Vegetable Assimilation and Respiration. 



323 



recorded. The points for A make a smooth sequence, but do not lie in a 

 straight line : as the concentration increases, the bubble rate declines some- 

 what from direct proportionality. Whether this is a primary relation or is 

 only an expression of the inflection of the curve, at the highest value, into 

 its horizontal course has not yet been investigated. 



•X -3 •4- 



foNaHCO^ In soLu.bio-n.. 



Fig. 15. — Rate of bubbling in sodium bicarbonate solutions of different concentrations. 

 For both curves, light = 3'5. Curve A, one plant in five solutions of increasing 

 strength ; Curve B, another plant in five solutions covering a -wider range. B shows 

 a typical limiting factor curve, but A stops just where the horizontal limb would 

 be expected. 



Figs. 14 and 15 together enable us to compare the strengths of carbonic 



acid and sodium bicarbonate that jvM sufhce to give the full effect that is 



potential in light of 3'5 units. These comparable values are given by the 



inflection points of the two B curves, both of which are for 3'o Kght. 



Whereas 0'9 volumes of CO2 per cent, is the critical value for CO2, it is seen 



that 0'32 grm. IN'aHCO.s per cent, is the corresponding value for bicarbonate. 



rr,, . .1 £ i. • 1 I.- ctn. bicarbonate ^.^ - 



This provides us with our nrst equivalence ratio, = U'oo. 



ctn. CO2 



This comparison is made very indirectly with two different plants at different 

 times, and the location of the supposed inflection point is only got by inter- 

 polation. Direct comparisons set out in the next section show that 0'29 is a 

 better value for this ratio. 



The experiments described in this section, though not very searching, 

 suffice to establish that for different concentrations of bicarbonate the bubble 

 rates, if not in absolute direct proportion to the concentration, approximate 

 closely to this relation, especially over a short range of concentrations. 



VOL. XCII. — B. 



2 B 



