THE WEEDS OF CULTIVATION 



77 



portions as there are seeds, and it dehisces transversely ; that of 

 the Pansy also opens to let out its seeds, and splits at the midrib 

 into three valves, each containing a row of seeds, which are forced 

 out several feet by the walls of the valve coming together as the 

 fruit gets dry. The Shepherd's Needle is in some respects unlike 

 most of the Umbelliferse. It is sometimes called Venus' Comb, 

 from the shape of the fruit, which is nearly two inches long 

 and resembles a comb, the edges being 

 fringed with teeth. 



FIG. 32. Shepherd's Needle (Scandix 

 Pecteri). 



FIG. 33. Black Medick 

 (Medicago lupulind). 



In discussing the weeds of arable land it is almost impossible 

 to say which weeds are associated with any particular crop, for 

 at the present time there is a regular rotation of some three or 

 four crops on all cultivated land. At Rothamsted Experimental 

 Station, however, a certain field has been grown continuously in 

 wheat for more than fifty years, and the weeds that havegiven most 

 trouble on the unmanured plots are the Black Bent Grass (Alo- 

 pecurus agrestis] and the Black Medick. Of those two, the Bent 

 Grass is by far the greater pest ; the Black Medick, indeed, is of 



