364 



OHIO EXPERIMENT STATION: BULLETIN 175. 



328 Tall Ragweed, Horseweed (A) Ambrosia bif- 

 ida L. This tall weed with its three-lobed leaves and 

 three=forked flower clusters finds its home in fertile bot- 

 toms and roadsides. The cut (Fig. 65) shows the 

 essential characters. 



Seeds, like those of the preceding-, but much larger, 

 five-eighths of an inch long, when enclosed in the dense, 

 pointed, five to seven horned, urn-shaped covering in 

 which these are usually found. Ohio roadsides may 

 certainly be freed from this weed. That can be done by 

 annual mowing before the plants flower. 



329 Western Ragweed (P) * Ambrosia psilostachya 

 DC. The name indicates the habitat of this as west of 

 us; it belongs in the country described by "Illinois and 

 westward." The weed resembles No. 327 but is 

 perennial by running roots; the seeds are also similar. 

 The plant is as yet local in Ohio. It may in time prove 

 as bad as any of the ragweeds. 

 Clotbur (A) Xanthinm Cana- 



dense Mill. Fig. 66 will show the characters of cockle- 

 bur, a weed much despised by shepherds and stockmen 

 generally. It is very common by roadsides and 

 occasionally infests moist fields; from both places it 

 may be removed by persistent pulling. The seeds are 

 enclosed in the large spiny burs, two in each bur. 



331 Smoothish Cocklebur (A) Xanthinm gla- 

 bratum (DC) Britton. This cocklebur differs from the 

 preceding in its rounder, slightly larger leaves and the 

 straight, smooth beaks of the bur; ranking with it as a 

 weed. 



332 Spiny Clotbur (A) *Xanthium spinosum L. 

 The spiny clotbur has been recieved from Hamilton, 

 Montgomery and Seneca counties and promises to 

 become widespread. It differs much from the preceding 

 in its white, hairy appearance and long, straw-colored, 

 three-forked spines, growing in the leaf axils. It is one 

 of the newly introduced weeds coming to us from tropical America. 



Figr. 65. Tall Ragrv.eed 

 {'After Milhpuugh.) 



330 Cocklebur, 



Fig. 66. Cocklebur. 

 {After Millspaugh.) 



THISTLE FAMILY, COMPOSITE. 



This is one of the most abundant families of plants in our flora and is 

 represented by a liberal supply of weeds; formerly the two preceding families 

 were included in it. It is named the composite family from the fact that many 

 single flowers are collected into dense heads, commonly known as the flower. 

 Many of the species have two sorts of flowers in the head. The border ones 

 having long, strap-shaped corollas, forming the rays of the head; they are 

 commonly white or yellow in color and are sometimes absent. The center of 

 the head has the disk flowers, which are inconspicuous and have tubular 

 corollas, often differing in color from those of the ray flowers. All have a 

 forked style and the anthers in a ring. We shall use the term '-rays" to 

 designate the flat, strap-shaped corollas of the border flowers, and the term 

 "disk flowers" to represent those of the center of the head. The old group with 

 milky juice and all the corollas strap-shaped is included in the chicory 

 family. The common term petals, as applied to daisies, asters and the like, is 

 too misleading to warrant its use in the descriptions of the list. 



