PERENNIAL SOW THISTLE 45 



soil. The plant grows from two to five feet high and contains a 

 milky juice which can readily be seen by breaking the stem or the 

 leaf. As the leaves tend to turn one edge toward the sun, the plant 

 is sometimes called the compass plant. The plant begins flowering 

 in July and continues until frost. The yellow flowering heads are 

 borne on slender stalks. The seeds are ripe in the fall, are dark gray, 

 almost black in color, and resemble very closely those of the dark- 

 seeded varieties of the common lettuce. A tuft of hairs is. attached 

 at one end of the seed which aids in distribution. The seed of prickly 

 lettuce is very seldom found in commercial seed. 



Eradication. — Prickly lettuce causes very little trouble in well- 

 cultivated fields. Destroy stray plants with a hoe or spade, making 

 sure to get beneath the crown. Clean cultivation and full seeding in 

 waste places will occupy the land and keep out the weed. 



Perennial Sow Thistle ( Sonchus arvensis L.) 



Other common names. — Corn sow thistle, milk thistle, swine 

 thistle, tree sow thistle, field sow thistle, and creeping sow thistle. 



Description. — Perennial sow thistle is one of the worst weeds 

 in the State. It is, at the present time, more or less confined to the 

 northwestern part of the State but it is, however, rapidly working 

 southward. The plant is very common in waste places, along road- 

 sides, and in cultivated fields. It seems to thrive best in rich soil. 

 The plant flowers from June to August and matures seeds from July 

 to September. The plant ranges from two to four feet in height. 

 The stems are more or less hollow and are filled with a milky, bitter 

 juice which often gives it its name, milk thistle. There are two 

 other varieties of sow thistle quite common in the State. These are 

 annual varieties and are not considered bad weeds. These annual 

 sow thistles can readily be distinguished from the perennial by the 

 fact that they do not have the thick, creeping underground root stalks 

 which characterize the perennial sow thistle. 



The bright yellow flowers of the perennial sow thistle are clus- 

 tered together in a composite head which is from one to two inches 

 across. Many oblong, dark brown seeds are produced from each head. 

 Their surface is longitudinally ribbed and, when mature, they have 

 a dense tuft of hairs attached which aids in distribution as the wind 

 is thus enabled to carry them. In spite of the great number of seeds 

 produced, the most common mode of propagation is by underground 

 root stalks. The seed of the perennial sow thistle is very seldom found 



