436 G. P. DARNELL-SMITH. 
therefore continually damp. The conidiospores of Perono- 
spora hyoscyami are produced in countless numbers upon 
branched conidiophores upon the under side of the leaf only,. 
and to the naked eye the underside of the leaf appears to: 
be covered with a fluff of a faint violet tinge, This fluff is 
composed of conidiophores and spores. The spores germin- 
ate readily, and have not the appearance of spores capable 
of undergoing a long resting stage. While the production 
of oospores is Common among many members of the Perono- 
sporacee, the oospore of Peronospora hyoscyami is, accord - 
ing to Massee,”) unknown. I have not been able to find 
any trace of oospore formation in the specimens I have 
examined, but the intermittent manner in which the disease 
makes its appearance, renders it probable that oospores 
exist. In the allied genus Phytophthora infestans the 
oospore was only discovered by Clinton in 1910, though it 
had been sought for by mycologists since 1845. I have been 
unable to detect Peronospora hyoscyami upon Datura 
Stramonium or other weeds belonging to the Family Solan- 
aces, growing near tobacco beds upon which it might 
overwinter. 
Plants attacked by Peronospora hyoscyami early lose 
their bright green colour, and a practised eye can quickly 
detect the change. The point of development at which the 
*“blue mould’’ chiefly attacks the plants is in the seedling 
stage when they have from four to eight leaves; these have 
been previously figured. On older plants that have been 
transplanted to the field I have not often found the mould 
itself, though often they show spots and withering of the 
leaves; this lam inclined to attribute to a different cause. 
Tobacco culture in New South Wales is largely in the 
hands of Chinese; their seed beds are usually close to their 
planting-out grounds and adjacent to old seed-beds; it is 
not surprising therefore that the disease frequently re- 
