324 The Wohurn Pot-Cnlture Experiments, 1910-11-12. 



Plate 6 shows in {a) (h) and (c) the action of zinc nitrate (the 

 control being (a); of Plate 5), and Plate 8 shows in (a) (h) and 

 (c)'the action of zinc carbonate, the control being given in 

 (a) of Plate 7. 



It is clear from this experiment of 1912 that a fresh factor 

 — that cf the existence of fungoid disease — comes in, and calls 

 for investigation in the futnre. Whether there be any con- 

 nection between the occurrence of this and the presence of the 

 zinc salts requires to be ascertained. Meantime, however, one 

 cannot go beyond -the general conclusions so far found, viz., 

 that zinc salts if containing above '02 per cent, of that metal 

 will exercise a toxic influence, but below that figure will have 

 a slightly stimulating effect, this being the most marked with 

 the more soluble salts, and, in pai-ticular, the nitrate. 



It is worthy of note that these figures found for zinc are no 

 less than ten times as much as those found for lithium. In 

 other words, lithium exercises quite ten times the toxic or the 

 stimulating influence that zinc does. 



(c) T?ie infiuence of Lead Salts on Wheat, 1912. 



In 1912, when experiments were being conducted with 

 lithium and zinc, it was decided to try lead in similar forms of 

 combination. Accordingly an experiment was arranged, in 

 which lead phosphate, lead nitrate, and lead carbonate were 

 respectively used, the amounts of lead (metal) contained being 

 •03 per cent, "02 per cent, and '01 per cent. Used in these 

 amounts lead was found to be a particularly inert material, so 

 far as the phosphate and the carbonate were concerned, for 

 these salts seemed to exercise no influence on the incubatiiui of 

 the seed, nor to possess either toxic or stimulating properties. 

 The harvest results were practically tlie same as with the 

 control (untreated) set. The lead nitrate, however, showed 

 distinct stimulating influence, and at harvest the comparative 

 results were : — 



Corn Straw 



Untreated 100 100 



Lead nitrate, "U;^ per cent, lead . . 162 15S 



„ -02 153 134 



„ 01 13n 127 



Plate 6 shows, in {d), (e) and (/) the action of lead nitrate, the 

 "control" being given in {a) of Plate 5 ; and Plate <S gives, in 

 (d), (e) and (./') the action of lead carbonate, the "control" 

 being («) of Plate 7. It will be noticed that lead nitrate and 

 lead carbonate did not exert the injurious influence that the 

 corresponding zinc salts did. Nor was there any failure with 

 the lead phosphate such as occurred with the heavier dressing 

 (•003) of lithium phosphate. 



