Two species, also common, having many features agreeing with each other, are found on the leaves of the maple and the willow. The willow blight (_Uncinula adunca_, Lev.) is found irrespectively on various species of poplar and willow (fig. 221). In size and external appearances, to the unaided eye, it seems scarcely to differ from the preceding, but more minute examination will show that in the appendages there is an appreciable difference. Still rigid, but no longer aciculate, the tips bent or curved like a little hook, or curled upon themselves (fig. 223), radiating and numerous (fig. 222), and at length tending upwards. Many sporangia are contained within each conceptacle, each of which is furnished with four spores. The amateur must not be disappointed, if, on examining mature conceptacles with a view to the discovery of the sporangia, he finds only free spores. The investing membrane is very delicate, and disappears generally as the spores are matured. The “blight” or “mildew” which occurs on the common hedge-maple, as well as on sycamore leaves, is exceedingly conspicuous when occurring on the former plant. The whole bush often presents a hoary appearance as if sprinkled with powdered chalk. In the spring, the under surface of the leaves of the same plant are liable to become hoary from another cause. The whiteness occurs in patches, has often a pinkish or violaceous tint, and glistens like hoar-frost. This affection of the leaves was, at one time, believed to be produced by a fungus which was called _Erineum acerinum_, but now it is regarded as a diseased state of the tissues. In the maple mildew, both surfaces of the leaves are alike affected, and the little, dark, point-like conceptacles will be found studded over both. It is not uncommon to meet with very white leaves, caused by the mycelium, but which bear no fruit. The appendages in this species are shorter than in the last (fig. 225), and the tips are bifid (fig. 226), or divided into two short branches, each of which is bifid, and uncinate or hook-shaped (fig. 227). The conceptacles contain not less than eight sporangia, each of which encloses eight spores.