Trefoil and some other allied plants are attacked by another species, characterized by Dr. de Bary as _Peronospora trifoliorum_, which we have found rather plentifully in some localities on lucern. THE PARSNIP MOULD (_Peronospora nivea_, Ung.) is found on many umbelliferous plants; but its attacks upon the parsnip are most to be deplored, because it injures and ultimately destroys an article of human food. The plants infested with this parasite are first attacked in the leaves, but afterwards the roots become spotted and diseased in a similar manner to the potatoes attacked by its congener. The disease has not hitherto been so general with the former as the latter; but in some districts it has been far from uncommon. The fertile threads are collected in bundles, erect, and not so much branched as in many other species. The acrospores are subglobose or ovoid, and papillate at their apices. This species is sometimes called _P. umbelliferarum_, and sometimes _P. macrospora_. Generally speaking the average humidity of a season but little affects the production of parasitic fungi. In a dry season, like that of 1864, we found as many species, and these as flourishing and numerous in individuals, as in a proverbially wet year. Such is not the case, however, with the moulds under notice, or such fungi as are reproduced through the medium of zoospores: these are undoubtedly less common in a very dry season; but it must be remembered that a single shower is sufficient for the development of zoospores, and occasional showers or heavy dews will speed them on their course of destruction as readily almost as continuous moisture. The large fungi, on the contrary, become very limited in numbers when the weather is unusually dry. SPINACH MOULD.—Spinach is likewise liable to suffer from the establishment of a mould upon the under surface of the leaves: unfortunately this is not unfrequent, and has been known in England certainly for the last fifty or sixty years, since it was figured by Sowerby in his “British Fungi” as many years since. We have lately seen a bed of spinach, utterly destroyed by this fungus; whilst on another, not twenty yards apart, not a spotted leaf could be found. This mould is the _Peronospora effusa_ of botanists; it occurs also on some species of goosefoot (Plate X. fig. 215), and probably on knotgrass. To the naked eye it appears in pale purplish-grey patches, which, when examined microscopically, are found to consist of dense bundles of branched threads, bearing ellipsoid acrospores, the membranes of which have a violaceous tint. The oogonia produced upon the mycelium vary considerably in size. The oospores are of the character delineated in our plate (Plate X. fig. 214).