COMPOSITAE (COMPOSITE FAMILY) 



515 



prickle to such attempts at its extermination. The laws are very 

 good but enforcement is neglected. (Fig. 356.) 



The jointed, horizontal rootstocks are the most obnoxious part 

 of the plant ; round, slender, like 

 tough, white whipcords, lying so 

 deep in the ground as to be al- 

 ways sure of moisture, they creep 

 in every direction for rods even 

 (the writer helped to trace one 

 over eighteen feet long), sending 

 up new plants at short intervals ; 

 if broken and dragged about by 

 farm implements, the pieces grow, 

 so that ordinary cultivation but 

 serves to spread the pest. Stem 

 one to four feet tall, erect, slen- 

 der, grooved, woody, nearly 

 smooth. Leaves three to six 

 inches long, sessile and slightly 

 clasping, deeply and irregularly 

 pinnatifid, the margins loosely 

 crisped, toothed with hard, white, 

 needle-like spines pointing in all 

 directions. Heads in terminal and axillary clusters, the topmost 

 ones opening first, the bloom proceeding in succession down the 

 stalk. The heads are about a half-inch broad, imperfectly dioecious, 

 the pedicels and bracts without spines, the florets rose-purple, 

 fragrant. Achenes oblong, smooth, with fine, white pappus. 



FIG. 356. Creeping or Canada 

 Thistle (Circium arvense). X i. 



Means of control 



Persistent starvation of the rootstocks by keeping them de- 

 prived of the food-assimilating green leaves ; this means frequent 

 cutting throughout the growing season for at least two years. In 

 cultivated ground the required tillage keeps the weed in check. 

 In grain fields a spray of Copper sulfate in a solution of fifteen 

 pounds to a barrel of water (fifty-two gallons), applied before the 

 grain begins to head and when the young thistles are not more 



