into the subsoil. Aside from the impoverishment in basic nutritive sub- 

 stances the copper sulfate (such plants as grasses, for instance, take up 

 rather considerable amounts of copper and zinc salts) acts finally also as a 

 direct poison so far as cultural experiments in nutrient solutions^ have 

 demonstrated. 



Masayasu Kanda- found that, in water cultures of peas, injuries 

 appeared even with 0.000000249 per cent, of copper sulfate. On the other 

 hand, if added to soil in a concentration a million times greater, it acted as 

 a stimulant. The conditions are even more favorable for plants in natural 

 soil. According to Tschirch^ almost all plants possess some copper since, 

 indeed, all field soils may contain traces of it. The vegetation, on soils to 

 which copper is added abundantly, takes up usually but very little copper, 

 50 that the danger of poisoning is not imminent. This theory finds sub- 

 stantiation also in the fact that in the very frequent use of copper sulfate as a 

 spraying substance against parasitic diseases a constant enrichment of the 

 soil takes place without any injuries being demonstrable with certainty. We 

 personally believe, at any rate, that a time will come in which a constant 

 addition of copper will make itself felt as a retardation to vegetation. 



The waste water containing nickel and cobalt found near nickel-rolling 

 factories will act in the same way as described above. It may be mentioned 

 here supplementarily that John^ in 1819, in his book "The Feeding of 

 Plants," had studied sand and water cultures to which solutions of different 

 metallic salts had been added. He proved thereby that sunflowers did not 

 take up copper given them in the form of insoluble copper carbonate, while 

 peas and barley stored up great masses from a soil to which a solution of 

 copper nitrate had been added drop by drop. 



The fact that local conditions sometimes make possible a beneficial use 

 of the waste water but at other times cause injurious factors to be felt, 

 prevents our consideration in more detail of the different industries. In 

 this connection the poisonous peculiarity of the soil, due to its power of 

 absorption, plays a principal part. Hattori' calls especial attention to this 

 in regard to copper salts. 



The injuries due to municipal irrigation with liquid sewage have been 

 mentioned already in the section "Sewage Disposal Fields" (page 364). 



1 otto, R., Untersuchungen liber das Verhalten der Pflanzenwurzeln gegen 

 Kupfersalzlosungen. Zeitsclir. f. Pflanzenkrankh. 1S93, p. 322. 



2 Masayasu Kanda, Journ. College of Science. Tokyo, "Vol. XIX, Art. 13. 



3 Tsehirch, A., Das Kupfer voni Standpunkt der gerichtlichen Cheniie, Toxi- 

 kologie und Hyg-iene. Stuttgart 1893, Fr. Enke, 8°. 138 p. 



•1 Miiller, Carl, Zur Geschichte der Physiologic und der Kupferfrage. Zeitschrift 

 flir Pflanzenkrankh. 1894, p. 142. 



5 Just's bot. Jahresber. 1902, Absch. Krankh. Ref. 277. 



