xiv INTRODUCTION 



latter are Calotis cuneifolia achenes, and characterise 

 especially wool imported from Sydney (N.S.W.). 



Alien weeds have sometimes been traced to imported 

 skins, hides, and furs ; and considering that a million 

 hundredweight of cow-hides and loo million skins of 

 other kinds are imported annually, this source of intro- 

 duction might be expected to be an important one. Horti- 

 culture is responsible for a large number of aliens which, 

 having been imported for ornament or for medicinal 

 purposes from early times, have now become naturalised. 



Hay importation is an obvious source of meadow weed 

 introduction ; the aliens traced to it are, however, not 

 numerous, because it is only exceptionally that large 

 quantities of foreign hay are imported. 



Seaside plants have frequently been introduced in 

 ships' ballast, especially to ports such as Swansea, which 

 export much more merchandise than they import. 



Trees and shrubs have frequently been planted among 

 the indigenous vegetation to improve the quality of 

 woods, to afford cover for game, and for other reasons. 

 Such species, whether established and spreading them- 

 selves or not, often get recorded in local Floras. 



The flora of railway banks has received much attention. 

 It is composed of numbers of different elements intro- 

 duced at different stages in the history of the lines. The 

 development of vegetation on the newly made banks of 

 the M. S. & L. Railway Extension near Rugby was noted 

 by the writer in 1897-8, and was the subject of a paper 

 published in the Rugby School Natural History Society 

 Report for 1898. 



Summary. Out of the 924 aliens enumerated in the 

 Flora, 123 are old-established weeds of uncertain origin, 

 332 are due to horticulture and arboriculture, while 206 

 are grain-sifting aliens of recent appearance and of little 

 permanence. Of the 170 species referred to in square 

 brackets, the greater number are common weeds which 

 have usually been recorded in our local Floras from 

 artificial habitats only, but which the author for various 

 reasons believes to be true natives. 



