The Corn-Mildew (Puccinia graminis, Pers., Order Uredineae). — This disease of our grain crops and of many other grass plants is very widely distributed, like its hosts, over the earth, and is by far the most important to man of all mildews. Its life-history is passed in three generations —two of them on the grass plants and one on the barberry. In early spring the first generation is found on the dead leaves and leaf-sheaths of grass plants (in which the disease has hibernated), presenting to the naked eye the appearance of thin black streaks. When examined with a microscope these streaks are seen to consist of a great number of minute two-celled and thick-walled teleutospores (reproductive bodies), each situated at the end of a stalk (see A in fig. 2, vol. ix. p. 831). These have burst through the epidermis of the plant from their origin on threads among the tissues beneath. When they have been in contact with excessive moisture for a few hours, each of the spore-cells germinates by emitting a fine tube called a promycelium, on which there are borne small round thinwalled sporidia (reproductive bodies). The sporidia are easily detached and carried from place to place by the wind, and on alighting on the leaves of a barberry plant soon germinate by pushing out a small tube which perforates the epidermis and thus gains access to the interior of the leaf, where it branches copiously, and forms a mass of thread-like tissue called mycelium. The germ-tubes of sporidia are unable to enter the leaves, &c., of grass plants. In from six to ten days this mycelium gives rise to flaskshaped bodies called spermogonia (vol. ix. p. 831, fig. 2 B, sp), immediately under the surface of the leaf (usually the upper one), but breaking through it at the neck of the flask, out of which there protrudes a bunch of hairs. Within the flasks are formed at the end of stalks many exceedingly small oval bodies called spermatia, which escape through the neck. The function of these bodies has not yet been definitely made out, but that they bear a very striking resemblance to the male sexual organs of other fungi there can be no doubt. In the same leaves and on the same mycelium there arise several days later numerous basinshaped bodies containing erect stalks, bearing at the apex a number of round aecidiospores (reproductive bodies) in vertical series (vol. ix. p. 831, fig. 2 B, a). These constitute the second generation. On their escape they germinate by emitting a tube which, if the host on which they fall be a grass plant, enters the leaf through one of the stomata in the epidermis, and there by branching forms a new mycelium. On this there soon appears, bursting through the epidermis, a new generation consisting of round or oval uredospores produced at the end of stalks (vol. ix. p. 831, fig. 2 C). The uredospores constantly reproduce this generation, and in such abundance that the grain crops are extensively ravaged by its attack. It is in this generation that the term mildew is popularly given to the fungus. Later in autumn on the same mycelium the two-celled teleutospores appear, and these after hibernating renew in spring the life-history. This very remarkable cycle of generations was first traced by Professor de Bary.

The Hop-Mildew (Sphaerotheca Castagnei, Lev., Order Erysipheae') is a parasitic disease of the hop, though it is often to be found on many other plants, such as Potentüla, Spiraea, Epilobium, balsams, cucumbers, dandelions, plantains, &c. The thread-like mycelium appears on the young shoots and leaves of the hop in white spots, which gradually extend and finally unite. This mycelium bears many minute, round conceptacles (perithecia) which with their supporting threads are brown-coloured. Within each perithecium is found a somewhat oval body termed an ascus, containing eight ascospores (reproductive bodies).

The Vine-Mildew (Erysiphe Tuckeri, Berk., Order Erysipheae) is known only in one generation—called the oidiuιn stage. Soon after the flowering of the vine the attack takes place on the young leaves, from which the thin white mycelium spreads rapidly to the older leaves and twigs, which it does not appear to affect so injuriously. The chief damage is done to the grapes while they are in a very immature condition. The mycelium which travels over the surface sends down at intervals into the tissues short irregular protuberances called haustoria, which perform for it the functions of roots. Above these rise from the mycelium short stalks bearing each a single oval spore at the apex. The disease spreads on the same plant not only by the extension of the mycelium but by the scattering and germination of the spores. Here no perithecia are known.

The Paper-Mildew (Ascotricha chartarum, Berk., Order Erysipheae') grows on damp paper, and therefore is saprophytic in its mode of life. It consists at first of a branching filamentous mycelium on which minute globular spores occur. Finally a round brown perithecium is formed among the threads which appear as radiating from it. Within the perithecium are numerous linear asci containing each a row of dark elliptic ascospores.

For the Erysipheae generally see Fungus, vol. ix. p. 833.