The Woburn Pot- Culture Experiments, 1914. 311 



illustrate also in comparative form the effect of the same amount 

 of copper, but used in different salts. This is accordingly 

 illustrated by Plates 5-12. These are set out for the following 

 respective amounts of copper : — 'lO per cent. (Plates 5 and 6), 

 •05 per cent. (Plates 7 and 8), "02 per cent. (Plates 9 and 10), 

 and -01 per cent. (Plates 11 and 12). The first Plate of each set 

 gives the growing crop, the second the corresponding roots. It 

 will be seen from these how marked is the difference, alike in 

 crops and in roots, between the effect of one and the same 

 amount of copper when applied in different forms. 



Taking, first, the highest amount ("10 per cent.) of copper, 

 Plate 5 shows marked deterioration of crop with sulphate of 

 copper, an increased crop with the phosphate, a diminished one 

 with the carbonate (though not to the same extent as with the 

 sulphate), and almost no crop at all with the nitrate, while with 

 arsenite of copper germination was entirely destroyed. As 

 regards the roots, Plate 6 shows these to be feathery and 

 smaller than the untreated in the case of the sulphate and 

 carbonate, while they are of normal nature and well developed 

 Avith the phosphate. With nitrate there was almost no root 

 growth. 



Passing to •05 per cent, of copper, Plate 7 shows the crop 

 with sulphate of copper to be slightly below the untreated, to 

 be increased with the phosphate, to be about normal with the 

 carbonate, and to be greatly reduced with the nitrate. The 

 corresponding roots (Plate 8) were large and feathery with the 

 sulphate and carbonate, feathery, but small, with the nitrate, 

 but quite normal with the phosphate. 



With '02 per cent, of copper (Plate 9) the crop with sulphate 

 of copper was better than the untreated, this being also the case 

 with the phosphate and the carbonate, the latter showing a 

 shorter but thicker and heavier crop. With the nitrate the 

 straw was not so long, but the crop proved to be equal in 

 weight to the untreated. With the arsenite a few stalks only 

 were seen, but no grain was produced. The corresponding 

 roots (Plate 10) were large and feathery with the carbonate and 

 nitrate, but normal with the sulphate and phosphate. 



Lastly, with '01 per cent. (Plate 11), the sulphate, phosphate, 

 and carbonate all showed increase of crop ; the nitrate gave a 

 shorter but thicker crop and an increased weight, while the 

 arsenite yielded about a half-crop. The corresponding roots 

 (Plate 12) showed a tendency to featheriness in the case of the 

 nitrate only, the remainder being quite normal. 



It is clear, therefore, that the same amoujit of copper acts 

 very differently according to the form in which it is supplied. 



