302 



PERMEABILITY IN PLANTS 



the different plants. Thus it was found that in the case of Rhody- 

 menia it required more Ca to antagonize Na than it did in the case 

 of Laminaria. It was also observed that in the case of Rhodymenia 

 (Fig. 2) the antagonism was not so great as in Laminaria and this 

 appears to be correlated with the fact that less decrease of permea- 

 bility is produced by Ca in Rhodymenia (Fig. 1). In other words, the 

 effect of such a substance as Ca upon permeability not only indicates 



Per cent 



140- 



lOCMb 



60- 

 Mrs. 



Fig. 1. Curves showing the effect of CaCl2 0.278 m on the electrical resist- 

 ance of Laminaria (upper curve) and of Rhodymenia (lower curve). The ordi- 

 nates denote net electrical resistance expressed as per cent of the normal re- 

 sistance in sea water (which is taken as 100 per cent). Temperature 17° =*= 2°C. 

 Average of six experiments. Probable error less than 3 per cent of the mean. 



what substances it will antagonize, but also, to some degree at least, 

 the amount of antagonism. 



It may be added that Rhodymenia affords an interesting confirma- 

 tion of the value of the electrical method in measuring antagonism 

 since the plants begin to change color soon after injury occurs. It was 

 found that the relative rates of death as indicated by color changes 

 in NaCl, CaCl2, and the various mixtures corresponded with the re- 

 sults obtained by determining conductivity. 



