208 THE CANADIAN NATURALIST. [June, 



contain in their ash, at th(^ above-stated proportion of 0*1 percent., 

 just 53*76 lbs. of phosphoric acid ; a result in curio islj-close corres- 

 pondence with the quantity of phosphoric acid contained in the 

 superphosphate used. The mean yield of the two plots manured 

 with fivecwt. of superphosphate each did not differ from the yield of 

 the plot manured with only three cwt. so much as the respective pro- 

 ducts of those two plots differed from each other. Hence it appears 

 that the addition to the soil of a larger proportion of soluble phos- 

 phoric acid than the turnip-plants could consume had no " specific" 

 influence in promoting their growth in this case. As for the crop 

 of the plot manured with seven cwt. of superphosphate, it not only 

 did not exceed, but fell short by a few cwt. of the mean yield of the 

 plots manured with five cwt. each. A still further deficit, of a few 

 cwts., was observed in the yield of the plot manured with ten cwt. 

 of superphosphate. Both these deficiencies, however, were less than 

 the difference of yield by the two plots equally manured. So that 

 in this case, the yield of the plot which received in the manure 

 the exact quantity of phosphoric acid removed in the crop was 

 (within the limits of experimental error) equal to the yield of 

 plots, respectively supplied with quantities 66 per cent, 133 per 

 cent, and 233 per cent greater. Two plots which werp left 

 unmanured, on this occasion, for comparison's sake, gave a mean 

 yield of only 330 cwt. of turnips per acre : being about one third 

 less than the yield of the manured plots. 



Hence it would appear that the turnip-plant benefits ^>y an arti" 

 ficial supply of soluble superphosphate up to, but not beyond, the 

 limit of its assimilating powers. And if it be admitted that the 

 phosphates of the soil are in a less soluble state than the artificial 

 Superphosphate (a probable supposition), this case would seem to 

 argue that the roots, of the turnip, when simultaneously presented 

 with different forms of phosphatic food soluble in different degrees? 

 prefer the most soluble, and imbibe this first. 



These results, in the reporter's judgment, stand in strong oppo- 

 sition to those obtained at Rotbamstead, and tend to negative the 

 yiew that phosphoric acid benefits turnips by some " specific 

 agency," other than that due to it as a constituent of their ash. 



The advocates of the '* specific " doctrine, however, take up 

 another ground. It is, they say, a universally recognized fact 

 among farmers, that, in the ordinary course of husbandry, super 

 phosphate— not potash — ^is the manure for turnips, though potash 



