WEEDS 



173 



Prickly lettuce (Lactuca scariola). Although the intro- 

 duction of this plant into America occurred but recently, it 

 has already spread so extensively as to become a common 

 weed. It may be known by its erect prickly stems and bluish- 

 green leaves, most of which are turned edgewise and point 

 north and south. It is frequently a winter annual and is re- 

 garded by botanists as being the parent of our garden lettuce. 



Ragweed (Ambrosia 

 artemisicefolicf). Rag- 

 weed, a homely plant 

 with much-dissected 

 leaves, is found al- 

 most everywhere in 

 cultivated land. At 

 flowering time the in- 

 significant greenish- 

 yellow flowers shed 

 great quantities of yel- 

 low, dustlike pollen, 

 which collects upon the 

 shoes and clothing of 

 all who pass through it. 

 The pollen is regarded 

 with good reason as be- 

 ing one of the causes 



FIG. 122. Ragweed, a common weed regarded 



oi nay lever. as ^j ie cause O f i ia y fever 



Wild mustard (Bras- 



sica arvemis*). Several species of mustard are known under 

 the general name of wild mustard, but the species named above 

 is the most widespread and troublesome. The mustards may 

 be distinguished by their coarse hairy leaves, clusters of bright 

 yellow flowers, and long spikes of seed pods. They spring up 

 quickly, grow rapidly, and soon smother less strenuous plants. 

 The turnip is a closely related species of Brassica. 



Photograph from American Steel and Wire Co. 



