9-12. _Botrytis_, _&c._ (Mildew).—Under this head we include a multitude of epiphytes, to which the terms mildew, mealdew, mehlthau (Germ.) are applicable. They appear to the naked eye as patches of white dust or meal on the leaves and stems of the affected plants. With the microscope we see that they are beautifully-organized plants, having a kind of rootlet (mycelium) or spawn entering the tissues of the living plants on which they grow, and delicate pedicels supporting spores at the externally visible portion of the plant. The botrytis of the potato and turnip, the erysiphe or oïdium of the hop, vine, and other plants, are only different forms of mildew, which in some shape or another will be found on most plants. That these attack living tissues is quite certain; but in the case of the potato, the turnip, and the vine, there is reason to believe that they result, to a very considerable extent, from diseased action in their tissues. For example: the botrytis of the potato seems to attack a crop much over-cultivated, on the approach of wet and cold nights after a prosperous growth in warm sunshine. So, the oïdium seems to us to be most abundant on renewed growth after a season of dry weather. Again: mildew in turnips is sure to follow that check which a long season of dry weather brings after a prosperous and vigorous growth. All these circumstances at least show how these attacks are favoured by the conditions which bring disease. So much, indeed, is this the case, that we found, upon experimenting with some cucumbers in a warm stove, that as long as we regularly watered the plants and gave them the requisite air, they kept healthy; but, by neglecting these conditions for a few days, we obtained mildew with the greatest certainty. The remedies against mildew are—to obtain as healthy a growth as possible, and to maintain this with as great regularity as circumstances will permit. Of late years, both the mildew of the vine and the hop have been treated with flowers of sulphur. Dusting the affected hop-leaves with sulphur certainly arrests the mildew in an incredibly short time; and we found that by dusting sulphur from a fine sieve on our cucumber plants, the disease was immediately arrested in its progress. We therefore look upon this as an invaluable remedy in these states of mildew, whether occurring on the vine, the hop, the turnip, the cucumber, or on other plants, as we have frequently seen it in hothouses—a circumstance which shows the near affinity of all those forms of epiphytes, which, perhaps, after all, only vary with the variations in the structure and economy of the different plants on which they occur.