224 MICRO-ORGANISMS AND FERMENTATION. 



principal axis end in short conical apices. The conidia are 

 oval, 12 to 30 /m. long, and have a smooth, colourless membrane. 

 In the conidia, as a rule, five or six swarming spores are formed, 

 which burst out when the conidia are immersed in water, and 

 penetrate through the epidermis of the leaves and fruit. The 

 growth forms thick, prominent whitish spots on both leaves 

 and fruit. In the interior of the plant, big, globular oospores 

 are formed (30 //. diameter), which have a brownish membrane, 

 smooth or slightly fluted, and are surrounded by the thin, 

 colourless, or yellowish, oogonium wall. This fungus causes 

 great injury, because the grapes either wither away or putrefy 

 according to the stage at w r hich they are attacked ; moreover, 

 it destroys the foliage. The species is indigenous to North 

 America, and was introduced into Europe in the year 1878 

 along with American vines ; it has now spread to all vine- 

 growing countries. Vine growers are endeavouring to suppress 

 this pernicious parasite by the application of copper sulphate 

 and calcium hydrate (Bordeaux mixture), and by similar 

 remedies. 



