The New International Encyclopædia/Oidium

OIDIUM, ō̇-id′i-ŭm (Neo-Lat., from Gk. ὠόν, ōon, egg). The conidial form of certain Erysipheæ, an important family of minute fungi growing on animal and vegetable substances. The species of Oidium consist of tiny tubular white or bright colored threads, forming flocks, simple or irregularly branched, assuming in their upper part the form of strings of beads, which finally break up into elliptic spores. Oidium albicans is found on the epithelium in the mouth and throat in the disease called aphthæ, or thrush. It is more common in children and aged persons than in those who are in the prime of life. Another species, Oidium Tuckeri, which has attracted great attention in Europe, is regarded by many as producing a destructive grape disease. It is the conidial form of Uncinula necator, or Uncinula spiralis. It makes its appearance at first in the form of a mycelium of creeping, branching filaments, which send out upright or decumbent jointed stems. Each bead-like joint of the stems develops into a sort of spore, numbers of which are finally discharged in little clouds. The grape disease was first observed in Kent, England, in the spring of 1845. The disease rapidly spread over other English vineries; was observed about the same time in the vineries of Paris, and soon in the vineyards of almost all parts of France, Italy, Greece, Tyrol, and Hungary, finally, and in a slighter degree, affecting the vineyards of the Rhine. Its ravages extended to Algeria, Syria, Asia Minor, and many other countries, among which is particularly to be noted the island of Madeira, where it proved almost completely destructive to the grapes and nearly put an end to the production of the celebrated Madeira wine. It is probable that the complete isolation of the Madeira vineyards made the progress of the disease more rapid, and its result more complete than elsewhere, by reason of the prevalence of the conditions favorable for it. This disease is more fully described under Grape as powdery mildew, for which remedies are there suggested.