Aliens and Adventives 97 



New Zealand Alps and uplands, for example, once they have been given 

 the initial assistance required to bring them, should not prove successful, 

 and dominate the English Hills. 1 It is, however, interesting to note that 

 none of the modern introductions of the N. Temperate zone from Japan, 

 N. America, and California, brought for timber or decorative effect, have 

 gone beyond the condition of casual escapes (Aster, Solidago, Lupinus^ 

 Aquilegia, Escholtzia^ etc.), though Oenothera and Mimulus may be referred 

 to as locally naturalized in the south and by the sea. Also one wonders 

 what is wrong when the finest forest-trees of N. America and Canada 

 (Thuya plicata^ Cupressus Nootkatensis^Picea Sitchensis, Pseudotsuga and 

 Sequoia)* do not appear able to compete without assistance with the much- 

 enduring strays of the British Flora. The intense vitality of many of the 

 plants of the British Flora, on introduction to distant colonies, is a matter of 

 general remark ; and older, more isolated Floras (Australia, California, 

 Oceanic Islands) are rapidly devastated by the introduction of the weeds of 

 cultivation. 3 These are not so much the plants of the wild woodland flora 

 indigenous to Great Britain, as * human associates ' similarly introduced into 

 this country from the entire continent of Europe and Western Asia, consti- 

 tuting the most familiar weeds of cultivation, and so maintained in human 

 association over many thousand years. Little reliance can be placed on 

 alleged cases of such plants being found * truly wild ' in any district once 

 inhabited by man. Wherever man goes, he picks up a few more such 

 associates, which follow his cleared ground in enormous profusion : where 

 he can live, they can flourish, and by such unconscious assistance, oppor- 

 tunity may be given for the survival under these new conditions of new 

 races of mutants, some of which may thus appear to gain additional strength, 

 rendering them ' invasive ' where previously they were held in check. 

 British peoples, as essentially corn-associates, unconsciously select any plants 

 which follow the same periodicity as that of the wheat-crop ; and such 

 plants in mass-cultivation, as weeds of a cultivated crop, admit a seed-output 

 which may cover a wastage far in advance of that of local forms just holding 

 their own under conditions of extreme competition. In a formation which 

 has attained a certain degree of equilibrium, and is so far ' closed ', the 

 introduction of seeds of wholly new plants will be a disturbing factor, 

 affecting the wastage of previous occupants. Only by direct experiment 

 does one realize the amount of seed required to produce a few specimens of 

 some admitted ' alien ' in open competition with a cultivated crop ; let alone 

 to establish it in a closed woodland or pasture- formation. 4 



As previously indicated, human occupation of the Oxford district is traced 

 back at least to the Wolvercote sandbank of the Third Terrace, at 250 ft. 

 elevation. The flats of Port Meadow, at 190 ft., indicate some 60 ft. of eroded 

 valley; a process which may have taken 50,000-100,000 years. Palaeolithic 



1 Journal of Botany (1921), p. 354, Colonization of Snowdon. 



8 Sequoia sempervirens (Redwood) is narrowly restricted to the sea-fog zone of the Pacific 

 Slope, and other trees in less degree. 



3 Sinclair (1885), Indigenous Flowers of the Hawaiian Islands, Introduction: 'Forest-fires, 

 animals, and agriculture, have so changed the islands, within the last fifty or sixty years, that one 

 can now travel for miles, in some districts, without finding a single indigenous plant : the ground 

 being wholly taken possession of by weeds, shrubs, and grasses, imported from various countries.' 



Hooker recorded the last plant * farthest South ', as a specimen of Capsella Bttrsa-pastoris , growing 

 at the door of a deserted sealer's hut. For the Dandelion in British Columbia, cf. Journal of 

 Botany, 1922, p. 274: also Thomson, 1922, Naturalization of Plants and Animals in New Zealand. 



4 An arable field adjacent to Bagley Wood, with an aggregate flora of 102 species (including 

 the boundary hedges), gave 73 forms on ground prepared by steam-plough for the wheat-crop. Of 

 these, some 50 were undoubted aliens of the nature of human associates, or assisted types of the 

 indigenous flora whose status is still doubtful. Although only separated from a woodland-clearing 

 by an open gate-space and cart-track, but half a dozen of these last were found inside the wood, as 

 feeble strays for a distance of 20-30 yds. 



