observed a whitish substance like mould.” Footnote 9: Journal of Horticultural Society of London, vol. i. p. 11. Although this disease made its first appearance, in the middle of August, 1845, in the Isle of Wight, it had already appeared in Belgium in the same year, a month previously; and although it may have been noticed in other British localities in 1844, it was known in Canada and in St. Helena in the same year to a far greater extent, and in Liège as early as 1842. There are, therefore, good grounds for believing that the European centre was Belgium; but if M. Boussingault was correct in stating that “this malady is well known in rainy years at Bogota, where the Indians live almost entirely on potatoes,” then it is not of European but American origin, and is probably derived from districts not far remote from those whence Europe first received the potato itself. It would occupy too much space to detail the different theories and opinions relative to the causes of this disease to which 1845 and subsequent years gave birth. Suffice it to say, that the lapse of years has silently proved the majority of these to have been fallacious. All such as imputed to peculiar electric conditions, a wet season, or other meteorological influences, the disease which has re-appeared under different conditions and influences, and in seasons remarkable for dryness, are manifestly refuted; whilst its mycological origin has continued to gain adherents, and the gradual accumulation of fresh facts has almost placed it beyond dispute not only that the potato disease is accompanied by, but results from, fungal growth. Unfortunately, this disease has been so prevalent, more or less, during the past eighteen years, that few have been without the opportunity of making themselves acquainted with its external appearance. To this may be added the minute and exact account of its development, as recorded by that excellent mycologist and careful observer, the Rev. M. J. Berkeley, in 1846, and to which, even now, nothing of importance can be supplemented or abstracted:—“The leaves began suddenly to assume a paler, and at length a yellowish tint, exhibiting here and there discoloured spots. More or less coinciding with these spots, on the reverse of the leaves, appeared white mealy patches, consisting of a minute mould, proceeding, either singly or in fascicles, from the stomata, and arising from an abundant branched mycelium creeping in every direction through the loose tissue beneath the cuticle. The upper surface rarely, if ever, exhibits the mould, it being almost physically impossible for its delicate threads to penetrate the closely-packed cells which, being arranged side by side, leave scarcely any intercellular passages. The mould, in a few hours from its first piercing the apertures of the stomata, perfects its fruit, and in so doing completely exhausts the matrix, which in consequence withers. No sooner have a number of the leaves been