CHAPTER IV EVIDENCES OF ACIDITY _Character of Vegetation._ The character of the original forests is determined much by the lime-content, and the practical man, when buying a farm, rates its productive power by the kinds of timber it has produced. The black walnut, ash, shellbark hickory, black and white oak, sturdily grown, evidence a soil rich in lime, while the pines, small blackjack and post oaks, and the chestnut are at home in non-calcareous soils. The latter class of lands gains nothing in lime as time passes, and the timber continues to be a sure index, but in the former class the surface soil may have lost enough lime to limit crop production materially while the trees continue to find in the subsoil all that they need. It does not follow that the land has gone down in value to the naturally lime-deficient class, but its power to produce is impaired, and will remain so until there has been restoration of its original alkaline state. _Sorrel and Plantain._ We determine quite surely the state of the soil by observance of the vegetation that roots in the surface soil and the immediate subsoil. Sorrel is a plant popularly associated with soil acidity, but this is not through any dislike for lime. It has been observed growing in the edge of a heap. Its presence suggests acidity because it can thrive in a sour soil that will not produce plants of value which on even terms could crowd the sorrel out. There is constant competition among plants for food and water and space, and some of our worst weeds are not strong competitors of clover and grass where soil conditions are not unfavorable to the latter. Blue grass, the clovers and timothy give a good account of themselves in a contest with sorrel and plantain where lime is abundant. This does not mean that the seeds of these weeds may not be so numerous that an application of lime cannot cause the clover and grasses immediately to take the ground to the exclusion of other plants, but it is true that the crowding process will continue until the time comes in the crop rotation that these weeds cease to be feared, and clean sods can be made. It is the absence of lime that permits such weeds to maintain their reputation for good fighting qualities. [Illustration: Limed and Unlimed Ends of a Plot at the Ohio Experiment Station] [Illustration: Effect of Finely Pulverised Limestone on Clover in a Soil Having a Lime Requirement of 5200 Pounds of Limestone per Acre at the Pennsylvania Experiment Station]