The Wohurn Pot- Culture Experiments, 1910-11-12. 323 



nature, the drought of 1911 no doubt making conditions more 

 adverse. But still, on the whole, the general conclusions of 

 former years were borne out, viz., that up to "02 per cent, zinc 

 may be present in a soil and exert a stimulating influence, but 

 that beyond this amount it is distinctly toxic. 



3. Zinc Phosphate, Zinc Nif7-ate, and Zinc Carbonate, 1912. 



It having been established that •02 per cent, of zinc in a 

 soil was about as much as could be safely used, it was decided, 

 in conjunction with the similar experiment with lithium salts, 

 to see if quantities well below this would show any beneficial 

 action. The salts determined upon were the phosphate, nitrate, 

 and carbonate, and the respective dressings were "03 per cent., 

 •02 per cent., and •Ol per cent, of metallic zinc. As regards 

 the appearing of the shoots the heavier dressings ('03 per cent, 

 zinc) of both the phosphate and the nitrate retarded the 

 germination of the seed, but eventually all the plants came up. 

 Throughout the period of growth the heavier applications ("03 

 per cent.) in no case looked so well as did the others, but the 

 smaller applications, as a rule, showed an improvement on the 

 control lots. The nitrate sets in particular had a deep green 

 colour and showed vigorous growth. It was in May, however, 

 that all the zinc-treated crops, and, in particular, the nitrate 

 ones, became attacked by a species of torula, which weakened 

 the plant very greatly. This was followed by an attack of red 

 rust, w^hich spread so much as, in the case of the nitrate lots, 

 to practically ruin the crop, for, when the excessive wet of 

 August set in, the stalks were Ijeaten down, reduced to a 

 black, rotting mass, and what corn was ultimately obtainable 

 was of little or no value for purposes of comparison. The 

 phosphate and carl)onate lots were also affected, but not nearly 

 to the same extent. At harvest they showed results in corn 

 and straw but little different from the untreated lots, so that 

 no clear evidence could be drawn froin them. The nitrate lots 

 in all cases showed great deterioration. A very interesting 

 question here arises — whether the attack on the wheat plant, 

 first by the torula and then by rust, w^as in any way connected 

 with any weakening of the plant through the action of the 

 zinc salts. This is a matter for inquiry, but it is well to state 

 here that the zinc-treated plants were alongside the lithium 

 and the lead-treated ones, and the external conditions were 

 precisely the same in all cases ; yet it Avas only on the zinc- 

 treated plants that the attack came, and this extended alike to 

 the phosphate and carbonate as well as the nitrate lots, though 

 the damage was by far the most marked in the case of the 

 last named. Plate 3 shows in {e) (/) and {g) the treatment 

 with zinc phosphate, (a) on the same plate supplying the control. 



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