Certain it is that plaster renders plants less palatable to insects, and, so far as the writer's experiments extend, it is fatal to many of the fungi family. To obtain the best results, the vines of potatoes should be dusted with plaster as soon as they are fairly through the soil, again immediately after the last plowing and hoeing, and, for reasons hereafter given, at intervals throughout the whole growing season. The first application may be light, the second heavier, and thereafter it should be bountifully applied, say two hundred pounds per acre at one sowing. THE POTATO-ROT--ITS CAUSE The year 1845 will ever be memorable by its giving birth to a disease which threatened the entire destruction of the potato crop, and which caused suffering and pecuniary ruin to an incredible extent throughout Europe. The potato, at the time of the appearance of the potato disease, was almost the sole dependence of the common people of Ireland for food. That over-populated country experienced more actual suffering in consequence of the potato disease than has any other from the same cause. Although this disease has never, in this country, prevailed to the same ruinous extent that it has in some others, yet we are yearly reminded of its existence, and in some seasons and localities its destructive effects are seriously apparent. The final or culminating cause of the disease known as the "potato-rot" is _Botrytis (peronospora) infestans_. This may be induced by many and various predisposing causes, such as feebleness of constitution of the variety planted, rendering them an easy prey to the disease; by planting on low, moist land, or on land highly enriched by nitrogenous manures, causing a morbid growth which invites the disease; also by insects or their larvae puncturing or eating off the leaves or vines. But by far the most wide-spread and most common cause of the disease is sudden changes of atmospheric temperature, particularly when accompanied by rain. Drought, though quite protracted and severe, unless accompanied by strong drying winds, and followed by sudden and great reduction of temperature, seldom affects the potato seriously. It is not uncommon in the Northern States, during the months of August and September, for strong westerly winds to prevail for many days in succession. These winds, coming from the great American desert, are almost wholly devoid of moisture, and their aridity is often such that vegetation withers before them as at the touch of fire. Evaporation is increased in a prodigiously rapid ratio with the velocity of wind. The effects of the excessive exhalation from the leaves of plants exposed to the sweep of such drying winds are at once seriously apparent.