178 COMMON WEEDS 



observed that Thistles are placed at the head of the list 

 as the worst weeds of grass land. 



As all the species of Thistles occur in grass land, it 

 will be convenient to refer to them here. 



The Spear Thistle (Cnicus lanceolatus Hoffm.) is a 

 large, strong, purple-flowered plant (Fig. 49), blooming 

 in July and August. The flower-heads are upwards of 

 an inch in diameter, either single or placed two or 

 three together, the whole plant being well provided 

 with short spines. Seeds are plentifully produced, and, 

 attached to the feathery pappus or down, are borne 

 away from the parent plant and distributed by the 

 wind. Percival says that the seeds "germinate very 

 easily in two or three days when they are placed in 

 suitable soil. The Spear Thistle, as met with in the 

 fields, is usually a biennial. I have, however, flowered 

 seedlings in one season, but such plants did not ripen 

 seeds satisfactorily, and were destroyed by frost in the 

 autumn." In the first year the Spear Thistle produces 

 a compact rosette of leaves, flowers and produces seed 

 in the second year, and then dies. The root system 

 is in the form of a deep tap-root. 



The Marsh Thistle (Cnicus palustris Hoffm.) is found 

 chiefly in damp, undrained pastures and meadows. It 

 is a biennial, and grows in a manner similar to the 

 Spear Thistle. The root system is much divided, the 

 stem branched, and the plant very spinous. The 

 leaves are hairy on both surfaces, the heads are three- 

 fourths of an inch in diameter in leafy clusters, the 

 flowers themselves being dark purple. The seeds, says 

 Percival, " only germinate under the peculiar acid con- 

 ditions of marshy, damp soil." 



The Stemless Thistle (Cnicus acaulis Hoffm.), some- 

 times termed the Chalk Thistle, is more troublesome 

 than is commonly recognised. It is a perennial which, 



