944 



CONCENTRATION FACTORS 



CHAP. 27 



the mass action law, since it is related to changes in permeability and other 

 colloidal properties of the protoplasm and the cell membranes, which af- 

 fect, to a varying degree, all activities of the living cell. Dehydration ef- 

 fects were therefore discussed in chapter 13 (Volume I, page 333), where 

 we dealt with various physical and chemical inhibitions and stimulations 

 of photosynthesis. 



It was mentioned there (page 334) that one of the ways in which de- 

 hydration may inhibit photosynthesis is bj'^ its influence on the stomata. 

 Since the primary purpose of the stomata is to regulate transpiration, they 



100 



2 



o 



< 75- 



< 

 o 



50- 



< 



b 25 - 



LlI 



q: 



10 20 30 40 50 



HYDROGEN PRESSURE, mm. Hq 



60 



70 



Fig. 27.10. Effect of hydrogen pressure on rate of hydrogen assimilation by 

 Streptococcus varians (after French 1937). 114 mm.^ cells. Incandescent lamp 

 below conical vessels; 25° C; argon + 5% CO2; rate in 95% H2 = 100. 



naturally close upon dehydration (by an increase in osmotic pressure in 

 the guard cells; cf. page 912). In this way, the reduction in the activity 

 of one of the reactants in photosynthesis (water) may result in the inter- 

 ruption of the supply of the other reactant (carbon dioxide) . 



A more favorable opportunity for quantitative kinetic study arises 

 when hydrogen, hydrogen sulfide, thiosidfate or other inorganic or organic 

 substances replace water in the role of the reductant reacting with carbon 

 dioxide in purple bacteria or so-called "adapted" algae (cf. Vol. I, chapters 

 5 and 6). 



Figure 27.10 (after French 1937) shows the effect of changes in the 

 concentration of hydrogen on the rate of photoreduction of carbon dioxide 

 by Streptococcus varians. The over-all reaction in this case is, according to 

 Volume I (page 104), 2 H2 + COo ^ {CH2O} + H2O. The "hydrogen 



