The appendages are seldom at all coloured. Within the conceptacle are contained from one to several transparent obovoid sacs, or spore-cases, called _sporangia_, enclosing a definite number of spores (figs. 218, 224, 228, &c.), which vary in different species. In the hazel mildew, for instance, there are two spores in each _sporangium_; in the willow mildew four; in the maple mildew eight; in the grass mildew, and some others, numerous. The tips of the appendages are variable, and often elegant (figs. 227, 231, 233, 234, and 247), sometimes simple and at others symmetrically branched. All the species occur on the still living and green parts of plants, especially the leaves, and are therefore truly parasitic. A pocket lens will show whether any conceptacles are present on any suspicious leaf which may be collected, but high powers of the microscope are essential for their complete examination. It is during autumn, when vegetation begins to languish, that we shall be most successful in searching for specimens. They will then be found almost everywhere, and the white mycelium forms an object too conspicuous for them to be readily overlooked. Botanically, nearly all the species were at one period included in one genus, under the name of _Erysiphe_, a name derived from the Greek, and signifying “mildew;” at the present time they are distributed through several genera, the chief distinctions of which are based upon the form of the appendages. Though personally disposed to question the generic value of such distinctions, it would be imprudent to adopt any other names here than those to be found in recent English works on fungi. The first species in our enumeration is found on cultivated roses. What a deplorable picture does a favourite rose-bush present when attacked by this mildew! The leaves blistered, puckered, and contorted; their petioles and the peduncles and calyces of the flowers swollen, distorted, and grey with mould; and the whole plant looking so diseased and leprous that it needs no mycologist to tell that the rose is mildewed. The conceptacle in this species is minute, and contains but one sporangium, which is one of the characters of the genus in which it is now included, and a more justifiable distinction than the ramifications of the appendages. The mycelium is rather profuse, and the threads or appendages which spring from the conceptacle are simple and floccose (fig. 216). The sporangium contains eight ovate spores. This species (_Sphærotheca pannosa_, Lev.), in its oidioid or conidiiferous form, was for some time known under the name of _Oidium leucoconium_.