A. J. Downing, Esq. - As the plum has ripened this year some three weeks earlier than usual, and the season is nearly over for taking notes upon it, we propose to continue our notices of southern fruit growing, by some remarks upon its culture, and notices of the varieties tested in this section.

This immediate vicinity is, perhaps, upon the whole, tolerably favorable to the plum. The Chickasaw Plum is found abundantly in every old field, and there is no very serious obstacle to the growth and culture of the improved species. We do not mean that the plum may be abused as the peach is - that you can plant a stone or a tree at random in an "old field," or in a patch of Bermuda grass, and in two or three years therefrom gather an abundant crop - and in case the seed be of a choice fruit, very likely find your seedling of good quality - for such management will not do for the plum, unless it may be the native species. But though the plum requires some care and attention, there are few locations where it does not require as much, or where in the case of a few select varieties, the reward is more sure.

Our chief advantage is a complete exemption from the black knot; which in some parts of the north I have observed, is apparently as fatal to the plum, as the frost or fire-blight to the pear. This disease has never appeared here. In general, our trees appear perfectly healthy, and make a fine vigorous growth yearly.

We are, also, partially exempt from the curculio. He seems to confine his attention very much to Apricots and Nectarines - usually taking the whole crop of these fruits - but of plums, generally leaving enough of the crop not to render it unprofitable, without resorting to shaking the tree, or calling in the aid of fowls or pigs. Our stiff subsoil of clay and gravel, is too difficult to penetrate, perhaps, while the light gravelly loam that often overlies, is, in general, too shallow to give him a quite comfortable protection from sun and frost. But we by no means entirely escape.

In 1849, a frost in April destroyed all our Apricots, Plums, Peaches and Nectarines; and we were congratulating ourselves that the next year we should be free from curculio. As the destruction of fruit was complete, by all theory the curculio should have perished too. Will you believe it, when we state the obstinate imp utterly refused to sacrifice himself, to maintain even this most plausible of theories. It was absolutely certain, we thought, that die he must, yet he did'nt, and in fact, destroyed more fruit, if anything, than usual; so that if poultry and pigs are any protection, as they undoubtedly are, it must be by frightening him away, or rendering his haunts uncomfortable, rather than by any positive destruction to the curculio himself.

But, though exempt from the black knot, and partially so from curculio, we are not without some little troubles of our own. Occasionally a tree, or a part of it,' dies in the same way as the apple, by the sun striking the trunk or branches. The plum is apt to throw out long branches, not much protected by foliage, which are sometimes blistered by exposure, causing the parts above to perish gradually, and if not removed, injuring the general health of the tree. This is not a very frequent disease, and shortening-in the branches, as directed for the peach, will doubtless so clothe the limbs with foliage, as to prove an efficient preventive.

We find another difficulty in the want of adaptation of a- good many plums that are celebrated with you to this climate. You will observe that several classed in your work as best, here bear no comparison in flavor with some others regarded with you as not of the highest quality. We buy new varieties with the probability that at least every other one of those classed among the best, will be good for nothing. Still we know of several kinds of high flavor, and the rest we can let alone now we have the experience desired.

But our greatest obstacle in the culture of the plum, is its tendency, in common with several varieties of the peach, nectarine, Mid grape, to rot before maturing. In a dry season, no matter how hot it may be, the fruit is not in much danger. But in a year like this of warm, abundant and continual rain, the cultivator may expect to lose, in the esse of most varieties, from half to three-fourths of his crop, and of some it may be the whole will decay. He can guard against this only by selecting the varieties least affected.

A good stock for the plum is the Prunus chieasa or wild Chickasaw plum of the country, which I believe is common over all the south, and collar or root grafting on the same is our usual mode of propagation. It sometimes throws up suckers, but they are. easily removed, and it is uniformly hardy and healthy, and as the grafts take kindly, it is perhaps the best. It is a good stock for the garden for it dwarfs the tree, and, as in the case of the pear on the quince, the point of junction should be beneath the surface. The wild sloe, a small austere red plum, fit only for preserving, is sometimes used, but the grafts are sure to over grow it and perish for want of nourishment.

It is proper to state, before proceeding to notices of varieties, that the times of ripening below are for 1852, and will average two or three weeks earlier than usual, as I find by comparing the times of the few set down last year. The abundant rains too this year, may have so injured the flavor of some varieties, that full justice may not be done them. They are described in the order of ripening, and the dates given are when they begin to mature.

1. Chickasaw Plum

Prunus chieasa - A tree or two of this plum should find a place in every garden, of both the red and yellow varieties. The fruit is much enlarged by garden culture - but the best varieties are later than the common ones - leaves lanceolate shape, more like the peach than a plum - branches thorny. Fruit small, (size of Mirabelle in your Fruits, or a little larger,) skin-either bright red or yellow, somewhat translucent, - flesh yellow, very juicy arid sweet, but somewhat astringent about the stone, to which it adheres. Ripe the 20th of May, and lasts nearly a month. From this will doubtless be produced many excellent varieties by culture and crossing. I have met one variety nearly a month later, marked with small yellowish dots, fruit almost the size of Prince's Yellow Gage, and nearly free from astringency. Can species of fruit trees as nearly related as •this and the domestic plum, be crossed with each other Mr. Editor, with any prospect of producing improved varieties? This plum is I believe free from curculio; perhaps the fruit sets too early in the spring for him.