The following article was read at the meeting of the Cincinnati Horticultural Society, on the 17tb of July, and directed to be published:

From recent and careful investigation, I am inclined to believe that the " rot," so destructive to the Catawba grape in our vineyards, has its origin in the same cause that produces the "mildew," and is in fact only that disease in another form.

In examinations with a magnifying glass I have discovered a small cryptogamous plant or fungus, growing on the stem that attaches the berry to the stem of the bunch in diseased specimens. This fungus, by obstructing the circulation of the sap, causes the berry to assume a dark mottled appearance, then to turn black, shrivel, and fall off.

In some bunches all the berries are thus destroyed, in others about half, and in many but lew.

Perhaps the "speck " or "spot" may be attributed to the same cause.

The "mildew." as we have generally known it, first appears about the lime when the grapes attain the size of small peas, blighting occasionally the whole bunch, stem and all - but usually only the lower portion of it.

There is no mistaking the disease, for it covers the part affected as if dusted with flour. - In a few days the berry and stem turn black and crisp. When the grapes become larger, they appear to be better able to resist the influence of mildew, and the part least exposed to the light and air, the stem of the berry, is then affected, and the fruit finally destroyed by what is termed the " rot." The stem of the bunch, being by this time hard and strong. Is not injured, and remains attached to the vine, while the berries fall off.

These diseases are supposed to be produced by sodden changes in the weather from hot to cold, or the reverse - from heavy fogs - from warm showers succeeded by a hot sun, with but little electricity to purify the air, or wind to drive away the noxious exhalations arising from the earth.

An excess of moisture about the roots of the vine in a stiff clay soil, retentive of moisture, may subject the plant to mildew, as also excessive manuring, rigid summer pruning, or deep plowing or hoeing of the vineyard in summer.

Experience alone can prove whether any or all of these conjectures are right.

So much for cause and effect ; now for the remedy. In volcanic countries, where the finest grapes are grown, we hear no complaint of mildew. Perhaps an application of ashes and sulphur to our vineyards, by supplying to our limestone land some of the properties of the volcanic soil, might, to some extent, prevent mildew and rot. I therefore recommend as an experiment, on a part of the vineyard, a light top-dressing of ashes in the spring, before hoeing; and to scatter flour of sulphur over the ground, and a part on the vines, the last week in May or the first in June, and again about the first week in July. These applications may possibly prevent mildew to some extent; they can certainly do no harm. Sulphur is freely used in vine-houses to destroy mildew on foreign grapes, and ashes are strongly recommended by one of our most intelligent cultivators, Dr. L. Rehfuss,.as a means of supplying to the soil the alkalies drawn from it by the grape.

I have tried sulphur on one square of my own vineyard this season, with good effect, although it was not applied at the proper time.

I would also recommend to avoid stirring the ground after the first hoeing in April or May, to omit high manuring, and to avoid too rigid summer pruning, as all or either may, perhaps, cause injury to the crop of fruit.

I make these suggestions with diffidence, being aware that I am addressing vine dressers of more experience than myself; but I respectfully refer such to my own vineyard for an example of the practical results of my recommendations to others.

In the culture of our native grapes we have much to learn, and it is only by careful and judicious experiments that we shall attain the right knowledge at last. R. Buchanan. Cincinnati, July 17, 1852.