18 GROWTH OF WHEAT SEEDLINGS. 



phenomenon has been often noted in the limestone regions, particu- 

 larly in the Shenandoah Valley of Virginia, where soils derived from 

 limestone rocks, and evon now having the undecomposed limestone 

 within a few feet of the surface, have become so acid that clover 

 can no longer be advantageously grown. Ground limestone applied 

 to the surface soil will often restore its original fertility. 



The heavy clay soils from which bricks are made are always acid, 

 have a high lime requirement, and are usually very unproductive. 

 The oxids of iron exist in such soils in a finely divided colloidal form 

 brought about by an acid condition, and they are usually remedied 

 by an application of lime. The poisonous properties of subsoils also 

 may be due in a large measure to their acid character. 



Investigators working with solution cultures and using single 

 salts might do well to take into consideration the reaction of the 

 solutions after the plants have been placed in them. The moment 

 seedlings are placed in a solution of potassium sulphate a rapid 

 absorption of potash begins with a consequent formation of sulphuric 

 acid. This sulphuric acid is a disturbing factor and other sub- 

 stances placed in the solution and kept under observation might 

 owe their apparent beneficial effect to the fact that they simply act 

 as bases, but in themselves have no direct influence upon the plant. 

 In field culture the residual injurious effect of an application of 

 sulphate and chlorid of potash can be overcome by mixing the 

 fertilizer with about twice its weight of lime. 



In the experiments here recorded it is shown that the seedlings 

 grown in culture solutions containing potassium chlorid, potassium 

 sulphate, or hydrochloric or sulphuric acid solutions (10 parts per 

 million), exert a selective action whereby the potash ion is absorbed 

 by the roots, while the chlorid or sulphate ion is for the most part 

 left in solution. This causes the solution to become acid, which in 

 turn acts injuriously on the root development. 



The addition of lime or iron or aluminum hydrate to culture 

 mediums containing potassium chlorid, potassium sulphate, hydro- 

 chloric acid, or sulphuric acid, keeps these solutions alkaline so that 

 they then act favorably on the root development. This would tend 

 'to explain why field applications of sulphate or muriate of potash in 

 time render the soil acid, 1 and why the continued use of Chile salt- 

 peter produces an alkaline condition of the soil. 



1 At the Woburn Experiment Station it has been amply shown that a continuous ap- 

 plication of ammonium sulphate renders the soil so acid as to cause the crop to be almost 

 an absolute failure. Adjacent plats, likewise treated with ammonium sulphate, but also 

 given an application of lime, have continued to yield crops as large as are produced by 

 still other plats treated with sodium nitrate only. 



O 



