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always there; and I at once suspected that it was, and is, and always will be, a condition precedent to fungoid disease in the plant. I suspect that even now, old age—too prolonged propagation from cuttings—is at the bottom of the vine grower's troubles, and several of them to whom I have explained the matter, fully agree with me; and one at least is preparing to grow the vine from the seed. Also the sugar planters, who it seems always propagate from cuttings, will of necessity have their own pestilence in due time; that is, if vegetative multiplication is not an equivalent to sexual reproduction.
Returning now to the assertion at the Meeting of the British Association, that seedling potatoes are as subject to the Disease as old varieties—in the Autumn following that Meeting (1874,) I advertised for potato berries, and obtained them (all from new varieties) by the ton, at Five Pounds per Ton. I lost about nine tenths of them by treating them as directed in the books, but I had millions left; enough to have re-stocked Europe in a few years.
In the spring of 1875, I selected a field as favourable to the development of the parasite, as could be found anywhere perhaps;—a piece of slob land on Belfast Lough which had been heavily manured as a kitchen or market garden for many years; in which since 1845, there has been probably every year more or less old potatoes planted, and more or less disease. This field is fat to rankness, full of immense worms, slugs, and larvæ, and I prepared it in the usual way for growing “sets” of the plant—that is, in drills; using as manures, here guano, there bone manure, in another place stable manure; and in another place no manure; a variation of treatment which produced no apparent variation in results. In these drills I planted here and there the “sets” of four or five old varieties of the plant, which were certain to become diseased, and did become diseased. In this same field, alongside and among these old “sets,” I planted about five thousand plants, obtained this same season from the seed. When both were ripe (the seedlings and the old) I dug them up, and allowed them to lie side by side on the soil for a few days, in order that the Peronospora Infestans (the parasite) should have the fullest opportunity of making its attack. And what was the result? Exactly what I had expected. I found that
