THE SUNFLOWER FAMILY 153 



harvest, or, if seeded, the autumn growth should be closely 

 cut with a mowing machine within two weeks after the grain 

 crop is cut. Hoed crops require attention with the hoe occasion- 

 ally after general cultivation is discontinued. Lands badly 

 infested should be put under a three-year rotation of crops, 

 with prompt and thorough cultivation or mowing in early autumn 

 after the crop has been removed. 



ALLIED SPECIES: Perennial Ragweed {Ambrosia psilost- 

 achya DC.) is a western plant found on the prairies, resembling 

 Common Ragweed in the shape of the leaves and flowers 

 but with running perennial rootstocks, which throw up at inter- 

 vals weak stems, 1 to 2 feet high. Leaves finely downy. The 

 seed closely resembles that of the above, but as a rule is more 

 regularly oval. 



This ragweed is seldom troublesome in Canada, either on 

 farms or from the presence of the seeds among crop seeds. With 

 the more extensive cultivation of grasses and alfalfa for seed 

 in the West, it will require more attention. 



Cockleburs or Clotburs (Xanthivm) are tall, coarse, 

 much-branched annuals. The leaves are heart-shaped or ovate, 

 except in Spring Clotbur (Xanthiuvi spinosum L.), which 

 has lance-shaped or ovate-lance-shaped leaves, tapering at 

 both ends. As in the ragweeds, spikes of male flowers are borne 

 above with numerous clusters of female flowers below them. 



The 2-celled "fruits," commonly called "burs," are from 

 1 to 1^ inches long, hard and leathery, armed with beaks (except 

 in Spring Clotbur) and covered with more or less long, thick, 

 hairy, recurved and crowded prickles. Each bur contains 2 

 oblong, flat seeds which retain their vitality for several years. 



Some species are abundant as weeds in river bottoms and 

 moist soils throughout the Prairie Provinces, and are particularly 

 troublesome to stockmen in parts of Alberta. Other species 

 are plentiful in the eastern provinces and are frequently reported 

 as a nuisance in sheep pastures. 



These coarse, annual weeds should be destroyed by hand- 

 pulling, continued from year to year. 



