73 III. INTRODUCED SPECIES. 



same spot. Trifolium elegans and Barkhausia setosa are 

 plants whicli have latterly become included in the lists of 

 aliens occasionally found wild in England ; seen one year 

 in one i)lace, another j^ear in another place ; but nowhere 

 permanent, or reapj)eariug on the same ground for a 

 series of years. Apparently their seeds are imported 

 afresh, and are sown intermingled with seeds of the com- 

 mon clover. — Lolkim temulentum and Bromiis secalinus 

 have been longer known in our corn fields, and are much 

 more frequently met with. But even these grasses 

 scarcely keej) constant hold of the ground ; rather ap- 

 pearing to be re-sown by human hands, along with the 

 seeds of rye or other kinds of corn among which they 

 grow. They thus occvqyj a position somewhat interme- 

 diate between the aliens and colonists. — Agrostemma Gi- 

 thago and Centaurea Cyanus are more frequent, and also 

 more persistent in the same fields, than the Lolium and 

 Bromus before named. Apparently they sow and scatter 

 their own seeds ; and thus they may be said to hold their 

 ground without the aid of man, except in so far as his 

 regular preparation of the ground may be requisite for 

 their growth and permanence on it. — Papaver duhium and 

 Chrysanthemum segetum are highly abundant, and now 

 constantly perpetuate themselves by seeds in cultivated 

 ground ; occasionally also growing on cliffs by the sea, 

 on rubbish heaps, and about quarries. Still, it is at best 

 uncertain, whether even these seemingly well-established 

 species could keep a permanent hold of English ground, 

 if it were not from time to time broken up for them by 

 the industry of man, in preparing for the cultivation of 

 other things more valuable to him. On this account 

 those two familiar j)lants are classed with the species 

 introduced originally among agricultural seeds, and still 

 needing some aid from mankind for holding a place in 



