ONION MOULD.—Another disease, produced by fungi of the same genus, makes its appearance upon young onion plants in the spring. The mould is called _Peronospora Schleideniana_, and has many features in common with those already described. In this instance the threads are greyish and erect, with alternate branches, not divided by transverse septa, and the spores are obovate, attenuated towards their base (fig. 263). This mould, in some years, is very common and destructive, by preventing the young plants which are attacked from coming to perfection. It is not confined to the onion, but appears on other allied species of _Allium_ (to which the onion belongs). The threads form large patches or blotches on the leaves, and sometimes cover them entirely. It very much resembles the turnip mould, from which the form of the spores considerably differs. This is the same species as that described by Caspary, and afterwards by Berkeley, under the name of _P. destructor_. _Lettuce Mould._—A very similar mould (_Peronospora gangliformis_) is sometimes very common in spring on the under surface of the leaves of the cultivated lettuce, appearing in definite white mouldy spots. By reference to the figure of a portion of a thread magnified (fig. 265), it will be seen that the peculiar form of the tips of the branchlets evidences the distinctness of this species. The oospores are small, globose, and of a yellowish-tawny colour. This mould is by no means confined to lettuces, but has also been found on species of ragwort, sow-thistle, nipplewort, endive, and other composite plants; and has from time to time received numerous names, which it is unnecessary to enumerate. TARE MOULD.—The under surface of the leaves of tares, and sometimes also of peas, is liable to attack from an allied species of mould (_Peronospora Viciæ_). In the spring of 1846 it appeared amongst vetches in some districts to such an extent as at one time to threaten the destruction of the crops; but a succession of dry weather at once abridged its power and limited its mischief. Mouldy vetches and mouldy peas are, especially in moist seasons, evils to which the agriculturist knows his crops to be subject; he may not know, however, that this kind of mould (fig. 266) is of so near a kin to that which has acquired such wide-spread fame in connection with the potato. Another species of fungus attacks the garden pea in damp seasons, forming small depressed brownish spots on the leaves and pods; but this is quite distinct from the mould, though probably not less injurious. The fertile threads are produced in dense clusters, each many times branched, and bearing elliptic acrospores obtuse at their apices, and of a violaceous tint (fig. 266). The oospores are beautifully reticulated and of a yellowish-brown colour (Plate X. fig. 212).