Many micro-organisms act upon nitrogenous matters and destroy them, in that the substances are rendered less available for higher plants. These are denitrifying agents. There is another class of these micro-organisms, however, that takes nitrogenous food, which is only a little or not at all utilized by higher vegetables, and makes it available plant food. These micro-organisms thus contribute to the fertility of the soil. They oxidize ammonium compounds, from whatever sources they may be had, and form nitrites first and then nitrates. The nitrates are used by common plants. The nitrifying bacteria are composed of two groups of active agents: one group serves to make the first change, namely from ammonium compounds to nitrites; and the other, to change the nitrites to nitrates. The conditions most favorable for their activity are just the opposite for most other micro-organisms. In a soil having much organic matter already decomposed, these bacteria may be practically inactive until the decomposition has passed certain stages. During this transition, the soil is barely suited for crops. Nitrification requires the oxygen of the air; denitrification can go on in a compact soil with the least portion of the atmosphere. So really the soil is cultivated largely to favor the growth and propagation of the nitrifying bacteria. The result of experimentation has shown that this may be facilitated in some cases by denitrification first, and in other cases by stirring the soil for the penetration of the air, and again by applying lime to the soil to overcome the acidity. Professor Burrill recently said, “Some day farmers will come to understand that specialists working in the laboratory, and for years gazing through microscopes, are gaining knowledge for them.”
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.
This is indeed a day of almost excessive specialization in science: Great things have been accomplished by the intense method. Some have thought, and spoken their thoughts, that such tended to carry men of science away from the contemplation of a unit or the system as a whole. Not a few have argued, perhaps with reason, that the great generalizations, as for example Darwin’s theory of evolution, were no longer to be hoped for. It is impossible for any single brain to follow the details of the varied branches of science. It is rare that one man pretends to know the detail of that division of science to which he gives attention. It is equally true, however, that many systematic minds are gathering, collating and publishing in readable form accurate summaries of details in the several branches. Men of broader vision are gathering these authentic digests and offering concepts, which encompass the phenomena of the Universe.
Such have been hinted at as the efforts of some to do away with what we have been pleased to term axiomatic truths. Whether this be desirable, is really of no moment. The facts point to the present movement of efforts to simplify matters. The most beautiful things after all are the simplest. This idea, of course, should not convey the impression of being boldly plain.
“THE MESSAGE OF THE VIOLET.”
By G. D. G.
Down the long corridor swept the theater-goers, men in the sober black and white of evening clothes, women in the brightest of theater gowns. Debutantes paused to chat with college men as they found their way to boxes and orchestra chairs; bachelors stopped to talk of the affairs of the day before taking their places in the front rows. The old playhouse was fast filling, for it was “The Princess of Tyrolia” that night.