494 X. GENERAL REMARKS. 



heath on some few hills, whei-e the limits of the heath 

 itself did not appear unduly depressed, the latter has been 

 deemed to have naturally a somewhat lower limit than 

 the tormentil. 



Similar considerations have induced the assignment of 

 Nardus stricta to the superarctic zone ; although the 

 name of this grass is placed underneath that of Calluna 

 vulgaris in the list of upper limits on page 325, where 

 they stand thus : — 



Calluna vulgaris, 1100 1080 1060 yards. 

 Nardus stricta, 1100 1070 1060 yards. 

 These altitudes were noted on the Ben-na-bourd range of 

 hills in Aberdeenshire. On various other hills, in the 

 same and other counties, where both Nardus and Calluna 

 fail to attain 1060 yards, the grass was observed higher 

 than the heath ; and it was accordingly assigned to the 

 zone above that which was made to correspond with the 

 upper limit of the Calluna. 



In both the examples thus cited by way of explanation, 

 and in other similar instances, a further circumstance has 

 been taken into account towards a decision in doubtful 

 cases. The Calluna is very conspicuous on the mountain 

 acclivities ; and having been adopted as a test or charac- 

 ter of the midarctic zone, its highest places were carefully 

 looked for, and probably very seldom overlooked in any line 

 of descent. On the contrary, a grass or other small herb, 

 is much more likely to be overlooked, especially if in leaf 

 only. And moreover the Nardus, Anthoxanthum, and 

 Tormentilla were not particularly looked for, though 

 doubtless noted as soon as observed, while descending 

 from the summits of high hills. On such account there 

 seems to have been much greater chance for the names of 

 any of these three herbaceous plants being occasionally 

 entered too low in manuscript lists, than there was for 



