36 INTRODUCTORY EXPLANATIONS. 



geogi'aphy to bear this in recollection ; othenvise, the zonal 

 or climatic distribution of plants will appear- a chaos of 

 confusion and contradictions, instead of being one of the 

 most interesting aud instmctive inquiries with which a bo- 

 tanist of philosophical tiu'n of mind can engage himself. 



The Arctic Region is conveniently sub-divided into its 

 tlu-ee zones by the tenninal lines of Erica Tetralix and 

 Calluna vulgaris ; the middle zone being that space which 

 is situate above the hmit of the Erica, and is still within or 

 below that of the Calluna. To keep up some uniformity 

 of tenns, as more easily remembered, the tluee zones of 

 the arctic region may be appropriately designated the 

 Super-arctic, Mid-arctic, and Infer-arctic zones. The 

 test derived from the presence or absence of the two shiiibs 

 mentioned, is more obvious and easily apphed in the High- 

 land pro\ances, than is the case in those more southward, 

 where the Ericaceous shmbs are more frequently or more 

 completely destroyed by the fire-brand of the farmer and 

 shepherd. But with the descriptions and explanations to 

 be given in an after pait of this work, the tluee ai'ctic zones 

 will be rendered sufficiently clear and certain. 



It is in the mid-arctic zone, as will be then more fully 

 shown, that collecting botanists find most of the rare alpine 

 plants which they so much dehght in procming ; and to 

 collect which, is the sole object of nineteen out of twenty 

 botanists who ascend the mountains. In this zone, for ex- 

 ample, grow Saxifraga nivalis, Gentiana nivalis, Erigeron 

 alpinus, Astragalus alpinus, Veronica alpina, Alopecm'us 

 alpinus, &c. &c. Several of these plants rise also into the 

 super-arctic zone ; to which some few others are perhaps 

 wholly limited, as Saxifraga cemua and Saxifi-aga ri\ailaris. 

 Many of the more ordinary alpine plants occur in all the 

 three arctic zones, and descend also some distance >vithm 

 the agrarian region ; for example, Thalictrum aljiinum, 



