112 



A. P. MATHEWS 



cally be, so far as he has tried those of which the solution tension is 

 known. The same exceptions are also apparent. Thus cobalt is 

 not sufficiently toxic, and zinc is too toxic for the rule. Lead is about 

 where it belongs, but in this case barium is the marked and peculiar 



- 1 



- 2 



1 MG 2 MN CD 3 4 Ac 



X= Ionic Potentials. 

 FIG. 5. Plot of results obtained with Volvox. Abscissae and ordinates as in Fig. 3. 



exception, in place of the lead toward diastase, and cadmium toward 

 the Fundulus egg. 



The results of Heald (Table i) so far they have been obtained 

 with the salts we are examining, show much the same order of effi- 

 ciency. Thus for Pisum sativum the order of toxicity is : Ag, Hg, 

 Cu, Ni, Co, and H; while for Zea mais it is Ag, Cu, Hg, Ni, Co, 

 and H. These results are not of a sufficiently definite character, 

 based as they are on the growth of roots, to enable very accurate quan- 



