22 Effect of Copper Compounds 



control. This was apparently due to the action of the unneutralised 

 copper. The indications are that the conspicuously effective part of 

 the molecule is the cation or metal, and that the anion plays little or 

 no part in causing the toxicity ; in such great dilutions the metals act 

 as free ions. The hypothesis is put forward that interior physiological 

 modifications are responsible for the observed differences in growth rate, 

 the cell processes being so affected as to bring about different results on 

 cellular growth ; in other words, the growth rate represents the physio- 

 logical sum of oppositely acting stimuli or of antagonistic protoplasmic 

 changes where mixtures of salts occur. This is really an extension of 

 Heald's idea that the toxic effect of a poison is due partly to changes in 

 the turgescence of the cell, a sudden decrease causing retardation or 

 inhibition of growth, and partly to a direct action on the protoplasm, 

 which differs in different plants with the same salt. Heald (1896) 

 went so far as to suggest that the poisonous action is a mere matter 

 of adaptation and adjustment, since toxic substances are not usually 

 present in soil, but this assertion is too sweeping to be accepted in its 

 entirety, although it probably holds good to a certain extent with some 

 species of plants. 



Kahlenberg and True (1896) found that the addition of an organic 

 substance produced the same effect as the addition of some nutrient 

 salt, in that it reduced the toxicity of the copper salt, e.g. in the 

 presence of sugar and potassium hydrate the lupins were able to with- 

 stand a concentration of 1/400 copper sulphate, part of which reduction 

 of toxicity is attributed to the sugar. 



(c) Effect of adding insoluble substances to solutions of copper salts. 



Other investigators have shown that the presence of insoluble 

 substances has a similar effect in reducing toxicity to an even greater 

 degree. True and Oglevee (1904, 1905) again used Lupinus albus as 

 a test plant in the presence of solutions of various poisons in pure 

 distilled water, copper sulphate, silver nitrate, mercuric chloride, hydro- 

 chloric acid, sodium hydroxide, thymol and resorcinol all coming under 

 consideration. Clean sea sand, powdered Bohemian glass, shredded 

 filter paper, finely divided paraffin wax and pure unruptured starch 

 grains were respectively added to the solutions, and seedlings were 

 suspended over glass rods so that their roots were in the solutions for 

 24 48 hours. The solids varied in their action on the different poisons ; 

 while the toxic influence of mercuric chloride was reduced by sand 

 and crushed glass, the action of silver nitrate was modified by nearly 



