The under surface of the leaves of the white Dutch clover are often sprinkled with black spots, which are nearly round and very numerous. These are so many clusters of fungi belonging to a different section, in which the threads are the important feature. But another parasite is also found on leaves of the same plant, in which the pustules are far less numerous and regular, and are often found on the petiole as well as the leaf, distorting them and twisting them in various directions Plate VII. fig. 154). This is the clover rust (_Uromyces apiculata_, Lev.), which is a parasite on numerous plants, being found also on the great water-dock and other kinds of dock. The spores are ovoid and brown, with a short peduncle (Plate VII. fig. 155). A very beautiful species occurs on the leaves of the ladies-mantle (_Alchemilla_), but hitherto we have not been fortunate enough to collect it. It can scarcely be too great an assumption to suppose that every one is acquainted with the goat-willow (_Salix caprea_), or that every schoolboy knows the birch (_Betula alba_). It may be proceeding a step too far to affirm that all who know these trees well enough to distinguish the one from the other, will have observed the under surfaces of the leaves of both sprinkled with a golden dust, during the summer months, and which are the spores of a parasitic fungus. So common is this orange-coloured powder on leaves of the trees above-named, that we can hardly believe any one to have had a branch of either in his hand and not observed it, provided any leaves adorned the branch in question. What this parasite is, and what its associates, it is our province to endeavour to explain. Our figure (Plate VIII. fig. 160) represents a leaf of the sallow or goat-willow, with the under surface exhibiting yellow patches, consisting of spores, which are magnified in the next figure (Plate VIII. fig. 161). This exceedingly common rust is termed _Lecythea caprearum_, Lev., when in the condition figured; but in reality this is only the summer stage, bearing the summer fruit of _Melampsora salicina_, which latter attains its mature development on the same leaves in the succeeding winter (Plate IX. fig. 191) or early spring. Of course this latter remark applies to the fallen leaves, for at this period all the willows and other deciduous trees are bare. But the leaves, before they fall, give evidence of the parasite at work; and if the collected decaying mass of rubbish at the base of sallow bushes be examined about March, these leaves will be found bearing upon them mature heaps of elongated, wedge-shaped spores, closely packed side by side (Plate IX. fig. 192), and which, whilst still adherent, may often be found in active germination, as represented in an allied species at the bottom of our plate (Plate IX. fig. 197). This phenomenon consists in the production of cylindrical tubes, more or less elongated, from the upper extremity (rarely from the base) of the prismatic spores. These