A correspondent of a daily paper gives the following interesting account of California fruits:

The annual fairs of the Mechanics' Institute and the Horticultural Society, united, are now open at San Francisco. What we have written of the fairs at Marysville may suffice as a general description of this, except that here is no exhibition of cattle, and no racecourse. It is not an agricultural fair. The display of fruits is much larger, because this is the great central depot for the State. In no Eastern State can an exhibition be got up of fruits of so vast variety, and of specimens of such perfection, as to show not a blemish. In no country is there such difficulty in awarding premiums, because the general excellence is such that it is only 6hades of difference which determine the awards of merit. We shall not go through a list of varieties, because you can scarcely name one that is not represented; but we may give some peculiarities that will interest every horticulturist. We were in a position that gave us the means of exact information. The apples are from trees seldom exceeding five years old from the graft.

Whether in fineness of texture, or in fine flavor, California apples fully equal those of Oregon, and we cannot find much if any difference in comparing the general run with the apples of Eastern States. There is one peculiarity of importance, viz: about two thirds of your winter apples become autumnal fruit here, occasioned by the uniformity of the temperature and other climatic causes. This is against the profitable account. By reason of this, in selecting the best winter apple for the premium, a score of undoubtedly fine so-called winter varieties had to be rejected as autumn apples, and the Northern Spy was decided to best combine, with other desirable qualities, that of keeping for spring use. The Early Pearmain took the prize as the best summer apple. But as the season is over for summer varieties, the best is probably not on exhibition. The Gravenstein is the fall apple pronounced the best. We hope to send you pastel drawings of these, colored to life. Size is not a material element before the judges, but longevity and general qualities. It is found that different varieties of apples are adapted to different soils and exposures. What does well in Napa, may not do at all at Petaluma, for instance; and this remark applies to other fruits.

We attended the convention of fruit-growers, where, in the usual practical way of getting at things here, each variety of every species of fruit was culled, and growers were interrogated as to their experience. Everybody in California talks with ease and to the point, and everything that is known is thus elicited. You would be surprised at the intelligence and ready wit that sparkle at such conventions here, tempered with all courtesy and good humor. There is a keen relish for a little bit of fun, and persons who come here to speak, should cultivate that branch of eloquence.

Pears are in large display. This is especially the home of the pear, the plum and the grape. These fruits have no enemy in California. The old mission trees of half a century, and the vines of nearly equal age, hang now as full as at first, without a speck to denote deterioration. The Bartlett . takes the premium, but there are plenty of nearly equal excellence; The flavor of the pear here is superior to that of the States. The plum here is less acid and more flavory. Of the peach opinions differ. We should say, as of the strawberry, it is scarcely so well flavored as in the East. But, in all other respects, these two fruits are very fine. The peach does not make profitable production in what is called the Bay country; that is, wherever exposed to the unceasing winds that sweep the country for some thirty miles east of San Francisco; and grapes may be included. These last are also injured by the summer fogs peculiar to the coast. The best section for peach and grape is undoubtedly around Sacramento; and thence, over a vast extent of country east towards the mountains, and south to Lower California. Los Angeles has long been celebrated for grapes, and it is, perhaps, the most profitable section for their culture.

Nectarines are abundant; but this fine fruit comes with the peach, and the retail market has not made an adequate opening for it. Apricots are early, and find quick sale. Prunes are on exhibition, dried in the air. These show how well adapted is this climate for drying fruits to export. They can be cured in the open air, and out of the too drying rays of the sun. There is no danger of injury from rains or dews while being cured, and for these reasons California dried fruits will take the first rank in the market of the world. The pomegranate, though exhibited, is a rare fruit. The climate is exactly suited to its growth, but, like the orange, the almond and olive, cultivators have not seen any prospect of a profitable market for it. The almond is the fruit-stone of a certain kind of peach whose fleshy part is not palatable. At this time the loaded trees exhibit a curious appearance, the almond peach being bursted, and showing the almond stone within the cleft, clean and ready for market the moment it falls out. The California white walnut is superior to the European in one respect; it leaves upon the palate no bitterness after eating it.

The tree grows wild along the Sacramento. The Lawton blackberry has found its way here, but the exhibition proves that it is equalled by two varieties natives to this country. It is hard to beat. There are very few quinces at the fair; but these are fine and free from any blemishes. We see everywhere plants of trees, but scarcely any of this fine preserving fruit. It may be that this season has been unfavorable From this display one must set down California as a country in which fruit must ever hereafter be plenty. It is now, and it has been, the most healthy country on the globe, when fruit was not to be had, and the accession of this wholesome element to the diet of the people, gives earnest that the general sanitary condition will be sustained and improved, San Francisco, Scpt 18, 1858.