Duggar — Relation of Marine Algae to Salt Solutions. 487 



phate, the other substances used are present in such small 

 quantity in sea water that they scarcely need consideration. 

 It is of interest, however, to note that although chlorides are 

 present to such a great extent in normal sea water, the addi- 

 tion of a chloride is, generally speaking, more injurious than 

 the addition of a sulphate ; yet the sulphates represent less 

 than one-tenth the concentration of the chlorides in sea 

 water, and nitrates are present only as a trace, yet they are, 

 as a rule, toxic at about the same strengths as the chlorides. 



There seems to be no easy explanation of the relative toxic 

 values of NHi, K, Na, Ca and Mg, as indicated by the results 

 given. By considering the factor of electrolytic dissociation 

 there seems to be nothing of special interest; for if we take 

 the concentrations at which the ammonium salts are toxic as 

 the points of comparison, we find that the dissociation of 

 practically all the salts used is very nearly the same. At 

 greater concentrations there would be, of course, marked dif- 

 ferences in the amount of dissociation in the various salts. 

 However, the fact remains that mere differences in the 

 degree of dissociation may not be invoked to explain these 

 relations. Otherwise magnesium chloride, which is at .0025 

 N dissociated to an extent practically equal to that of am- 

 monium chloride at the same concentration, should have 

 a health concentration at approximately .0025 rather than at 

 .24 N. 



Arber,* in a paper published since the completion of my 

 first series of experiments, reports that solutions of ammonium 

 nitrate equivalent to 1 per cent and 5 per cent potassium 

 nitrate caused the death of Ulva latissima in a fewdays. He 

 also found that the nitrates of potassium, sodium and mag- 

 nesium are inhibitory to starch formation in the order named. 

 The same author f found in earlier experiments that in the 

 absence of other salts, sodium chloride favored carbon assim- 

 ilation in this same alga, while the absence of these salts was 



• Arber, E, A. N. On the effect of Nitrates on the Carbon Assimilation ol 

 Marine Algae. Ann. Bot. 15 : 669-681. 19G1. 



t Arber, E. A.N. On the effect of Salts on the Assimilation of Carbon 

 Dioxide in Uiva latissima, L. Ann. Bot. 16 : 89-69. 1901. 



