# THE JOURNAL 



OF THE 



BOARD OF AGRICULTURE. 



During the last few years, whenever opportunity has offered, 

 I have been attracted to examine the structure and general 

 biology of the commoner weeds which trouble farmers, in 

 the hope that careful investigation would lead to some rational 

 system of dealing with these pests. Apart from its utilitarian 

 aspect, the study has proved of much scientific interest, to which, 

 however, there is no need to refer here. The present com- 

 munication deals with four of the commoner species of thistle 

 which arrest the farmer's attention both on arable land and 

 pasture. These are : (i) The Spear Thistle, (2) Tlie Welted 

 TJiistle, (3) The .Marsh Thistle , and (4) The Creeping Thistle. 

 The spear, marsh and creeping thistles have each hair of the 

 down or pappus which is attached to the " seed," branched 

 somewhat like a feather, while the hair of the down of the 

 welted thistle is simple. 



1. The Spear Thistle (Cnicus lanceolatus, Hoffm.) is the 

 strongest of the four plants mentioned, and grows usually 

 from 2 \ ft. to 4 ft. high (Fig. 1). Its root is a well-developed 

 tap-root, which descends from 9 in. to 1 ft. into the soil, 

 and bears few lateral roots. One or two very strong adventi- 

 tious roots are often produced near the surface of the ground 

 (Figs. 4 and 5). The upright stem is stiff, and the spines on the 

 edges of the leaves are long and stout. There are also short 

 stiff spines on the upper surface of the leaves, and long ones on 

 the bracts forming the involucre of the flower-head. The flower- 

 heads are erect and comparatively few, and are placed either 



Vol. XII. No. 12. 



MARCH, 1906. 



[NEW SERIES.] 



STUDIES OF WEEDS. 



I.— Some Common Thistles. 



L L L 



