Mildew

Mildew, the name popularly applied to various fungi, either parasitic upon higher plants or saprophytic upon damp paper, linen, etc. The chief are the vine-mildeiv and the corn-mildew - the former, Erysiphe (formerly Oidium) Tuckeri, consisting of a white "mycelium," or "spawn" of fine threads covering the leaves and young fruit, sending suckers, or "haustoria," into the plant, and bearing also ascending stalks, each ending in an oval "spore" (.q.v.). Corn-mildew (Puccinia graminis), belonging to a distinct order of Fungi, the AEcidiomycetes, is a remarkable example of "heteroecism," living, that is, parasitically on more than one host plant. On straw or dry grasses in autumn it appears as narrow black lines, which under the microscope are seen to consist of a mass of two-celled spores, each terminating a hypha or thread of spawn. In spring each of these tclcutospores (" last spores"), as they are called, puts out a short tube or thread, termed the promycelium, bearing on its branches several minute cells or sporidia. These will only germinate on the leaves of the barberry, which they pierce and fill with mycelium ("spawn"). This mycelium bears flask-shaped bodies called spermoyones on the upper surface of the barberry leaf, which are filled with small oval bodies, called spermatia, of unknown f unction.but possibly male. Through the under surface of the barberry leaf there burst from the same mycelium numerous round orange-coloured bodies which spread into small cups, known as cluster-cups and filled with chains of spores. These cluster-cups were formerly known as AEcidvani berberidis, and their spores are termed cecidiospores. These spores will only germinate on the leaves of some grasses, filling them with mycelium and bursting through their surfaces in a mass of oval, brown, one-celled spores known as Uredospores, formerly considered a distinct fungus, Uredo seyetum. These spores can infect other grasses, giving rise on them to mycelium bearing similar spores; but late in summer, among the uredo-spores and on the same mycelium, appear the black, two-celled resting-spores or teleutospores, already described, which live through the winter and start the fresh cycle of generations.