RESPIRATION 301 



Concentration of medium C0 2 produced -per 



in -per cent hour in mg. 



154.0 ' 



15 122.7 

 25 79.4 



50 69.7 



Changing the osmotic pressure may have less effect upon the 

 respiration of marine algae, which live in a medium of high osmotic 

 pressure, than upon that of land plants. Thus the respiration of 

 Fucus vesiculosus, which lives between tides and is used to great 

 changes in the osmotic pressure of the environment, is affected 

 very little by changes in osmotic pressure; the respiration of 

 F. serratus, which lives in deeper water, is much more sensitive 

 to changes in the osmotic pressure of the surrounding water. 



In regard to the respiratory quotient, Purievich (1900) obtained 

 with Aspergillus a quotient of about one with a 10% sucrose 

 solution, while on increasing or decreasing the concentration the 

 quotient diminished. 



Water. — The influence of the concentration on respiration is 

 directly connected with the effect of water. As might be expected, 

 an increase of water results in an increase of respiration up to a 

 certain optimum. As plants dry out, respiration decreases, with 

 the result that in resting seeds with very little water content, 

 respiration proceeds at a very slow rate. Not all plants have the 

 same water optimum but all are influenced by the amount of 

 water present. The explanation of this is not agreed upon because 

 of the many parts which water plays in plant activities. All 

 processes require an optimum degree of turgor in the cell; and 

 for the formation of the enzymes, as well as for the oxidative 

 process itself, a certain minimum of water is necessary. 



Salts, etc. — The action of the various mineral salts on the in- 

 tensity of respiration varies with the nature of the salt, the con- 

 centration, and the other salts present. From what has been 

 said in previous chapters on the effect of concentration and on 

 the balancing function of salts (Chap. XI) this is not surprising. 

 Also a high concentration of salt will tend to lower the supply of 

 available water (Chap. XIX), and part of the salt effect is due to 

 this, but there are many specific effects in addition. For example, 

 phosphates first decrease and then accelerate the respiration of 

 Elodea (Lyon, 1924), and nitrogen compounds, especially amino 

 acids, decidedly increase respiration. 



