ACTION OF SALTS 133 



with continued absorption of water, there is an acceleration 

 in the respiration until a water content of 200 per cent, is 

 reached, after which the respiration rate is slower. The alga 

 constituent of Parmelia physodes is a species of Trebouxia 

 which Fraymouth found to be less capable of responding to 

 drought conditions than the free growing Trebouxia which 

 showed a maximum rate of respiration when the water content 

 was about 30 per cent. The alga Prasiola crispa behaved 

 similarly ; as in Trebouxia, after severe and prolonged drought, 

 the respiration is so feeble as to be hardly determinable, but 

 immediately on the access of water the respiration rate rises 

 to a value equal to that of the fresh plant with an equivalent 

 water content. Comparable results were obtained with the 

 moss Hypnum. 



SALTS. 



The action of salts on the intensity of respiration varies 

 according to their chemical nature, their concentration and 

 their association with other salts ; thus salts of the heavy 

 metals are very toxic whilst those of the alkali metals and 

 alkaline earths accelerate or retard according to their con- 

 centration and association. Lyon * found that phosphate 

 accelerates both the aerobic and anaerobic respiration of 

 Elodea. Nitrosomonas shows a maximum respiration in N/200 

 ammonia, whilst a strength of N/10 depresses respiration in a 

 marked degree. f Similarly the respiration of Bacillus sub- 

 tilis is constant in the presence of low concentrations of the 

 chlorides of sodium, potassium and calcium ; an increase in 

 concentration leads to a reduction in respiration. Compared 

 with cultures lacking these salts, the respiration intensity 

 is increased by the presence of sodium chloride, potassium 

 chloride, calcium chloride or magnesium chloride in concen- 

 trations of -2M, -I5M, -05M, and -03M respectively. In 

 higher concentrations the rate of respiration is decreased.^ 

 With regard to concentration, Inman § studied the behaviour 

 of Laminaria and Chlorella. 



* Lyon : " Journ. Gen. Physiol.," 1924, 6, 299. 



f Meyerhof : " Pfluger's Archiv," 1917, 166, 240. 



t Brooks : " Journ. Gen. Physiol," 1919, 2, 5 ; 1920, 2, 331. 



§ Inman : id., 1921, 3, 533 ; 4» I 7 I - 



