These fungi are of various species, and specimens are given here in Plate xxii.: on the leaves they form usually a hard, thin, black coat; while on the twigs and stem they are of a looser texture, forming masses of minute erect threads. They are not confined to New Zealand, and most writers on Coccididæ in Europe and elsewhere mention them, though only casually. They are, in fact, apparently, only the usual growths appearing on any decomposing substance, such as the honeydew is. Gardeners and tree-growers ought to clearly understand that the appearance on their plants of this black sooty covering is almost always an indication of the presence of some Homopterous insects. In New Zealand, on account of the greater prevalence of Coccididæ, the insects will most probably be Coccids; but by no means necessarily so, for many Aphididæ, Psyllidæ, and Aleurodidæ produce the same effects. This is by no means as well understood as it should be, either by gardeners themselves or by those who write on trees and planting. The fungus growth is usually imagined to be in itself a disease of the plant, and efforts are made for its treatment without regard to its real origin, the insects on the leaves or bark. Under the names of "smut," "black blight," &c., it is often referred to as a destructive pest; and remedies are suggested which can, of course, have no permanent effect unless they are equally efficacious against the insect producing the honeydew. It is probably from this cause that sulphur, which is an excellent remedy against fungus, has been so great a favourite with those who pretend to have discovered what are called "scaly-blight destroyers;" and gardeners, seeing, perhaps, these nostrums clean some of the fungus from their trees, are under the false impression that the "scale" is also cleared away. The truth is, that the real remedy against "black blight" is to kill the insects on whose excreta it flourishes, if that can be done. As to the modes of doing this see Chapter V. It is not, of course, pretended here that fungi of different kinds, and even those specially referred to, will not grow independently of insects and honeydew; and trees are, undoubtedly, subject to fungoid diseases which are not to be traced to any animal action. Still, the rule holds good; and the first effort of a gardener on the appearance of black blight on his plants should be to discover the insects on its leaves or bark, and deal directly with them. Once they are destroyed the fungus growth will in a short time disappear. CHAPTER IV. CHECKS TO INCREASE OF COCCIDIDÆ, PARASITES, ETC.