Natives and Aliens. 



Somf! trouble has l)epn taken in the present compilation with regard to the 

 difficult question of native and non-native species. Much confusion and want of 

 uniformity of treatment exist in local Floras on this question, owing partly to its 

 inherent (lifficulties, hut in great measure to the lack of clear thinking. In 

 studying vegetation from this standpoint, several courses are open to the botanist. 



We may argtie, as Woodruffc Peacock did,' that since man is a j)roduct of 

 nature, his operations should rank as natural processes, not to be distinguished 

 as regards plant dispersal from those carried out by the beasts and l)ird8. Pur- 

 sued to its logical limit, this view would lead us to include in the local flora every 

 plant gTo\\ ing within the area, from true natives to specimen conifers, potatoes, 

 and tropical orchids. 



A more usual and less e.xtrenie view would take no cognisance of species planted 

 and maintained by man. such as crop plants and the contents of gardens and 

 greenhouses, but would include in the flora all casual followers in man's train- 

 plants introduced in the course of agriculture and commerce, and maintaining 

 themselves by man's assistance, in the way of keeping down the native vegetation 

 by cultivation, &c. This is approximately the view of the Moia of Sorth-Eatt 

 h-eland, in which such dependents as the Poppies and Fumitories are included 

 in the flora without coninient. In many other works {^e.y. " Cybele Hibernica," 

 " Irish Topographical Botany") an attempt is made to go further, by using signs 

 meaning "possibly introduced," "proi)ably introduced," ' ' certainly introduced," 

 &c. But these terms are vague and need clear definition. 



When we think how catastrophic has been the influence of man during the last 

 couple of thousand years upon the pi'eexisting vegetation, biult up by the slow 

 processes of competition, migration, and secular change, and how unstable and 

 e])hemeral is the vegetation which occupies the area of his occ\ipation, it seems 

 desirable from every point of view, and especially from that of the study of plant 

 geograjihy, to separate, in an analysis and discussion of the flora, so far as we can, 

 the pre-human flora from that which has resulted from the practice of agriculture. 

 In countries such as our ow!i, where almost every portion bears the imprint of 

 man's handiwork, this is not always easy, and can only be attempted with a clear 

 understanding of the problem, ^^'e aim at leconstructing the aboriginal flora 

 from a study of that tlora on the area at the present time. What are the tests 

 to be employed? What do we mean by an aboriginal or truly native plant t' It 

 has seemed to the writer that the definition of S. T. Dunn,* provides the most 

 convenient answer to the question :— a native plant is one which has spread by 

 natural ( \.e. non-human) means from a natural source to a natural habitat. Three 

 points are thus involved -jiarentage, dispersal, habitat -and human influence on 

 any one of the three will rule a plant out from ranking as fully indigenous. An 

 example of failure on each of these three points will make the test clearer. 



1 !•;. A. WoodrntTe-Peacock : Nattrenantl Alienn. ".louni. of l!ol.', xlvi. :Mi». 1908. 

 - .S. T. Duini : Tke Alien Flora i\J' Uiituin, \>.\. 



