A SEED KEY TO COMMON WEEDS 351 



brown. S., oblong, four-angled in cross section; contracted at 

 the base to a sharp point; rather thickly dotted with particles 

 of resin-like matter. 0., common in lowlands. Native. 



82. Eupatorium perfoliatum L. Thorough wort, Boneset. L., 

 1.8 — 2.8 mm. W., .2 — .5. C, dark grayish brown with irri- 

 descent spots. S., oblong, four-angled; contracted at the base 

 into a rather long drawn out point. 0., common in waste land. 

 Native. • 



83. Erigeron annuus (L.) Pers. Daisy Fleabane, Sweet 

 Scabious. L., .6 — 1. mm. W., .1 — .4 mm. Color and shape 

 as in the following species but slightly darker and with the 

 hairs less evident. 0., quite a bad weed. Introduced from 

 Europe. 



84. Erigeron canadensis L. Horseweed, Butterweed. L., 

 .8 — 1.5 mm. W., .2 — .6 mm. C, yellowish white. S., flattened; 

 somewhat oval and broader at the apical end ; covered with stiff 

 v.hite hairs. 0., common in alfalfa and along hedge-rows. 

 Native. 



85. Inula Helcnium L. Elecampane. L., 3.8 — 4.8 mm. "W., 

 .8 — 1.2 mm. C, light or dark brown. S., linear, four-angled 

 with about twenty to thirty fine longitudinal lines; base of the 

 pappus bristles quite persistent. 0., common in rocky pastures 

 and by roads. Introduced from Europe. 



86. Ambrosia trifida L. Giant or C4reat Ragweed. L., 9 — 

 12 mm. W., 4 — 8 mm. C, dark brown to black. S., thick 

 spindle-shaped or somewhat turbinate with five to seven very 

 prominent ribs terminating in points slightly above the middle 

 of the seed ; beak 2 — 3 mm. long and quite thick at the base. 

 0.> common in low lands. Native. 



87. Ambrosia art emisii folia L. Ragweed, Roman Wormwood, 

 Hogweed, Bitterweed. L., 2.4 — 4.8 mm. W., 1.1 — 1.5 mm. C, 

 dark mottled brown. S.. very thick spindle-shaped with from 

 five to ten lateral ridses terminating in short beaks just above 

 the middle; terminal beak about 1.5 mm. long. 0., common in 

 dry meadows and found in alfalfa, red clover and cereals. 

 Native. 



88. Xanthium canadensis Mill. Cocklebur, Clotbur. L., 

 Fruit about 18 to 25 mm. long. W., about 10 mm. C, rusty 

 brown. S., thick spindle-shaped terminating in two stout beaks 



