_Mal nero_ of the Vine is a particular case of black spotting and streaking of the leaves for which no satisfactory explanation is as yet to hand. As with Chestnuts, Walnuts, and other plants containing much tannin, the dark spots appear to be due to this substance, but whether the predisposing cause is a lack of some ingredients in the soil, or some temperature reaction, or fungi at the roots, is as yet unknown. The most recent explanation puts the disease down to the action of bacteria, but the results obtained by different workers lead to uncertainty. The "dying back" of leaves, especially of grasses, from the tip, is usually accompanied by a succession of colours--yellow, red, brown, to black--and is a common symptom of parching from summer drought; and spots of similar colours, frequently commencing at the margins of leaves, are characteristic symptoms of the injurious action of acid gases in the air. Brown and blackish spots on Pears are caused by a species of _Thrips_. In many cases the minute spots of Rust-fungi on one and the same leaf are bright orange yellow (_uredo_), deep brown, or almost purple-black (_teleutospores_), foxy-red brown (older uredospores), or dead slaty black where the old teleutospores have died off--_e.g._ _Uromyces Fabae_ on Beans, _U. Pisi_ on Peas, etc. _Parti-coloured leaves._--The leaves sometimes start shrivelling with red edges, while yellow, red, and finally brown and black blotches appear on the lamina, from no known cause--_e.g._ Vines. In other cases similar mimicry of the autumnal colouring of leaves results from the action of acid gases. _Burning_ is a common name for all cases where the leaves turn red or red-brown in hot, dry weather, and many varieties are distinguished in different countries and on different plants, because species react dissimilarly. The primary cause is usually want of water--drought. _Foxy leaves_ are a common sign of drought on hot soils, and the disease may usually be recognised by the gradual extension of the drying and fox-red colour proceeding from the older to the younger leaves, and from base to apex--_e.g._ Hops. _Coppery leaves._--The leaves of the Hop, etc., may show yellow spots and gradually turn red-brown--copper-coloured--as they dry; the damage is due to _Tetranychus_, the so-called Red Spider. These cases must of course be carefully distinguished from the normal copper-brown of certain varieties of Beech, Beet, _Coleus_, etc. _Silver-leaf._--The leaves of Plum, Apple, and other fruit trees often obtain a peculiar silvery appearance in hot summers, the cause of which is unknown. Discolorations in the form of confluent yellow and orange patches, etc., resembling variegations, are not infrequently due to the ravages of Red Spider and mites--_e.g._ on Kidney Beans.