COMPOSITAE (COMPOSITE FAMILY) 457 
be continued late, as it is the plants that bloom and fruit after 
cultivation has ceased which are most certain to foul the soil. 
PERENNIAL RAGWEED 
Ambrosia psilostachya, DC. 
Native. Perennial. Propagates by seeds and by rootstocks. 
Time of bloom: June to September. 
Seed-time: July to October. 
Range: Illinois to the Northwest Territory, southward to Texas, 
Mexico, and California. 
Habitat: Rich prairie soil; invades all crops. 
> 
This is a much harder weed to combat than its annual relatives, 
for one must have a care in cultivation 
not to break up and spread abroad the 
creeping rootstocks and thus increase 
the plague. 
The plant looks very like the smaller 
Ragweed, but is stouter and grows two 
to six feet high. Leaves once or twice 
pinnatifid, with lobes usually acute, 
thick and bristly instead of thin and 
soft. Male flowers very abundant, 
on numerous long racemes, the invo- 
lucres deeply cup-shaped ; fertile flowers 
mostly solitary, the small, brown achene- 
like fruits obovoid, hairy, short-pointed, 
with fewer tubercles than the preceding 
species or sometimes none at all; they 
are often found in grass and clover 
seed and in baled hay. (Fig. 319.) 
Means of control 
Newly infested areas, if not so large 
as to make the method impracticable, 
should have prompt treatment with a 
strong herbicide — caustic soda or hot 
Fig. 319. — Perennial Rag- 
weed (Ambrosia psilostachya). 
x }. 
