in autumn has been found very useful in killing Thistles and Perennial Sow- 

 thistle in Manitoba. This would also be good practice in Eastern Canada, 

 and the land might afterwards be thoroughly worked down and ridged up 

 with a double mould-board plough for the winter. 



The chief safeguard of farmers against Canada Thistle and all similar 

 deep-rooted perennials is undoubtedly a regular short rotation of crops such 

 as is described on page 11, as practised here at Ottawa by Mr. Grisdale. As 

 an evidence of the above, it may be noted that the Canada Thistle is seldom 

 seen in the crop on farms given to alternate husbandry, and it is everywhere 

 more of a wayside weed which spreads on to farms when these are not pro- 

 perly worked. 



A curious variety of the Canada Thistle in which the leaves are flat, 

 almost entire and spinose only on the margins (Cnicus arvensis, Hoffm., 

 var. setosus, Ledeb.), has been sent from Manitoba. This variety, however, 

 has not proved stable, for plants grown from seeds of the variety can hardly 

 be distinguished from the ordinary prickly form. 



In addition to the Canada Thistle, two other species are sometimes com- 

 plained of by farmers. The PRAIRIE THISTLE or WESTERN BULL THISTLE, 

 Cnicus undulatus , Gray, is a native perennial with running rootstocks and 

 large whiter-woolly leaves and stems; flower heads large, nearly 2 inches 

 across, solitary at the end of the branches. This is not a very serious pest 

 and soon disappears when the land is put under crop. 



The BULL THISTLE or SPEAR THISTLE, Cnicus lanceolatus, Huffm., is a 

 large coarse biennial, introduced from Europe, 2 to 4 feet high, widely 

 branching, with many large deep-purple flower heads 1J inches high by as 

 much across. This plant is very abundant in many parts of Canada, and 



Sarticularly so in the partially cleared districts in British Columbia. As 

 md is cleared and worked regularly, this weed, each plant of which lives 

 only for two years, is killed out. 



60 



