38 CELLULAR 



the same conclusion is reached as the result of 

 studies on the penetration of carbon dioxide. 



It is true that, as far as final concentrations 

 are concerned, we might expect a similar result 



Fig. I demonstrates that the total sulphide in the sap corre- 

 sponds with the undissociated HgS in the external solution. 

 Ordinates represent undissociated H2S in the case of sea water 

 and total sulphide (HgS + HS' + S") in the case of sap. 

 Abscissae represent pH values. The concentration of total 

 sulphide (H2S + HS' + S") in the cell sap (O) is expressed 

 as per cent of the total sulphide in the outside solution. The 

 values for the concentration of undissociated HgS in the sea 

 water as calculated from the dissociation constant (D) and 

 as determined from the vapor tension (A) and from the rate 

 of evaporation (X) at various pH values of the external 

 solution are expressed as per cent of the corresponding values 

 in the range pH i to 3 where all the HgS is regarded as 

 undissociated. Each point represents one determination. 



