134 RESPIRATION 



The respiration of Laminaria is depressed after treatment 

 with either hypotonic or hypertonic solutions, the depression 

 being greater in the latter concentration and shows a linear 

 relationship. With hypotonic solutions the relation between 

 concentration and respiration is more complex. In Chlorella 

 the respiration is depressed on exposure to hypertonic solutions : 

 if the period of treatment is short, the original rate of respira- 

 tion is attained on removal from the solution ; if the exposure 

 is prolonged, the respiration rate does not rise to the original 

 level after removal from the solution, a permanent change in 

 the organism has been effected, a lowering of the rate of meta- 

 bolism. Since the concentration of the surrounding solution 

 has effect on the water content of the tissues, this aspect is 

 clearly connected with the relationship of respiration and 

 water content. 



The use of mixtures of salts also accelerate or retard 

 according to the degree of their antagonism : thus the normal res- 

 piration rate of Aspergillus niger in a culture medium containing 

 19 c.c. of -5M sodium chloride and I c.c. of ^M calcium chloride 

 is maintained, although each of these salts in these concen- 

 trations and acting alone will accelerate respiration.* The 

 chlorides of magnesium and sodium, of sodium or potassium 

 and calcium exhibit a conspicuous antagonism, whilst the 

 chlorides of magnesium and calcium and of sodium and potas- 

 sium are antagonistic but slightly in their effect on respiration. 



ACIDITY. 



The degree of acidity of the cell sap shows much variation 

 and is an expression of the physiological condition and of 

 particular metabolism. Thus the acidity of anthocyanin 

 containing leaves may be double that of green leaves of the 

 same species, and the acidity of fleshy plants is greater by 

 night than by day. 



In some plants the hydrogen ion concentration may 

 profoundly modify the respiration intensity ; Nitrosomonas, 

 for example, shows the greatest rate of respiration in a medium 

 in which thepH value is between 8-4 and 8-8, beyond the limits 



* Gustafson : " Journ. Gen. Physiol.," 1919. 2, 217. 



