18 Effect of Copper Compounds 



cow pea the first three of these being the species used by Otto- 

 were grown in (1) ordinary distilled water, which was found to contain 

 traces of copper, (2) glass distilled water, for about a month, till no 

 more growth was possible owing to the lack of nutriment. In every 

 single case the root growth was checked in some degree in the ordinary 

 distilled water, the roots seeming to the eye to be less healthy and less 

 well developed. In Pisum, Tropeolum and Zea, the shoot growth of the 

 coppered plants appeared stronger than that of the controls, and this 

 was borne out when the dry weights of the plants were obtained. In 

 every other case the coppered plants were inferior, root and shoot, to 

 those grown in the pure water. With the first three plants it appears 

 that while the toxic water has a bad effect on the roots, yet the growth 

 of the shoots is increased. The idea suggests itself that this apparent 

 stimulation is in reality the result of a desperate struggle against 

 adverse circumstances. The roots are the first to respond to the action 

 of the poison, as they are in actual contact ; their growth is checked, 

 and hence the water absorption is decreased. No food is available in the 

 water supply from the roots, so the plant is entirely dependent on the 

 stores laid up in the seed and on the carbon it can derive from the air 

 by photo-synthesis carried on by the green leaves. The result of the 

 root checking in these particular cases seems to be so to stimulate the 

 shoots by some physiological action or other, that this process of photo- 

 synthesis is hastened, more carbon being converted into carbo-hydrates, 

 so that the shoot development is increased, yielding a greater weight 

 of dry matter. In each of the other cases observed the shoot was 

 obviously not stimulated to increased energy by the poison, and so the 

 whole plant fell below the normal. 



Other experiments showed that barley roots are peculiarly sensitive 

 to the presence of minute traces of copper, as very little root growth 

 took place in the copper distilled water, and root growth was also 

 entirely checked by the presence of one part per million copper 

 sulphate in the pure glass distilled water. Yet again, one litre of pure 

 distilled water was allowed to stand on a small piece of pure metallic 

 copper foil (about 1^-" x J") for an hour, and even such water exercised 

 a very considerable retarding influence upon the root-growth, checking 

 it entirely in some instances. 



Some years before True and Gies published their results, Coupin 

 (1898) had grown wheat seedlings in culture solutions with the addition 

 of copper salts for several days in order to find the fatal concentrations 

 of the different compounds. Taking toxic equivalent as meaning " the 



