WEEDS 339 
readily transported seeds, such as goldenrod, thistles, prickly 
lettuce, and milkweeds, to seed all adjoining parts of the farm. 
Many useful plants and still more harmful ones spread by 
vegetative means so as to overrun neighboring ground. In 
this way a blackberry patch may spread by the root so as to 
become a nuisance, and black raspberry bushes will travel by 
means of their long root- 
ing branches (fig. 72) so 
as to cover much ground. 
Couch grass, or quack 
grass (fig. 245), growing 
beside a cultivated field 
or garden will soon spread 
into the cultivated soil 
by means of its vigorous 
rootstocks. 
Methods of destroying 
weeds cannot be treated 
in detail in a textbook 
on. botany, though a few 
words may be given to 
the subject. Weeds which 
have gone to seed should 
not be plowed or spaded Fic, 246. Wild oats, a grass belonging to 
under, but should be the same genus as the cultivated oat 
burned when dry. Tt will It is an extremely troublesome weed, espe- 
be found well worth while cially in fields of the small grains. After 
“Farm Weeds of Canada ” 
to rake away from fences 
and burn all accumulations of tumbleweeds. Wild mustard, 
which is a very troublesome weed in fields of the small grains, 
is readily killed by spraying with a solution of copper sulphate 
or iron sulphate. Weedy lawns are sometimes improved by 
very careful salting, which does not injure the grass. Gravel 
walks may be cleared of weeds by watering them with a highly 
poisonous solution of sodium arsenate or of crude carbolic acid. 
Rotation of crops (that is, following the crop of one year by a 
