_Characteristics._--The mildew appears in two different stages, one in the spring when the vines are in blossom, the other again later in the summer when the fruit is more advanced. The first stage of the mildew resembles a fine cobweb spun between the flowers of the bunch. If allowed unrestricted sway, the flowers will drop off, the fruit will never set, or set only imperfectly, and the crop will be a great loss or even a total failure. Generally the inexperienced vineyardist does not perceive the mildew until too late. A slight touch to the vine will then bring down all the young fruit or blossoms like a shower, and the stem of the bunch will be seen to be entirely bare, or with only a few scattered berries. This form of the Uncinula mildew has not been as scientifically investigated as would be desirable, and nothing is known as regards its development. It is possibly a primary generation and early stage of the later Uncinula. I believe this form of the mildew is identical with the disease which is called Colure by the French, and which is characterized by the dropping of the young, undeveloped grapes. The first appearance of this mildew is always accompanied by white, salty excrescences on the edges of the grape leaves. Whether they are directly or indirectly connected with the fungus is not known. The later form, the powdery mildew, and the form which has given this mildew its name, appears later in the season, when the grapes are half grown or more. It then takes the shape of fine powder-like patches or blotches on the upper side of the leaves, stems or berries. These spots are of a dull gray or whitish gray color, and smell strongly of mold or mushrooms. If these mildew spots when young are rubbed smooth, especially on the green stems or berries, we see below them, in the epidermis of the vine, the _mycelium_ or stem of the fungus spreading in all directions from a central point, like the roots of a tree or plant. This part of the mildew corresponds with the stem and root of a plant, while the upper, powdery part is the one which produces the spores or the seed, conidia and peritheca, all of which are reproductive organs. The grapes thus attacked gradually dry up or crack open. The leaves are eaten through and dry up, and the whole plant becomes badly diseased, and may even die. [Illustration: Powdery Mildew (Oidium Form), Greatly Magnified.]