While many bacteria do not necessarily render food available for plants, they are most valuable in putting useless matters out of the way. One of the absolutely essential chemical elements for the growth of plants is nitrogen. It is most expensive. It is present in the greatest unavailable abundance, constituting three-fourths by weight of our entire atmosphere, and it is, also, the one element most likely to be deficient in the soil. It constitutes an essential constituent of albumenoid material. Under the influence of the denitrifying bacteria, it is converted into ammonium compounds, which are converted then through the nitrifying agents into nitrates. The nitrates are extremely soluble in water; consequently, there is no tendency towards the accumulation of the valuable food matter in the soil, as the same is leached out. The growing green plant is surrounded by the food that it wants but, as with the Ancient Mariner, there is not a drop to drink. Green vegetation cannot, or only to a limited extent can, absorb and utilize directly the free nitrogen of the air. As a result of a long series of experiments, it has been learned that there grow excrescences, somewhat similar to galls, on the roots of certain plants. These natural structures have a character peculiar to the species of plants on which they occur. In a manner not understood, these tubercles, inhabited by bacteria, are capable of securing sufficient nitrogen from the air for their own growth, when the soil is practically able to furnish none. Other plants, next door, without these nodules, will die of starvation. The number of bacteria in these nodules is very great but, although countless, they are insignificant compared with those in the soil outside. Those within the nodules, however, are specifically different from those without, perform different functions, and appear to be characteristic of the particular plant in which they exist. The leguminous plants, as peas, beans, clover, have these peculiar nodules. Other plants, however, like maize, cotton, wheat, are devoid of these assistants. It has been known for a long time that the fertility of the soil could be augmented by rotating the crops and thus adding nitrogen to the soil by means of these leguminous plants. One of the problems engaging the attention of scientific agriculturists at present is to learn whether or not these leguminous organisms may be made to form tubercles on other plants, as for example corn or wheat. The importance of the successful issue of such experimentation requires no emphasis. While successful results have not yet been reported, something has been learned: namely, the fruit of corn may be very much modified in its chemical composition by breeding. Grain very much richer in nitrogenous matter has been grown by changes in the breeding. Such grain is a better food.