It is somewhat gratifying to find your amateur correspondents inquiring for more practical knowledge with regard to the more economical cropping, and better use of the vegetable garden. This subject has long been behind the march of improvement which has characterised some other parts of Horticulture, and it appears not a little singular, when we consider the utilitarian age we live in. While there has been an intense desire to ransack Europe for new Pears, etc., and some cultivators can boast of exhibiting on the same table, from two to three hundred (said to be) distinct varieties, - while the minds of many have been puzzled for a new idea, in the arrangement of a trim bouquet, - the vegetable garden has been left with no further notice or forecast than merely planting and sowing; little or no regard being paid to rotation of crops, or how they may be arranged so that one may succeed another, during the season, without half of the ground lying waste. Surely this is of sufficient importance to receive attention, particularly if we consider the pecuniary results. The Vegetable Garden is in itself a pleasing object, if well attended; but we must also look for more substantial gratification.

The capital spent in this department should be returned, with interest, and the general health promoted, by the wholesome produce which it can be made to bring forth. Therefore, a few general remarks may not be out of place, and will be something toward answering the request of your correspondent in the August issue.

When a man is first domiciled in the wilderness, he very naturally looks around him for the best spot, the most advantageous position upon which to grow food, and in his then primitive state he is induced to go the readiest and least expensive way to work, which will, of course consist in roughly breaking the sod. He is satisfied with the greater or less produce, according to the natural fertility of the soil, without troubling himself about making the most of a small space, or how many crops he can get off the same piece in a season. But in more densely populated localities, where land has become high-priced and restricted in extent, and where the first setnotion that land most lie "fallow" part of the time in order to maintain its capabilities to produce, and that without this we labor in vain. Such a theory may do well enough for those who are contented with half a cropped garden, where the weeds are often the most prominent objects, but it will never satisfy the energetic observing mind of a good cultivator; nor can he be convinced that such a mode of procedure can be made to pay.

That "fallowing" is of service under some circumstances, may be reasonably admitted, as the getting rid of the multitude of the seeds of weeds, and mellowing of the soil, by frequent plowings and harrowings after the first turning up; but in these days of progress we find that agricultural chemistry teaches us that by supplying the deficient elements, good drainage, proper rotation and judicious tillage, we may keep the same plot always occupied, or at least during the time when the temperature is high enough to forward vegetation. Now, if this be true, (and it would be no difficult matter to furnish the proof,) there is no occasion to have any part of the vegetable plot lying waste, except during the winter season, and even then a portion may be employed. But this is not to be accomplished without forethought, as each kind to be grown must be considered with reference to its time of duration, so that it may be known how far one will interfere with the other, or how soon the ground will be clear of the present to make room for the future crop.

If Peas are sown in rows six feet apart, Celery may be planted between each row; and before the latter require earthing up, the former will have perfected their crop, and may be removed. Spring Spinach and Turnips will answer between the rows of Peas, if sown early, and may precede the Celery. A crop of Ruta Baga may follow early Potatoes; or winter Turnips may succeed Potatoes which are second early.

After a crop of Early Cabbages the last planting of Sweet Corn may be put in. Rows of early Lettuce, Radishes, and such like, if placed six or seven feet apart, will not interfere with Water-Melons, as the Melons will be progressing and the Lettuce, etc, will be fit for the table before the vines meet Cauliflowers, also, if planted in rows the same distance, will not interfere with Musk Melons. Squashes if sown among the earliest crops of Sweet Corn, will not be injured if the corn stalks be removed when the heads are past use. Winter Cabbage will do planted between the rows of late Potatoes. Beets for winter, or fall and winter Cauliflower, may re-occupy any vacant ground in the middle of July.

It is desirable that no fruit trees be planted where esculents are grown; but where this is unavoidable, the smaller kinds, as Gooseberries and Currants, may be put beneath the larger ones. Cucumbers, Gherkins, etc, will do in the shade, yet not so well as in an open exposure, but will fill up vacant spaces under trees, for the sake of economy. These are only a few examples, given to illustrate the method by which the whole of a Vegetable Garden may be kept well stocked through the season, and it will be readily seen how much further the subject might be pursued. To give more would only appear like an endeavor to establish something like mechanical rule, a thing that gardeners should in all cases avoid. Be ruled by circumstances, observation and foresight, and there is little occasion to fear failure attention as regards manure and trenching; but as a genera] thing, if proper rotation is practiced, several crops may be taken off the same piece with one application of the fertilizing material; and a well considered plan of action in advance will enable the operator so to arrange and prepare the various plots, that the fall (which is the best) or early spring manuring will suffice, without the necessity of having to litter over the garden during the summer season.

The rotation of crops, or growing different kinds in succession, is a practice that every person who is acquainted with cultivation, acknowledges to be essentially required. Although correct chemical analyses shows that all plants are composed of the same elements, with very slight differences, yet these minute variations are sufficient to act very powerfully; enough so to be in many cases a mystery. Agricultural chemists often give us truthful accounts of the integral parts of different plants, and we might infer that if the soil contains something like relative proportions of these materials, that success must be certain. This, it is true, is an index, by which we may in part be guided. We must, however, recollect that a living plant is somewhat of chemical laboratory, and it is not yet determined in what proportions the different parts as found in the structucture, are taken up, or whether some of them are not manufactured by the plant itself from more simple elements. There is yet much need of investigation on this point, notwithstanding the great advancement that has been made of late years. In the mean time, it is well for us to leave all such weighty experiments to those who have time and opportunity to carry them out, and fall back upon established facts.

It is well known that plants decompose carbonic acid by the leaves, and assimilate the carbon in their structure, and we may with propriety suggest that, as this gas is heavier than the atmosphere, those vegetables which have a great amount of succulent leaf and near the ground, are capable of absorbing a large quantity, and very likely more than they really require, consequently a portion of this may be given out by the roots, and remain as nutriment for future crops of a less absorbing character. After a very careful observation for many years, I am led to believe in this theory, and constantly make use of it in my own practice, with success. To make the matter more plain, a crop of Turnips or Beets may be succeeded by Peas, and Spinach by Corn, etc. It may be admitted that the manuring between crops, will in some cases appear to counteract this presumption, but I have always found the manure when so applied, to act more powerfully if the above kind of rotation has been observed.