A HISTORY OF NORTHAMPTONSHIRE for distribution. But we also owe many foreigners to the forage which is carried along the line in trucks, from which seeds are spilled, and in this way the small toadflax {Linaria viscidd) has come, no long distance of railways in Britain being without it. The wall rocket {Diplotaxis muralis) is another species which has been introduced in a similar way, and a grass [Setaria viridis), although much less common, is also frequently to be found along the permanent way. Between Roade and Wolverton a very large number of foreign species occur, and the yellow chamomile {Anthemis tinctorid) and the gold of pleasure [Camelina sativd) promise to become permanently established. Just outside our area, in the parish of Hanslope, two foreign species of Hieracium with Anthemis tinctoria cover a considerable extent of the embankment for some distance. Two species of ferns have been introduced to our county quite recently, one the limestone polypody [Phegopteris calcarea or Robertiand) which Mr. Dixon found on the stone banks of the Roade railway cut- ting, and the brittle bladder fern (Cystopteris fragUis). Probably the wind (a little helped possibly by the draught made by rapid trains) has been the agent in these cases, as certainly they were not there formerly, and the spores of the limestone polypody may have been carried by the westerly wind from Cheddar where the plant is frequent. It also exists in Wychwood Forest, Oxfordshire. By the means of railways the Ox- ford ragwort [Senecio squalidus), which previously to their formation was limited in England to Bideford and Oxford, has now been conveyed from the latter place, and especially in recent years, along the Great Western line to Reading and Maidenhead, to Hayes in Middlesex, and to Swin- don in Wiltshire ; and on the London and North- Western Railway to Verney Junction in Bucks ; and it is quite probable before the next twenty years are passed it will have extended along the main line through our county. The striped toadflax {Linaria repens) also, which before the advent of railways was not found north of the chalk area in Oxfordshire and Berkshire, has been carried by trains into our county near Aynhoe, and I have seen it also near Banbury. A great quantity of it was brought to Oxford with railway ballast, and for some years it flourished in great luxuriance, and formed with the yellow toadflax (L. vulgaris) an im- mense number of most interesting hybrids.^ The seeds of the rose bay willow herb {Epilobium angustifolium) may have been partly carried by the wind of passing trains to several places on the sides of the railway. The Canadian water thyme {Elodea canadensis), which was first recorded from Foxton reservoir in Leicestershire, near Market Har- borough, in 1847, and of which a specimen gathered in 1849 from Northamptonshire is contained in the Edinburgh Herbarium, was brought into our area by the Grand Junction Canal, and quickly spread over the county, until in the seventies it was a pest, but since that time it has become less frequent. The same thing has occurred generally over England, waterways having been a principal means by which this rapid spreading of the species has taken place ; but birds ' See the Fiora 0/ Berkshire, pp. 292, 293. 56
