234 



WEEDS OF THE FARM AND GARDEN 



flowers with tubular corolla. Common especially in the 

 saline soils from Nebraska to the Dakotas, British 

 Columbia, California and New Mexico. 



Smaller Ragweed (Ambrosia artemisiae folia, L.). A 

 branched, hairy annual, growing from one to three feet 



high, with thin, once to twice- 

 pinnatifid leaves, the upper, al- 

 ternate, the lower usually 

 opposite, pale or canescent be- 

 neath ; flowers monoecious, the 

 staminate above, the pistillate 

 in the lower axils of the leaves; 

 fertile heads globose or obo- 

 void, short beaked, four to six- 

 spined. A troublesome weed 

 in all parts of the state and 

 very generally distributed 

 throughout the United States. 

 Greater Ragweed (Ambrosia 

 trifida, L.). A stout, rough or 

 sometimes nearly smooth an- 

 nual, three to twelve feet high ; 

 leaves opposite, petioled, three- 

 nerved, deeply three-lobed, the 

 lobes being ovate-lanceolate 

 and serrate, the upper leaf 

 sometimes ovate and undi- 

 vided ; flowers monoecious, the staminate borne on spikes 

 surrounded by large bractlike leaves ; involucre inclosing 

 a single oily, beaked seed, five to seven-ribbed, each rib 

 bearing a tubercle near the summit. Ragweeds produce 

 a large number of seeds, and though the weeds are easily 

 destroyed, the seeds retain their vitality and are readily 

 carried from place to place by drifting snow. 



Western Ragweed (Ambrosia psilostachya, D. C.). 

 This perennial ragweed much resembles hogweed, but 



Fig. 147. Marsh elder or 

 half-breed weed (I<va xanthi- 

 folia). (Theo. Holm.) 



