We some time since gave a theory in regard to potato rot, and a novel and curious method of preventing the same by the insertion of peas in the seed potato. We now find in the Buffalo Commercial an account of another cause for this destructive disease, discovered by Mr. Alexander Henderson, of that city. He thinks it is produced by an insect, the egg of which is laid on the skin of the potato, is invisible to the naked eye, but may be detected with a microscope, and is planted with the seed potato. .The egg is hatched in about six days, and the young insect remains in the ground until he gets wings. In the meantime he is engaged in stinging the tubers, each perforation poisoning the root and begetting the rot. While yet in the ground, and as early as the tenth day of existence the young insects' cohabit, and from the great rapidity with which they propagate, Mr. H. arguee that the egg is deposited before the first emergence from th, ground, although in case of cold wet weather, the insect sometimes leaves the vines and returns to the tuber.- Only a few days arc required for the entire destruction of the vine. The insect is remarkably industrious, but the destruction of the vine does not affect the tuber except to stop its growth. The Commel'cial gives further particulars, as follows : " Mr. Henderson states that he discovered the bug on the vines in 1850, but thought it was confined to them. During the last year he has found it on the tubers, and watched its effect upon them. It appears on the vines in from two and a-half to three months after planting, according to soil and manurea richly manured soil producing the perfect insect sooner. "A short time since Mr. H. left at our office a glass jar containing a sound and healthy potato plant, with which were confined some six or eight of the insects alluded to. The insect itself we cannot describe scientifically. It is about half the size of the common house fly, of a brownish color, has six legs, two pair of wings, two antennae, and a long strong proboscis. The insect was actively engaged upon the various portions of the plant, and in the course of twenty-four hours it waa evidently diseased, the leaf becoming brown and mouldy, while the stalks, in the course of two or three days, suffered a putrescent change ; in four days some of them fell over by their own weight, the stalks being swollen and softened in some places quite to a jelly of a sickly green color. "If we put a stop to the planting of the egg with the seed potato, we stop the propagation of the insect. The egg being invisible, any means applied should be thorough, and reach the whole surface of the root. Mr. H. states that by sprinkling quicklime over the potato, as it is cut for planting, the moisture will dissolve the lime and bathe the tubers in a caustic alkali, which will destroy the eggs. At this time of the year the ravages of the insect may be prevented by packing the earth around the tuber firmly with the foot, which will smother the insect."