We may, in conclusion, sum up in a single paragraph the different ways in which lime acts. Its action is mechanical, chemical, and biological. It acts on the texture of the soil, rendering clay soils more friable, and exerting a certain binding effect on loose soils. It decomposes the minerals containing potash and other food-constituents, and renders them available for the plant's needs. It further decomposes organic matter, and promotes the important process of nitrification. It increases the power of a soil to fix such valuable food-constituents as ammonia and potash. It neutralises sourness, and prevents the formation of poisonous compounds in the soil. It increases the capillary condition of the soil, prevents fungoid diseases, and promotes the growth of the more nutritive herbage in pasture-land. CHAPTER XXI. INDIRECT MANURES--GYPSUM, SALT, ETC. GYPSUM. In the previous chapter mention was made of gypsum as a compound of lime, but no reference to its action as a manure was made. In the past, gypsum was used extensively and highly valued. It was found to be of especial value for clover; and there is a story told of Benjamin Franklin which illustrates the very striking nature of its action on this crop. It is related that he once printed with gypsum the words "This has been plastered" on a field of clover, and that for a long time afterwards the legend was plainly discernible on account of the luxuriance of the clover on the parts of the field which had been thus treated. _Mode in which gypsum acts._