Dr. Cloud - Dear Sir, - To learn the conditions of success in the pursuit of any object, is certainly a matter of prime importance; even if success might follow, nine times out of ten, without such intelligence. Merely empirical efforts, when many conditions are combined, add nothing to the general fund of knowledge, and can be of no permanent value. To observe, with the utmost care and accuracy, every phenomena presented in the growth of a plant, adds nothing to our comprehension of the conditions of its development. To plant a grain of wheat, or seed of cotton, and record the changes that follow through the periods of its germination and growth, teaches us nothing with regard to the real influences that have operated to produce these results. To describe the soil on which plants grow, and give every element that enters into its constitution, is of no value unless we knew what elements are the active ones in the production of the desired vegetation. After all this painstaking, one may assert that the influence of the moon was the great exciting cause of all these recorded results.

To add masses of fertilizers, and produce large growth, is of little value when the rationale of the action is left out of sight.

A point of the highest import is to determine a single isolated element of success, or point out one injurious or useless agent in our applications. If a plant is growing subject to three distinct agencies, and by the operation of all it will do tolerably well, yet the action of only one of them is the true and only cause of success, one, perhaps, being neutral, the other, we may suppose, positively injurious. To know these facts would certainly relieve the operator of much embarrassment, and make his calling a much more rational pursuit. One single step in this direction of elimination, though a short one, and made with the light of truth shining upon it, is worth a thousand long leaps in the dark, with guidance of complicated experiments, which are perfectly unintelligible to those who make them. That one step is a movement forward; the others may be in all directions, and when the thousandth one is taken we may be at the place of starting.

There are facts in vegetable physiology, that should be of the highest practical interest, which influence most materially the results obtained, but for which, so far as we know, they have neither credit nor regard. Does the agriculturist, in the preparation of his ground, ever take into consideration the kind of roots the plants have which he is to cultivate? In his combination, separations or succession of plants for cultivation, is an imperfect element to guide his decisions and operations. Judging from books on these subjects, we should be led to believe that if there was any difference in the character of roots, it was entirely disregarded in practical applications. To see the almost identical directions given for the cultivation of rhubarb and asparagus, for example, is abundant proof of this disregard. Asparagus is a surface feeder, and wants room and not depth, and it will grow luxuriantly, as we have proved by experiment, on a shallow soil, if plentifully supplied with fertilizing matter and moisture. Rhubarb, on the contrary, is a deep feeder, and to develop its proper growth, requires deep cultivation, and will not succeed without it.

The active roots of the asparagus are, in the main, but a few inches below the surface; while the rhubarb will be found two feet, if the soil is fitted for it to penetrate so far.

Nature has made the roots of cultivated plants on two models or types, and to one or the other of these types they may all be referred. One of these is a main root, running perpendicularly downwards, and sending off new branches from the top to the lowest extremity, the central axis being always the predominant one through which the nourishment passes. The other type is a more or less complete subdivision of the root, immediately beneath the soil, there being no main axis penetrating downward. The first kind is represented by the branching of any tree, from a main trunk; the latter like that of some shrubs that send up numerous stems with no main axis. The first of these seeks its nourishment deep down in the soil, the latter near the surface. The first draws its nourishment from immediately beneath itself, the other literally from a distance. The first is not much injured by removing the surface roots, the latter wholly depends on them, the upper always being the most vigorous. No matter how many varieties there may appear to be, nor how many different names the botanist may give to these varieties in describing plants, yet all fall within one one or the other of these classes, or approach more or less clearly these types.

The deep feeders called tap rooted, the surface feeders called forciculated. There is an evident design in these structures, relating most certainly to the conditions of growth and development of the plant.

The above are facts, and their application may be made useful in a thousand ways, a few of which we will point out.

If a tree is to be set in the neighborhood of a garden, or cultivated field, the tap-rooted variety should be selected. It will seek its nourishment below the roots of field and garden culture, or it may be made to do so by cutting off the surface roots within the reach of any other plant The oak, elm, sweet gum, cedar and pine are of this class. The mulberry, china tree and ailanthus are surface feeders, or with forciciliated roots, and will destroy all within their reach if they grow thriftily themselves, for in cutting off their roots their growth is checked, unless the soil is very rich.

In planting trees to make the thickest shade, a mingling of the tap-rooted and forciculated will greatly contribute to this end. They may be planted much thicker than either could be alone, by planting them alternately. An oak and a mulberry could both occupy the same space that would be required for either by itself. The oak getting its nourishment deep down in the subsoil, the mulberry feeding at the surface, so that they would not interfere with each other, each growing as though the other was not there. Trees with tap-roots are usually tall and make our best timber, while the forciculated are low, with bushy heads. The one is made to resist the storm, although most exposed, the latter keeps near the ground.