452 Dandeno — Relation of Mass Action to Toxicity. 



the food of plants in greater proportion than occurs in the 

 aqueous extract of ordinary soil." This is probably the reverse 

 of the actual condition, because, as has already been pointed 

 out, the soil particles have a physical attraction to be satisfied. 



The question of selective power of plants is a vague one. 

 It is probably more a name than a fact. The soil selects as 

 well as the plant. 



So far as this physiological problem is concerned, it seems 

 that the theory of electrolytic dissociation is insufficient. Cer- 

 tainly no support to the theory comes from the physiological 

 side. Acetic acid, sodic carbonate, sodic bicarbonate and car- 

 bonic acid exhibit phenomena quite in opposition to it. Con- 

 clusions have been published which, from the data, seem to be 

 entirely unwarranted. Cameron virtually points this out, say- 

 ing : " The necessity of such assumption would seem to abso- 

 lutely invalidate the use of such organisms and criteria for the 

 testing of the dissociation hypothesis in any quantitative way." 

 On the other hand, in Jones' ' Theory of Electrical Dissociation,' 

 p. 272, is stated : " The theory of electrolytic dissociation has 

 thus thrown light upon the physiological action of different 

 substances, and the theory has itself been strengthened by 

 these experiments upon living things." Kow the experiments 

 recorded in this paper show that the theory throws no light 

 upon such physiological problems, rather the reverse, if any- 

 thing. A further quotation will show that Jones did not 

 examine the matter as carefully as might be expected, in con- 

 sideration of the fact that he was compiling a text-book. He 

 states, p. 271, referring to the work done by Heald : The Cu 

 ion is about as toxic as the hydrogen ion," and on page 270 : 

 " In the case of strong acids the root would just live in a solu- 

 tion which contained a gram molecular weight of the acid in 

 6400 liters," and further on : " The roots would just survive in 

 a solution which contained a gram molecular w T eight of copper 

 ions in 51200 liters." It should be remembered that these 

 quotations from Jones are taken from a recent text-book. A 

 glance at them will convince one that little, if any, care has 

 been taken to present the matter accurately. This is a misin- 

 terpretation of Heald for which Heald is in no way responsible. 



In the first place, there is no evidence from the physiolog- 

 ical side for the theory of electrolytic dissociation, and in the 

 second place, references have been made over and over again 

 to the earlier investigations, with no sure foundation. When 

 these creep into text-books, it is supposed they are considered 

 to be established facts, and, therefore, all the more need to call 

 attention to them. 



An illustration may show the mistaken notion following the 

 application of the theory of dissociation to explain certain 



