The nodules in clover plants vary in size, from a pin head to that of a pea, and they are frequently present in large numbers. Bacteria are present within them in countless myriads. They gain an entrance into the plant through the root hairs. The exact way in which benefit thus comes to the clover plants is not fully understood, but it is now quite generally conceded that the nitrogen taken in by these minute forms of life is converted into soluble compounds, which are stored in the tissues of the roots, stems and leaves of the plants, thus furnishing an explanation to the increased vigor. It cannot be definitely ascertained at present, if, indeed, ever, what proportion of the nitrogen in clover is taken from the air and from the soil, respectively, since it will vary with conditions, but when these are normal, it is almost certain that by far the larger proportion comes from the air. But it has been noticed that when soil is freely supplied with nitrogen, as in liberal applications of farmyard manure, the plants do not form nodules so freely as when nitrogen is less plentiful in the soil. The inference would, therefore, seem to be correct, that when plants are well supplied with nitrogen in the soil they are less diligent, so to speak, in gathering it from the air. In other words, clover plants will take more nitrogen from the air when the soil is more or less nitrogen hungry than when nitrogen abounds in the soil. And yet the plants should be able to get some nitrogen from the soil in addition to what the seed furnishes to give them a vigorous start. This power to form tubercles, and thus to store up nitrogen, is by no means confined to clovers. It is possessed by all legumes, as peas, beans and vetches. It is claimed that some of these, as soy beans, cow peas and velvet beans, have even greater power to gather nitrogen from the air and store it in the soil than clover, since the nodules formed on the roots of these are frequently larger. In some instances, on the roots of the velvet bean they grow in clusters as large as an ordinary potato. With reference to all these leguminous plants it has been demonstrated that under proper conditions good crops may be grown and removed from the soil and leave it much richer in nitrogen than when the seed was sown. It is thus possible by sowing these crops at suitable intervals to keep the soil sufficiently supplied with nitrogen to grow good crops other than legumes, adapted to the locality, without the necessity for purchasing the nitrogen of commerce in any of its forms. They may be made to more than maintain the supply of nitrogen, notwithstanding the constant loss of the same by leeching down into the subsoil in the form of nitrates, and through the more or less constant escape of the same into the air in the form of ammonia, during those portions of the year when the ground is not frozen.