MANURING AND FERTILIZING 33 



4. Increase the quantity of water transpired per gram 

 of dry matter. 



Hecke 1 shows that the application of potassic fertil- 

 izers has a marked influence in the production of 

 tubers and roots, and that potash assists in the forma- 

 tion of starch. Lawes and Gilbert 2 noted that the 

 percentage of potash was relatively high when the 

 supply of it was relatively liberal and vice versa, but 

 the variations are small, and that where there was a 

 deficiency of potash in the supply and in the ash there 

 was generally an increased supply of lime in the ash. 



Which is the Better Source of Potash, Sul- 

 phate or Muriate of Potash ? This question is 

 still unsettled, because, apart from other considerations, 

 one of the deciding factors is the relative cost of each. 

 In many cases the results are inconclusive, 3 while in 

 some cases 4 the fertilizers appear to be of equal value. 

 In others 5 sulphate of potash gave better results; thus 

 Davidson, of Virginia/ found that the potatoes grown 

 by sulphate of potash contained more dry matter but 

 a less percentage of starch than those fertilized with 

 muriate of potash. Brooks 7 found that sulphate of 

 potash gave a greater yield per acre of merchantable 

 tubers, which were of larger size and of superior eat- 

 ing quality, containing 2 to 3 per cent, more starch, 

 and, when cooked, the potatoes were whiter, of better 

 flavor, audr more mealy. 



1 E. S. R., VII., p. 667. 2 Rothamsted Memoirs, Vol. VI., "Experi- 

 ments on the Growth of Potatoes." 3 (N.Y.) Geneva Bui. 137, pp. 604, 620. 

 * N. H. Bui. 41, p. 13. 8 Mass. (Hatch) Report, 1896, p. 22 ; R. I. Bui. 65, 

 p. 133 ; Mich. Bui. 131, p. 10; (N. Y.) Geneva, Bui. 137, pp. 621, 622. 6 Va. Bui. 

 92, pp. 107, 108. 7 Mass. (Hatch) Report, 1904, p. 122. 



