They will do this in addition to the food supplies which they furnish, hence they may be made to supply this most important element of fertility, and by far the most costly when purchased in the market, virtually without cost. The favorable influences which these plants thus exert upon crop production is invaluable to the farmer. They make it possible for him to be almost entirely independent of the nitrogen of commerce, which, at the rate of consumption during recent years, will soon be so far reduced as to be a comparatively insignificant factor in its relation to crop production. It is possible, however, and not altogether improbable, that by the aid of electricity a manufactured nitrate of soda or of potash may be put upon the market at a price which will put it within reach of the farmer. The power of legumes to increase the nitrogen content in the soil should allay apprehension with reference to the possible exhaustion of the world's supply of nitrogen, notwithstanding the enormous waste of the same in various ways. The more common sources of loss in nitrogen are, first, through the leeching of nitrates into the drainage water; second, through oxidation; third, through the use of explosives in war; and fourth, through the waste of the sewerage of cities. When plant and animal products are changed into soluble nitrates, they are usually soon lost to the soil, unless taken up by the roots of plants. When vegetable matter on or near the surface of the ground is broken down and decomposed, in the process of oxidation, there is frequently much loss of nitrogen, as in the rapid decomposition of farmyard manure in the absence of some material, as land plaster, to arrest and hold the escaping ammonia. Through explosives used in war there is an enormous vegetable loss of nitrogen, as nitrate salts, which should rather be used to preserve and sustain life than to destroy it. The waste of nitrogen through the loss of sewerage is enormous, nor does there seem to be any practicable way of saving the bulk of it. In many soils the germs which produce nodules are present when clovers are first grown on them. But where they are not present, the clover plants have no more power to gather nitrogen than wheat or other non-leguminous crops. But since in other soils they are almost entirely absent, how shall they be introduced? The process of introducing them is generally referred to as a process of inoculation, and soils when treated successfully are said to be inoculated.