DISTRIBUTION OF WEEDS 17 



from grassy areas, while forget-me-not, field speedwell, fool's 

 parsley, and persicaria are among the arable weeds that have 

 been observed to be distributed in this way. Many weed 

 seeds are rather sticky when damp and tend to adhere closely 

 to anything they touch, so that they are easily carried about 

 from one place to another. 



(e) Distribution by High Winds and Storm Columns. Very 

 little seems to be known on this subject, but one observer, 

 WoodrufTe Peacock, has specially studied the point, 1 and his 

 results suggest that this is a far more important means of dis- 

 tribution than is generally recognised. Ordinary wind drift 

 will carry seeds some distance, but this is very local. Wood- 

 rufTe Peacock cites a case of such distribution of charlock 

 recorded in Thompson's " History of Boston," and if this could 

 be more universally established it might throw some light 

 on the continual appearance of charlock when grass land is 

 ploughed up, or old arable land free from the weed is ploughed 

 more deeply. Seeds of mithridate mustard (Thlaspi arvense) 

 in Cadney (Lines) were carried by a single spring gale over 

 half a mile of arable peat. Whirlwinds or small local storm 

 columns will lift and shift seeds for distances up to 1 50 yards, 

 but storm columns can carry materials for miles. Distribution 

 over an area of at least twenty-five miles has been observed in 

 Lincolnshire. In 1897 a storm column brought to Cadney 

 a variety of plants for which the nearest habitat was twenty 

 to twenty-five miles away. Among these were wild onion 

 (Allium vineale) and couch grass, while heavy plants of tufted 

 vetch (Vicia cracca), including the root, were also carried. A 

 list of the plants that WoodrufTe Peacock has personally noted 

 to be carried by storm columns in this country may*be inter- 

 esting, as so little information on the point is available : 



Many grasses. 



Achillea millefolium (yarrow). Cut fragments. 



Allium vineale (wild onion). Rooted plants. 



Anthriscus sylvestris (wild chervil). Fragments. 



Capselta bursa-pastoris (shepherd's purse). Rooted plants. 



Cerastium vulgatum (mouse-ear chickweed). Rooted plants. 



Hippocrepis comosa (horse-shoe vetch). Rooted plants. 



Leontodon autumnalis (autumnal hawkbit). Cut fragments. 



Lotus corniculatus (bird's foot trefoil). Rooted plants. 



1 WoodrufTe Peacock, E. A. (1917), " The Means of Plant Dispersal," 

 Selborne Magazine, XXVIII, pp. 40-44. 



2 



