172 



Joiintdl of Agricitlture, Victoria. \ 10 Sept., 1918. 



fresh growth made by the vine subsequent to u spraying is quite un- 

 protected thereby, and liable to contamination. Vegetation is very 

 active in early spring, and a large quantity of unsprayed growth consti- 

 tutes a dangerous breeding ground, which may easily become a source of 

 bunch contamination in a wet season. Even the sprayed parts of the 

 vine soon lose a portion at least of their protective copper through the 

 action of rain, &c. A vineyard sprayed some days before infection can 

 take place is much less efficiently protected than one sprayed immedi- 

 ately before the dangerous moment. If sprayed too early, it may even 

 be necessary to repeat the treatment. Were it possible to exactly pre- 

 dict the day on which infection is to be expected, the best moment for 

 spraying would be the morning of that day. 



The first invasion of spring results from the germination of the 

 wintering spores (oospores) formed towards the close of the previous 

 season, and contained in leaf debris in the soil; neither Conidia (summer 



Fig. 4. 

 Macroconidia i^roduced in spting from 

 oospores contained in debris of infected 

 leaves. After Ravaz. (Highly magni- 

 fied.) 



Fig. 5. 



Macroconidia shortly aftertheirgermin- 

 ation — the Zoospores have nearly all been 

 expelled. The two zoospores in the centre 

 of the figure show the flagellse (taila), 

 which enable them to swim about in 

 water. After Ravaz. (Highly magnified). 

 Conidia (ordinary summer spores) ger- 

 minate in similar manner, but each one 

 only produces four to six zoospores. 



spores) nor Mycelium seem able to survive the winter. Oospore ger- 

 mination has been followed in the laboratory, notably by Eavaz in 

 France and Gregory in America. Earlier attempts were often unsuc- 

 cessful, owing to the specimens being insufficiently wetted during ger- 

 mination; they must, in fact, be bathed in water during the whole pro- 

 cess, the duration of which depends on the temperature. At 52 deg. F., 

 it lasts more than a day; at higher temperatures, a few hours are suffi- 

 cient. It follows that it is only warm, and at the same time very wet, 

 weather which would favour wholesale oospore germination, conditions 

 which are rare in early spring. 



Under suitable conditions of moisture and temperature, each oospore 

 emits one or two (rarely three) slender filaments, each bearing one large 



