[18] This blight is mentioned here on account of its affinity to the former.
7. Æcidium berberidis (Barberry-rust) is here referred to, from the opinion prevailing that it is the cause of rust and mildew in wheat. We can no more believe that the barberry-rust would produce rust in wheat, than the rust of any other plant would do so; for nearly all plants are affected with some kind or other of rust. This epiphyte, too, is very different in structure from wheat-rust. Still, that wheat growing under a barberry hedge may be more blighted than in the rest of the field is quite true; and so it is with wheat grown under any kind of hedge. High fences are known to favour wheat blights; open, exposed, well-cultivated positions, when not too elevated, and without trees or hedges, being those in which the best wheats are grown.
8. Cladosporium herbarum (Corn-ear Mould) is a brown-coloured mildew, mostly occurring on the exterior of the chaff-scales of wheat, but common to many plants in a state of decadence. It consists of greenish or blackish tufts, which appear on the outside of the chaff-scales of wheat under the two following conditions:—
On wet soils, where the ears appear to have been prematurely starved.
On dry sands, where long-continued drought has caused some ears to wither and die before the seed was fully formed.
In both these cases we see that the plant has been previously injured. The decay commences under alternations of moisture and drying, and hence the fungoid attack. Here, then, the conditions necessary for preventing will be deep cultivation and a due pulverization and mixture of the soils.
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.
13. Oïdium abortifaciens (Ergot); Secale cornutum (Ergot of Rye).—The black horn-looking spur which occurs in rye and other grasses was formerly looked upon as a distinct fungus; now, however, it is known to be a diseased or malformed condition of the grain or seed, resulting from an attack by an oïdium on the immature seed.
Most of the cereal and even the meadow grasses are liable to attacks of ergot, which is increased by cold damp fogs and a moist condition of the atmosphere, the difference of the size of the spur being in accordance with the size of the affected grass seed. Thus, in rye we have seen spurs more than an inch long, while in the cock’s-foot grass it is seldom a quarter of an inch.