764 



MANUAL OF POISONOUS PLANTS 



Distribution. In alluvial ground or along streams, Saskatchewan and 

 Nebraska to New Mexico, Utah and Idaho. In the western part of the state 

 of Iowa this weed is extremely common as in Woodbury, Harrison, Monona 

 and Fremont counties. It occupies not only the vacant lots but is found in 

 the streets and cornfields. To the west in Nebraska it becomes increasingly 

 abundant and in the irrigated fields of portions of Colorado it is frequently 

 8 feet high. It is common in the Red River Valley of the North and other 

 parts of Minnesota and Dakota, and Manitoba. It is a most aggressive weed. 



Poisonous properties. This plant and the preceding produce an unusually 

 large amount of pollen and have been looked upon as in part responsible for 

 hay fever, the pollen being simply an irritant of the nasal mucous membrane. 



Fig. 441. False ragweed (/I'a xanthifolia). 

 Tlie pollen is possibly a cause of hay fever. (Dew- 

 ey, U. S. Dept. Agr.). 



6. Ambrosia (Tourn.) L. Ragweed 

 Herbs; leaves alternate or opposite, lobed or dissected; flowers in heads, 

 fertile, 1-3 together, sessile in the axils of leaves or bracts; involucre of the 

 pistillate flowers top-shaped, ovoid or globose, closed, l-flowered, armed with 

 4-8 tubercles or spines; corolla none; pappus none; involucre of the staminate 

 flowers saucer-shaped, 5-12 lobed, many flowered; receptacle nearly flat or with 



