312 Vn. AREAS OF SPECIES. 



Avbutiis aljiiiia 15 16 17 18 Forfar to Slielland. 



Pyrula uniflora 15 - 17 18 Peitli to Hebrides. 



Juncus balticus 15 - 17 18 Forfar to Hebrides. 



Eriocaulon septangiilare 16 Norlb and Mid Ebudes. 

 Pinguicula alpina 16 17 North Ebudes. East Ross. 



Ajuga pyramidalis 16 17 18 Westerness to Orkney. 



Hierochloe borealis 17 Caithness. Forfar? 



Primula scotica 17 18 Suthd. Caithness. Orkney. 



Ceraslium nigrescens 18 Shetland only. 

 Arenaria uorvegiea 18 do. do. 



IV. EXPLANATIONS OF THE AKEAS OF SPECIES. 



The three lisis placed under the title 'Areas of Species' present an 

 arrangement of the plants which bears a direct relation to the geo- 

 graphical spaces over which they are distributed in this country ; with a 

 less direct relation also to iheir climates, as shown by general tempera- 

 ture, &c. The plants of the antecedent lists are here re-arranged-|)ri- 

 mari'y into three leading groups or divisions, thus ; — 



A. Austral species, successively ceasing in the northerly direction. 



B. General species, all far extended, though not equally far ex- 



tended, from south to north. 

 C Boreal and montane species, successively ceasing in the 

 downward and southeily direction, — or, the same thing, suc- 

 cessively appearing to the observer who advances northward 

 and upward. 

 These three divisional groups are broadly distinct only at their non-con- 

 tiguous extremes. As here placed, they may be deemed to pass gradu- 

 ally into each other. In each of the three divisions certain species are 

 to be found, which might have been placed in a different division with 

 almost equal propriety. Thus, Viciasylvalua (page 305) is represented 

 as found in every province from 1 to 17 inclusively, and might have 

 been placed among the general species so circumstanced (page 302) ; 

 although its decreased frequency in the more southerly provinces led to 

 its inclusion among the boreal plants. In like manner, Hut>hinsia 

 petrcta (page 305) corresponds with various austral species by its early 

 northern termination ; but it is placed in the third division on account 



