18 



KNOWLEDGE 



[Januaby, 1902. 



become established ; its seeds appear to be killed by a 

 severe winter." It is now natin'aliscd in widely 

 separated stations, chiefly in sandy soil near the sea, 

 and is advancing rapidly in some cases into wild ground. 

 Both of the last^mentioned jilants are widespread 

 European species, and, as miglit be expected, they 

 colonised England prior to thuir invasion of Ireland. 



To an allied category belong those plants, not indi- 

 genous, which ai-e of casual introduction. That they were 

 not inti'oduced with crops is shown by the fact that 

 tlieir headquarters are not in cultivated land, but in 

 situations of different and various kinds, and often of 

 an artificial character. Seeds of these species have come 

 into the country by one means or other in the course of 

 trade and commerce, and when they have happened to 

 fall on suitable ground, they have formed a colony, and 

 sometimes spread widely. The Lesser Toadflax {TAnaria 

 minor), a plant of sandy soils, is spread over almost 



r^^- 



Fio. 1. — Present range of three Irish railway colonists. 



: Linaria minor, first observed about 1819. 



■ '. '. Diplotaxis murulis, „ „ 1833. 



I I Arenaria tenuifolia, „ in 1897, 



the whole of Eiuope, but is not considered native in 

 the British Islands. In Ireland it was introduced early 

 in the nineteenth century. Not finding there the sandy 

 soils which it affects, it invaded the railways, and 

 spreading along the gravelly ballast, has so increased 

 that, excepting the northern counties, it now occurs all 

 over the island. Arenaria tenuifolia has a similar 

 history, except that it is native in England on light 

 soils, and was not observed in Ireland till 1897; it is 

 now known to occur, always on raOway tracks, in 

 fifteen out of the forty Irish county-divisions. Like the 



weeds of cultivation, both of these plants are annuals 

 with numerous small seeds, which are easily transported. 

 The most remarkable of recent Irish immigrants is 

 Matricaria discuidta, a plant like a Chamomile without 

 ray-florets, and possessing a strong agreeable Chamomile 

 odour. It is a native of North America. First observed 

 near Dublin in 1894, it is now spread, often in immense 

 profusion, on railways, roadsides, and waste ground over 

 the whole of central Ireland, embracing neai-ly half the 

 counti-y. This is also an annual, producing a great 

 quantity of minute seeds. 



The most famous of all our colonising exotics is the 

 Water-Thyme, or Canadian Weed {Elor/ra canadensis), 

 whoso dramatic history is well known. Unintentionally 

 introduced from America into Ireland about 1836, and 

 England about 1841, it spread like wildfire through the 

 rivers and canals, threatening to choke the water-ways, 

 and caiTying consternation to the hearts of the local 

 authorities responsible for water-traffic and drainage. It 

 has now paused in its wild career, and remains a 

 perennial member of the flora over a gi-eat portion of 

 the British Isles. Another American plant, and one 

 whose status is far more difficult to determine, is the 

 Rush, Jiinrus tenuis. During the last forty years this 

 plant has been found in many European counti-ies, and 

 in these islands in Scotland, Wales, S.W. England, and 

 West Ii'eland, chiefly on roadsides in uncultivated 

 districts near the sea. If it is native, it is hard to 

 credit its being so long undetected ; if introduced, the 

 difficulties of accounting for its wide distribution in 

 wild regions, far from centres of dispersal, are equally 

 staggering. It is, naturally, near the centre of tratle 

 that foreign immigi-ants most abound. About docks 

 and railway sidings, flour mills and distilleries, and 

 ballast heaps, we may gather, sometimes by the score, 

 waifs from many parts of the world. Many of these 

 are old acquaintances, loafers in half the seaports of 

 the land; for instance, Lepidium Draha, Erysimum 

 orientate, Silene Armeria ; and various species of 

 Sisymbrium, Malva, Me/i/otus, Xanthium, Echinosjn r- 

 mum, Bromus, and so on, drawn from various pai-ts of 

 Europe and America, swell the motley crowd. 



The cultivation of pot-herbs and simples, though now 

 almost fallen into disuse, has bequeathed to us a varied 

 and extensive legacy of plants of doubtful standing. 

 The domestic use of many such species in these countries 

 dates back to the Roman occupation, and in eai'ly 

 Christian times the spread of monastic establishments 

 distributed medicinal and culinary herbs all over the 

 country, for the monks were skilled in leechcraft and 

 gardening. As in other cases, it is now often difficult 

 to determine in what instances the plants were derived 

 from aboriginal stock, and in what cases they were 

 impoi-ted and have since run wild. The great Leek, 

 Allium Bahingtonii, is widely distributed among native 

 plants along the west coast of Ireland, and grows also 

 in Dorset and Cornwall ; yet there appears a strong 

 probability that it is a relic of ancient cultivation. 

 Several other Leeks, and many Mints, have the same 

 story. The Good King Henry (Chenopodium Bonus- 

 Henricus), Cai'away (Carum Carui), and Parsley 

 (PetroseHnum sativum) aie more evidently of cultivated 

 crigin, still haunting chiefly the vicinity or sites of 

 dwellings. The noble Elecampane (Inula Uchnium) was 

 formerly in great repute as a pectoral and stomachic 

 medicine, as witnessed by the old Latin adage — 



Enula Canipana reddit praeordia saiia. 

 Its candied rootstock is still used as a sweetmeat. A 

 few years ago I came across a colony of this plant which 



