94 THE RAISIN INDUSTRY. 



rubbed smooth, especially on the green stems or berries, we see below 

 them, in the epidermis of the vine, the mycelium or stem of the fungus 

 spreading in all directions from a central point, like the roots of a tree 

 or plant. This part of the mildew corresponds with the stem and root 

 of a plant, while the upper, powdery part is the one which produces 

 the spores or the seed, conidia and peritheca, all of which are repro- 

 ductive organs. The grapes thus attacked gradually dry up or crack 

 open. The leaves are eaten through and dry up, and the whole plant 

 becomes badly diseased, and may even die. 



Powdery Mildew (Oidium Form), Greatly Magnified. 



History and Distribution. The powdery mildew or Oidium was 

 observed for the first time in the year 1845 in hothouses in England. It 

 immediately began to spread, and in a few years infested all the vine 

 districts of the Old World. Before any remedy had been discovered, 

 many vine districts were so injured that they have not since been able 

 to recover. Thus in 1850 and 1851 France suffered greatly from this 

 mildew, and the Island of Madeira, which for three hundred years had 

 produced the finest wines, had its grapevines so injured that they up to 

 this time have not again produced as good a quality of grapes as before 

 the advent of the disease. The Grecian Islands as well as Morea were 

 also visited by the powdery mildew, and though the latter is now kept 

 in control, the general opinion is that the quality of the currants is 

 not as high as it was before the mildew appeared. Now there is 

 probably no place in the Old World where grapes are not attacked by 

 this mildew, although some places are injured much more than others. 

 Adjoining vineyards are often differently attacked, some being even 

 entirely free, while others are visited yearly. Young vines are less 

 attacked than old ones, and in favorable, places the mildew seldom 

 infests vines before they are two or three years old. Elevated places 

 and localities exposed to winds and cold are generally attacked by the 

 first stages of this oidium, while its second or last stage prefers low, 

 damp places exposed to dew or fog. 



The American form of the powdery mildew or Undnula spiralis differs 

 in some respects from the European Oidium, not as to its effects, but 

 as to its microscopical characteristics. The Oidium occurs in Europe 

 only with certain generative organs called gonidia, while the American 



