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Potato Disease. — It has struck me that the following fact may be of some value to some of your correspondents who talk about the necessity and desirableness of getting Potatoes new from the original stock in South America? I have a considerable quantity of this much to-be-desired stock, obtained in the following manner.

In the spring of 1835 (the autumn of the S. hemisphere), Mr. Darwin collected some seeds from ripe tubers, in the Cordillera of central Chili, in a most unfrequented district, many miles from any inhabited spot, and where the plant was certainly in a state of nature. These vegetated under Professor Henslow's care in the year 1836 or 1837, and in that year or 1838, a tuber was given me by Mr. Darwin. It was either three or four years before the Potatoes from it became eatable. They are now good both for eating and keeping, and good bearers. I had them growing last year among many other kinds; and as they are a late variety, they had not ceased growing when the disease appeared in Cheshire. They fared exactly the same as other kinds, having the blotch in the leaf and a few tubers decayed. This year the haulm was destroyed totally, in the same manner as all my Potatoes were; and on taking up the tubers I find about the same number diseased as in other kinds, I fear this decides the point as to the uselessless of procuring seed from even the fountain head—the wild stock itself. As I have intruded thus far, I will add a few words as to the result of my own experiments and observations last year and this. I felt no doubt last year that the disease was communicated from the south of England—for this reason: when | first observed it in the south, we had not a speck upon the leaves, nor an unsound Potato. This continued long after grievous complaints in the south, until at length it seemed to gradually creep to us, and kept proceeding northward, but did not work very far in Scotland. None of my early Potatoes, and scarcely any second earlies, were touched, being raised before the disease came to us; the second earlies were, however, spotted in leaf. The produce of those early Potatoes this year was little injured in the tubers; bot the haulm was destroyed. The second earlies of last year, of which the foliage only was slightly specked then, have been this year almost totally destroyed, after yielding an abundant crop, but of which the tubers almost all decayed. I have this year crops of seedling Potatoes— autumn sown, early and late in the year, with and without manure, and l can see no difference in them. Some crops rather better than others in the tubers; but of all, the haulm totally destroyed, and most rapidly in the best growing crops. I see that some of your correspondents state that in crops of which the haulm was destroyed, they could see no disease in the tubers. May not this have arisen from the diseased tubers being quite rotted away? I have seen this the case, so that you could not discover them without a very diligent examination, and the reminder of the crop was to all appearance quite sound. That the disease is sometimes communicated by the air I have no doubt is the fact. Adjoining my Potato field I had some Dahlias, and when the disease attacked the Potato-haulm so virulently as to make the air for a considerable distance most disagreeable, blotches appeared upon the Dahlia-leaves which could not be mistaken. They began similarly, had the white appearance under the leaf, and soon had the same scorched black look. They, however, outgrew it, and if appears quite gone. Whatever may have been the cause and origin of this destructive agent, about which all seem as yet about equally in the dark, does it not seem, weighing all the evidences on the point from your numerous correspondents, that both parties are right—those who say it comes, or rather is promulgated, from within—and those who say it comes from without. This is the conclusion I have come to after carefully watching it last year and this in a great Potato-growing country, and from numerous experiments. You asserted, I think, at one time your conviction that the spot in the leaf never came till decay had commenced in the stem just above the tubers. In many instances I find this correct; but in many more I could not detect the least discolouration or decay in any part of the plant or tuber when the blotch first appeared of a palish hue above, and a mildew look underneath the leaf. I believe this is after the real commencement of disease in the plant, when communicated through the medium of the air; lot I imagine that after that the plant is tainted, and its tubers the following year have the seeds of death within themselves.— W. D. F.