There is much in the action of lime in the soil that is not known, but all that we really need to know is simple and easily comprehended. The purpose of this little book is to set down the things that we need to know in order that we may make and keep our land friendly to plant life so far as lime is necessarily concerned with such an undertaking. Intelligent men like to reason matters out for themselves so far as practicable, taking the facts and testing them in their own thinking by some truth they have gained in their own experience and observation, and then their convictions stay by them and are acted upon. The whole story of the right use of lime on land is so simple and reasonable, when we stick only to the practical side, that we should easily escape the confusion of thought that seems to stand in the way of action. The experiment stations have been testing the value of lime applications to acid soils, and the government has been finding that the greater part of our farming lands is deficient in lime. Tens of thousands of farmers have confirmed the results of the stations that the application of lime is essential to profitable crop production on their farms. The confusion is due to some results of the misuse of lime before the needs of soils were understood, and to the variety of forms in which lime comes to us and the rather conflicting claims made for these various forms. It is unfortunate and unnecessary. The soil is a great chemical laboratory, but exact knowledge of all its processes doubtless would enrich the farmer's vocabulary more than his pocketbook. We are concerned in knowing that lime's field of usefulness is broad in that it is an essential plant food and provides the active means of keeping the feeding ground of plants in sanitary condition. We want to know how it comes about that our soils are deficient in lime, and how we may determine the fact that they are deficient. We wish to know the relative values of the various forms of lime and how we may choose in the interest of our soil and our pocketbook. The time and method of application are important considerations to us. There are many details of knowledge, it is true, and yet all fit into a rational scheme that shows itself to be simple enough when the facts arrange themselves in an orderly way in our minds.