These baser modes of life appear to have been rather insidiously developed, as though there had been some hesitation at even the smallest departure from the normal. Of course we must not forget that plants, while living things, are never reasoning ones, and that good and evil and all other qualities that are ascribed to plants are perfectly foreign to them. Throughout this book, and in many others, the habits of plants are spoken of as base, for instance, or good. What is actually the fact is that nature works in truly marvelous ways, and to our reasoning faculties these adjustments seem clothed with attributes they do not really possess. But the description of them in the terms of our everyday speech, the translation of their behavior into the current conceptions of mankind, does so fix them in our minds that they cease to be “just plants,” and we no longer put their habits in the category of those interesting things that nearly everyone forgets. One of the first signs of departure from the usual methods of getting food is the association of certain minute organisms at the roots upon which plants, otherwise autophytic, depend for aid in securing nourishment. This characteristic is fairly common, notably in all the plants of the pea family, such as peas, beans, locust trees, vetch, clover, and hundreds of others. If the roots of any of these be examined, it will be seen that attached to the smaller divisions of them are small tubercles from the size of a pinhead to a pea, depending on the kind. These tubercles or galls are caused by and infested with bacteria, the smallest of all plants. The bacteria have the extraordinary power of changing nitrogen into nitrates, which is the only form in which nitrogen can be absorbed by roots. Not only do they accomplish this, but excess nitrogen is stored in the roots by the same agency. It is this fact that has resulted in the planting of vetch and kindred plants for soil enrichment, as each year there is a residue of nitrogen left in their roots and by so much they add plant food to the soil. For hundreds of years farmers have done this, but only quite recently have we known why they did so. The occurrence of bacteria or microbes at the roots of plants is much more common than was formerly supposed to be the case, and many other plants than those of the pea family depend, at least in part, upon them in getting food from the soil. While not wholly autophytic, such plants do make some return for what they gain, as some of them at least pay dividends in extra nitrogen, and all of them provide opportunity for the bacteria to live. The latter play an important part in populating the soil, which is not the comparatively sterile thing it appears to be. Actually it is infested with organisms that play a mighty, if rather inconspicuous, part in the work of preparing the soil for plant growth. These organisms are so minute and the chemical nature of their work is so complicated