The Woburn Pot-Culturfi. Expeyiments, 1914:. 307 



result, it fails, I think, to afford any quantitative test of the 

 extent to which the presence of a constituent may be inimical 

 or the reverse under the ordinary conditions of plant life. 

 Thus, in 1913, it was found, by growing plants in pots, that 

 considerably more than ten times as much copper as Miss 

 Brenchley had found to be harmful in the case of water- 

 culture was needed to be present in soil in order to injure 

 vegetation. 



At Woburn in 1913, wh(m using sulphate of copper, it was 

 found that •05 per cent, of copper in the soil or anything more 

 than this, prevented a crop from growing, or else very 

 materially reduced it ; *02 per cent or less than this exercised, 

 however, no injurious effect or even had a stimulating one ; 

 while, when carbonate of copper was used, "1 per cent, of 

 copper or more showed injury, and 'Oo per cent, or lesser 

 quantities had a stimulating effect. It was thought desirable 

 to repeat this experiment and to use other salts of copper as 

 well. Accordingly, the experiments of 1914 took the form of 

 using copper as sulphate, phosphate, carbonate, nitrate and 

 arsenite respectively, the amounts of copper in each set being 

 •10, •Oo, •02. •Ol, and ^005 per cent, respectively. 



The experiments were carried out on wheat in earthenware 

 pots holding 40 lb. of soil each, and each experiment was in 

 duplicate. The salts were intimately mixed with the whole of 

 the soil held in each pot. 



The soil used in these experiments was from Butt Furlong, 

 and was a much richer soil than that used in the experiments 

 of 1913. This is shown by a comparison of the untreated 

 produce of the two years, the actual weights obtained for a 

 single pot being as follows : — 



Actual weight of untreatecJ produce 



1913 



1914 



Corn 



Grms. 

 1116 



Straw 



Corn 



Straw 



Grms. j Grms. 

 16-63 I 34-60 



Grms. 

 73-48 



In consequence of the better soil, the produce all round 

 was much larger than in 1913. This same fact may account 

 for the effects of the copper salts — though tending in the same 

 direction as in 1913 — to have not been so marked as then. 



The pots were filled with soil towards the end of 

 November, 1913, and wheat ("Red Standard") was sown on 

 December 1, twelve grains per pot. Germination was some- 

 what irregular, but the main points to remark upon are that 

 the only salts to seriously affect germination were the heaviest 



