1 76 ANNALS OF SCOTTISH NATURAL HISTORY 



(3) denizens, or plants capable of surviving and of forming a 

 permanent part of the flora beyond the limits of cultivation, 

 and after it has ceased ; (4) casuals, or plants unable to 

 propagate themselves or to retain their place for more than 

 a brief period. 



These four conditions of permanence are not easily 

 separable, a species frequently belonging to different grades 

 in different districts, or being native in certain districts and 

 clearly an alien in others. It is often almost impossible to 

 determine with certainty whether a species is native or merely 

 a denizen. Where there is a reasonable certainty that the 

 species is alien in Scotland its name is printed in italics ; 

 but where there is room for doubt the name is printed in 

 ordinary type, and the mark }*, or cas., follows each vice- 

 county in which it appears to be alien. 



The presence and distribution of the aliens, and the 

 sources from which they have been brought, throw curious 

 lights on the commerce and social conditions of Scotland in 

 the past and present. 



It seems desirable to repeat here the equivalence of 

 numbers and areas used in the former articles, accepting 

 H. C. Watson's areas : 



WEST LOWLANDS. 72, Dumfries; 73, Kirkcudbright; 74, Wig- 

 town; 75, Ayr; 76, Renfrew; 77, Lanark. 



EAST LOWLANDS. 78, Peebles; 79, Selkirk; So, Roxburgh; Si, 

 Berwick; 82, Haddington ; 83, Midlothian or Edinburgh ; 84, 

 Linlithgow. 



EAST HIGHLANDS. 85, Fife and Kinross ; 86, Stirling ; 87, 

 West Perth and Clackmannan (as far as in Forth basin) ; 88, 

 Mid Perth (from West Perth to rivers Tay and Garry) ; 89, 

 East Perth (east of rivers Tay and Garry); 90, Forfar ; 91, 

 Kincardine; 92, South Aberdeen; and 93, North Aberdeen, 

 separated by watershed passing east and west through Inver- 

 urie ; 94, Banffshire ; 95, Elgin ; 96, East Ness (including 

 Nairn and Inverness-shire, draining to North Sea). 



WEST HIGHLANDS. 97, West Ness (including Inverness-shire drain- 

 ing to Atlantic, and Argyll north of I.innhe); 98, Argyll 

 (between Loch Linnhe and Crinan Canal) ; 99, Dumbarton ; 

 100, Clyde Isles (in Firth of Clyde); 101, Cantire ; 102, 

 South Ebudes (Isla, Jura, and adjacent islands); 103, Mid 

 Ebudes (Mull, Coll, and adjacent islands); 104, North Ebudes 

 (Skye, Rum, and adjacent islands). 



