BACTERIAL DISEASE OF TOBACCO. 435 
PRELIMINARY INVHSTIGATIONS on 4 BACTHRIAL 
. DISEASE or TOBACCO. 
By G. P. DARNELL-SMITH, B.Sc., F.1.C. 
With Plate XXXVI. 
[Read before the Royal Society of N.S. Wales, November 6, 1918.] 
The incidence of Blue Mould.—*‘ Blue Mould”’ due to the 
fungus Peronospora hyoscyami has long been a serious 
disease of tobacco in Victoria, and during the last two 
seasons it has wrought great havoc in New South Wales. 
It makes its appearance particularly in seasons when the 
rainfall is excessive. As in the case of most fungus 
diseases, a particular relationship must exist between the 
weather, the plant attacked, and the fungus, before the 
latter can establish itself and spread with rapidity. ‘°‘ Blue 
Mould” especially attacks young plants in the seed beds; 
and when the particular relationship above referred to 
exists, it spreads so rapidly that if it makes its appearance 
the whole seed bed may be damaged in the course of a 
few days. 
The conditions in a tobacco seed bed are ideal for the 
spread of a fungus disease. The seed is sown broadcast, 
and the young plants come up in hundreds close together. 
The general practice is to pull the more sturdy plantlets as 
they mature and to plant them out in the fields. Under 
this method the seed bed is for a long time covered with 
young plants in close juxtaposition, so that a disease upon 
any one plant has every chance of spreading. Moreover, 
in the early stages, the seed bed is kept continually moist 
by watering, and the young plants are covered over with 
a layer of loosely scattered straw or dried grass to prevent 
them from scorching; the atmosphere surrounding them is 
