Mildew. 



151 



Fig. 43, enlarged 200 diameters. Each of the transparent or pale whitish-grey egg- 

 like bodies seen in the illustration is a reproductive body or spore, which answers the 

 purpose of a seed, for the spores germinate readily (even whilst still attached in club 

 form) and reproduce the mildew. Germinating spores are 'shown at the top of the 

 illustration, and the whitish mass of woven spawn from which the clubs arise is seen 

 at the bottom. This condition of Rose mildew is known to botanists at its early stage 

 under the name of Oidium leucoconium. 



The fungus of Rose mildew is preserved through the winter in a remarkable 

 manner. Late in the autumn, at the time when Roses are shedding their leaves, the 

 mildew fungus produces upon the leaves from its thin bed of whitish spawn a remark- 

 able growth similar with A in Fig. 44, enlarged 200 diameters. This is really the 



perfect state of the fungus of Rose mildew known as 

 Sphaerotheca pannosa. When the fungus is in this condi- 

 tion it consists of innumerable microscopic brown globular 

 cases ; each case is isolated and furnished with numerous 

 radiating arms or tentacles as illustrated. If one of these 

 microscopic globes is cut in two it is seen to contain a 

 second minute globular bladder inside, and within each 

 inner bladder eight spores of the fungus are neatly packed, 

 as seen at B. 



The spores of the fungus (invariably eight in a case) 

 are preserved through the winter in the two microscopic 

 globes, one within the other, as just described. The 

 enclosing cases are frost proof and wet proof, but when 

 the spring returns the outer case opens, and sets the inner 

 case free ; the inner case or bladder then sails about in 

 the air, where it soon opens and sets the spores free in the atmosphere. Such of 

 these spores as alight upon Roses immediately germinate and produce the early 

 or Oidium condition of Rose mildew. 



If Rose mildew only grew upon garden Roses there might be some chance of its 

 extermination, but it unfortunately grows on the wild Roses of our hedge-rows as 

 well as upon the Meadow Sweet and other wild rosaceous plants. Rose gardens are 

 therefore often infected from the nearest hedge-side. 



One of the most approved remedies for Rose mildew is one oz. of soft soap to 

 one gallon of water, and one handful of flowers of sulphur stirred into each four 

 gallons ; the mixture to be used with the syringe. Pure water to be afterwards used 

 with the syringe. Sulphur dusted on the leaves when wet is the remedy usually 



f 



Fig. 43.' ROSE MiLutw. 



Early stage Oidium leucoconium 



Enlarged 200 diameters. 



* For the drawings and notes of Figs. 43, 44, 45, and 46, I am indebted to the courtesy of my friend 

 Worthington G. Smith, Esq., F.L.S. 



