CANADA THISTLE, the creeping thistle (Cirsium arvense) of Europe, now extensively naturalized in North America, where it is found in fields and waste grounds from Newfoundland to British Columbia and southward to Virginia and California. In many places it is an exceedingly pernicious weed. It is a low per ennial, I ft. to 3 ft. high, creeping extensively by horizontal root stocks and forming patches. The smooth, grooved stems, some what branched above, bear deeply cut, exceedingly prickly leaves and numerous clustered, purple or white flower-heads about I in. broad. As the plant spreads by long, underground rootstocks as well as by innumerable wind borne seeds, it is very difficult to eradicate. Intensive cultivation of field crops and rigorous cut ting of the plant along roadsides and in waste grounds before the seeds mature are the most effective means of control. (See THISTLE.)