41 



pletely at a given concentration according to the specific properties of 

 the x^articnlar salt. The result is a liberation of ions — atoms or atomic 

 groups carrying or in some way associated with an electric charge. 

 Cathions, those furnished b}' the basic radicle, carry positive elec- 

 tricity, while anions, derived from the acid radicle of the salt, are 

 negatively charged. Ions possess a much greater velocity ^ than do 

 undissociated molecules, and it is now believed by many physiologists 

 that salts owe to the properties of their ions rather than to their entire 

 molecules the toxic and other action which they exert upon organisms.^ 



It is believed that the results of the present investigation tend to 

 confirm this view, althougli it must be admitted that serious anomalies 

 exist, to some of Avhich attention has already been directed. 



Pure solutions of the salts dealt with are shown to be generally 

 injurious to plants, and this largely l)y virtue of the cathions which 

 the}' yield, as a comparison of the position of the several salts in the 

 table of toxicity in pure solutions shows conclusively. Thus magne- 

 sium salts, irrespective of the character of their anions, are much 

 more injurious than is any sodium salt, while the three chlorides (of 

 magnesium, sodium, and calcium) differ enormously in toxicity, 

 regardless of the fact that they yield a common anion. 



An inspection of the tables of limits in mixed solution given above 

 makes it clear that the addition of a second, less toxic salt in most 

 cases increases the concentration of solution of the more harmful one 

 in which root tips can retain their vitality. It is also demonstrated 

 that addition of a second sal: of the same base, hence furnishing a 

 different kind of anion only, is usually' much less efficacious in raising 

 the limit than is the admixture of a salt of a different base. Thus 

 magnesium chloride is ineffective as an antidote to magnesium sul- 

 phate, sodium chloride to sodium carbonate or to sodium sulphate, 

 and calcium carbonate to calcium chloride. 



If the assumption be granted that in the dilutions here involved 

 the magnesium salts are practically completeh^ dissociated and that 

 the anions do not have a toxic effect, then a 0.00125 normal solution 

 of magnesium will be the limit when the metal is combined as the sul- 

 phate and a 0.0025 normal solution when combined as the chloride, but 

 about a 0.002 normal solution when both chloride and suli^hate are pres- 

 ent, with two equivalents of the former to one of the latter. The same 

 line of reasoning holds for the other cases cited, and from these facts it 

 is evident that the anions have a part in determining the toxic effect of a 



' That the physiological action of ions may be in some sort a function of their 



specific velocities is indicated by Loeb's comparison of the effects of hydrogen and 

 hydroxyl ions, as well as of various basic cathions, upon the absorption of water 

 by a muscle. [Pfliiger's Archiv.. 69, 21. (1898).] 



- Of a rapidly growing literature on this subject the papers of Kahlenberg and 

 True and of Kahlenberg and Austin, dealing with plants, and those of Loeb, 

 Garrey. Anne Moore, Kahlenberg. Clark and others, treating ion action upon ani- 

 mals, may be cited as of great importance. (See the Bibliography, p. 56.) 



