~~ as 
fiers “7 
~ 
e 
‘ 
338 BULLETIN OF THE BUSSEY INSTITUTION. 
lettuce will put back the fungus so far that it does not recover for some © 
time. Ifthe disease has prevailed one season, the hot-heds of the next 
season should be made in some other locality, and if possible only seed 
from sound plants should be sown. As soon as the leaves mould they 
should be removed, and care should be taken not to throw them where 
they will be likely to get into heaps of manure which are to be used 
the next season. The common weed known as groundsel (Senecio 
vulgaris) should be removed with great care. It is found in hot-beds 
and all cultivated fields, and does more to spread the lettuce mould 
than the decayed lettuce leaves themselves, since in the groundsel, the 
odspores of Peronospora gangliformis are more abundant than in any 
other plant. 
