Physiological Observations 193 



that considerable labor was required to keep the ditches clean. 

 These mosses have now entirely disappeared from the upper 

 canals, due in part to the turbid waters in which they will not 

 grow, and in part, perhaps, to the dissolved copper from the 

 mines. 



PHYSIOLOGICAL OBSERVATIONS ON TOXIC EFFECTS 



OF COPPER SALTS 



Quantitative Work 



Citrus seedlings placed in copper sulphate solutions contain- 

 ing from 2.5 to 100 parts of copper in 1,000,000 of distilled 

 water wilted in forty-eight hours, thus showing effects of toxicity. 

 Root tips then all turned red with K^FeCyg. Red root-tips 

 sectioned showed under low power red cells under bark and 

 around center. Citrus, cucumber and bitter melilot roots 

 grown in 10:1,000,000 copper solution all gave violet reaction 

 with KOH, less delicate but more distinctive than K^FeCy^, since 

 the purple biuret test indicates both copper and protein. 



Cultures of wheat, peas, corn, beans, and other. plants grown 

 in soils- containing from 0.005 to 0.1 per cent of copper in soil, 

 gave only very doubtful root-tip reactions with K^FeCye, 

 although showing evident injury, especially in 0.1 per cent cul- 

 ture. There is an essential difference between water-culture 

 roots placed in copper solutions and roots grown in soil. The 

 first are killed by excess of copper salts contained ; the second 

 are yet living and growing resistantly in the soil. 



A 0.1 per cent copper culture of corn, wheat, beans and 

 cucumbers was washed out from the soil and gave superficial red 

 coloration with K^FeCyc, but' not internal. Living tissue is 

 evidently inconsistent with sufficient amounts of copper to give 

 a plain internal test. Therefore, the small amounts of copper 

 known to be in poisoned but living root systems must be dissem- 

 inated. It is, therefore, of interest to know the copper-protein 

 ratio in poisoned but living root systems, such a ratio being more 

 significant than the ratio of copper to the whole mass of root 

 systems, which includes various proximate principles not con- 

 cerned, in copper fixation. 



