No. 6. DEPARTMENT OF AGRICULTURE. 193 



appearing in the Donegal soil, showed no gain from phosphoric 

 applications, until after .several years' continuous cropping with 

 tobacco had depleted the more available amounts. We may, there- 

 fore, regard results obtained by the Uyer method as valuably sug- 

 gestive, but not conclusive, with respect to a present deliciency in 

 potash and phosphoric acid. 



There is much study at the present lime of the relations between 

 soil fertility and the solubility of the various soil constituents in 

 water, as shown by newly devised methods supposed to be very deli- 

 cate. Scientific proof of the sufficiency of the methods of analysis 

 IS not jet adduced, and, inasmuch as the results offered in evi- 

 dence are conflicting, and represent few samples of Pennsylvania 

 soils, they will receive no extended consideration at this time. Men- 

 tion of the method suggests a statement, however, of the present 

 theories concerning the manner in which plants take up their soil 

 foods, and the«material.s that supply them. Plants have no .mouths 

 hj which their roots may devour food. The tender skins of the young 

 roots and root hairs are much like the walls of the animal stomach 

 and intestines, and drink up the substances already dissolved in the 

 soil moisture, or else, by means of the organic acids contained in 

 their cells, or by aid of the carbonic gas they excrete, attack the 

 solids with which they lie in close contact, and take from them food 

 substances, much as the strawberry absorbs sugar with which it is 

 covered. There is one school of plant physiologists and soil inves- 

 tigators who hold that the quantity of food absorbed directly from 

 the soil particles is not considerable, as compared with the quan- 

 tities obtained through the general solvent action of the soli 

 moisture. From all the facts I have at command, it is my judgment 

 that direct action by the roots, which has been repeatedly proven 

 to occur, is one of the food-consuming activities of the plant too 

 important to be left out of consideration in any theorv of soil fer- 

 tility. 



I have- said nothing concerning the humus and nitrogen of the 

 soils. The rolntinn of linmus to soil fortuity is nuo of prime impor- 

 tance, but the limits of timo prohibit its ade(jUHte discussion at this 

 time. T will simply say in passing that the decaying organic mat- 

 ters in the soil enter into coTnbination with part of the mineral mat- 

 ters. Snyder and Ladd have found that the yield of wheat by the 

 prairie loams of Minnesota and North Dakota has a close relation 

 to tlie amounts of phosp.horic acid and nitrogen in the more soluble 

 part of the humus. Similar relations are not, however, of general 

 occurrence. 



From the consideration of what I have already said, you will, 1 

 trust, have gained a fair notion of both the values and the limita- 

 tions of soil analysis by the present methods, and, from a comparison 

 of the results obtained in the analysis of limestone soils, and of 

 the Penn sandy loam series, will have come to judge how far analyses 

 from a single locality on a formation may afford indications of value 

 with respect to the formation at large, es])ecially if the topography 

 be considered. You will also understand why the station declines 

 to spend from |10 or flOO on a complete analysis of a spoonful of 

 soil taken up haphazard from a farm or from a town with the hope 

 that upon the results of analysis a rule may be evolved for the suc- 

 cessful management of the property concerned. 

 13—6—1907. 



