was no opportunity of 

 continuing the investigation and analysing out the factors that contribute to 

 give the curve of fig. 11 its particular form. 



-tct^ a£^wA^c^dG^f^^^/^^m^/M^^^^sc£^ 



tale, due. Co o'liffCTicU/ CO^^ a/cm& 

 t 



10 II 



i a34567J9 

 Q-cldLLlTv^: uAitt = O'Oooi Tiormctt HCl. 



Fig. 11. — Effect of increasing acidity on bubble rate with Elodea. The data are taken 

 from the experiment set out in fig. 10. It will be seen that, at the critical part of 

 the curve, the data are not adequate to determine whether the points lie on a 

 continuous curve or on two intersecting straight lines. 



Part III. — COiMPARISON OF ASSIMILATION EaTES IN SOLUTIONS OF CARBONIC 



Acid and of Sodium Bicarbonate. 



Though several workers have studied the rate of bubbling of water plants 

 in solutions of bicarbonates, no one has compared these rates of bubbling with 

 the rates in known solutions of carbonic acid. With the aid of a bubbler and 

 bubbling cup described in Part I, comparisons between different solutions can 

 readily be made with the same plant, as a uniform bubble size is assured, 

 whether the plant is in a solution of carbonic acid or of bicarbonate. 



The results of Angelstein (1911), who observed bubble rates in a solution of 

 bicarbonate which he gradually increased in concentration, are very obscure, 

 especially because in all cases he chose to add CO2 to the water before 

 beginning the series of bicarbonate strengths. 



For determining what strengths of CO2 solutions are equivalent, in 



