INTRODUCTOBY EXPLANATIONS. 25 



This list may suffice to convey some idea of the succes- 

 sive re-appearance of species, which a botanist has left be- 

 low him in ascending to the loftier summits of the High- 

 land momitains, and again meets on his retmn downwards. 

 But in descending different hills, he will never find exactly 

 the same order of succession. It may h^ obsen^ed, for ex- 

 ample, that Vaccinium Vitis-Idaea is placed considerably 

 below Calluna vulgaiis and Junipenis communis, in the pre- 

 ceding Kst. Such, however, is not the usual position, or 

 true upper limit of the Vitis-Ida;a. On other hills, it is 

 sometimes found above the CaUima ; even on those hills, 

 upon which the Calluna ascends several hundi-ed feet 

 higher than the altitude (of 2,690 feet) at which it is en- 

 tered in the preceding column of names. And it is very 

 probable that the Vaccinium Vitis-Idsea may grow much 

 higher on some part of Ben-muich-dhu also ; although it 

 was not so obsened in the line of descent, on the day re- 

 fen'ed to. 



The fact of local variations in the comparative heights to 

 which the same species ascend, will be rendered veiy evi- 

 dent by contrasting together two different descents down 

 the same mountain. Ben-na-Bourd, a hill in the same 

 range with Ben-na-muich-dhu, was ascended in 1832, and 

 again in 1844. In the fonner yeai", the species obsen-ed on the 

 broad top, or table land, of the hiU were first noted ; and Eifter- 

 wards all the other species, as successively seen in descend- 

 ing. In 1844, only the half-dozen species, around the 

 cairn on the extreme summit, were first entered together in 

 the note-book ; aftei^wards, all the others seen in descend- 

 ing. In those two years, the descents were made by dif- 

 ferent sides of the mountain ; though with a gi'adual ap- 

 proximation of the two coiu"ses, until both lines of descent 

 came together at about 1,700 feet of elevation. 



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