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, Fic. 356.— Creeping or Canada 
needle-like spines pointing in all — TPstle (Céretum arvense). x 2. 
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. dicecious, 
the pedicels and bracts without spines, the florets rose-purple, 
fragrant. Achenes oblong, smooth, with fine, white pappus. 
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 
