396 



Journal of Agriculture , Victoria. [lo June, 191 i. 



The absence of this form in France lerl mycologists to consider French 

 Oidium to be a different fungus to that known in America. It was subse- 

 quently found that they were one and the same organism, and that the for- 

 mation of its winter fructifications is a r|uestion of climatic co!iditions.* 

 Such conditions are more fre(]uent in Amt-rira than in France. 



The formation of perithecia has a practical interest, since it is thought, 

 in some quarters, that the fungus resulting from the germination of spores 

 contained in the.se bodies pos.sesses greater vigour, and is therefore capable 

 of doing more damage than that resulting from hibernating forms. So far 

 as the writer is aware. ]ierithecia of Oidium has not vet been observed 

 in Victoria. 



The discovery of the.se bodies in Franre in 1893 proved the identity 

 of French and American Oidium and the American origin of the fungus. 

 It made its first appearance in France in 1845, or long before the other 

 vine fungi of American origin we shall shortlv consider. For the first 

 few years, in fact, until a remedv was found in the shape of sulphur, its 

 ravages were very considerable. Nowadavs the damage caused bv it is 

 much less serious than that due to Downv Mildew. 



OIDIUM {U ucinula spiralis) 



I. Horizontal mycelium with suckers (black) and upright spore-bearing filaments. 

 [after Durand). 2. The same more highly magnified (after Vialta). 3. Perithecium 

 or receptacles containing the winter spores [after Vialla). 



The diagrams reproduced illustrate the ditferent forms of the fungus. 

 It differs radically from all other vine fungi in that the mycelium- or 

 vegetative portion is exterior to the tissues of the plant. It runs over the 

 surface, sending suckers into the cells by means of which it obtains its 

 food. From this mycelium, spore-bearing filaments arise on which Conidia 

 or summer spores, serving to spread the disease, are produced in great 

 numbers. This external character of its mycelium makes the Oidium more 

 amenable to treatment than almost any other vine fungus. When, as is the 

 case with the other species which attack the vine, the vegetative portion is 

 buried in the tissues of the plant, it is out of the reach of fungicide treat- 

 ment, since the tissues are more easily damaged by chemical agents than 

 the mycelium of the fungus. In sui'h cases, preventive treatment alone 

 can be successful. With Oidium, on the other hand, direct or curative 

 action is easy, since an application of sulphur destrovs the growing portion. 



* If, after a period of warm, moist weather, whit^h has pnxhu-ed .an ahiindant jf row th of Myre'iiini, the 

 temperature .surldeiilv fails to near the Invest 'i'nit for 'he t^rowth of the fun^ais (:iO°K. ), they are 

 ))rodiiced rapidly and in j,'-reat numbers.- - I'rof. F. T. Bioletti, Hulk'tin No. 186, University of California 

 Publications, p. 325 



