Weeds have a great influence in producing mildew, which perhaps may be accounted for from the fact that weeds are in active growth as the wheat-stalks decline in vigour; and hence the constant evaporation of moisture from the weeds to the wheat is continually re-moistening an ever-drying surface—a most fertile source of mildew and moulds of several descriptions. 6. _Puccinia fabæ_ (Bean-rust).[18]—The brown pustular rust-looking spots on the foliage of beans, and, indeed, occasionally on the stems and pods of beans, are sometimes common to this crop. They are usually accompanied by a lessening both in quantity and quality of this pulse, both in the garden and in field culture, but certainly more generally in the latter. Too gross manuring without well mixing the dung with the soil would seem to be a constant source of the evil. In fact, highly nitrogenized manures appear to favour the development of all this class of epiphytes, just as too much meat might bring about different forms of rash or eruptions in the animal. Weeds, which are too much permitted in beans, here aid in perfecting the mischief; hence, then, we may perhaps take it for granted that the mention of the causes of mischief suggests the remedy. [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.