132 NOTES ON THE DISTRIBUTION OF 
their appearance accidentally at high altitudes, as are alpine 
plants to intrude upon the lower haunts of the former. It 
will be observed, that these remarks are only strictly true, 
of a district, which includes a range extending from the sea- 
level to several thousand feet above it. Rivers are the chief 
agents by which plants of the higher are conveyed to the 
lower districts. 
If now and then, a solitary tuft of Epilobium alpinum, 
Saxifraga aizoides, Oxyria reniformis, Festuca vivipara, and 
Alchemilla alpina appears not far from the sea and near its 
level; this, (on the supposition that they have not been wil- 
fully introduced by man), can only happen in the vicinity of 
some stream, which traverses, or some of whose tributaries 
pass through, a mountainous district. Such is the case with the 
plants alluded to, in the vicinity of Aberdeen ; and they prê- 
sent us with examples of what I have ventured to call acci- 
dental stations. a 
It is quite likely that, after a time, some species, thus EE 
conveyed far from their natural places of growtb, may in- 
. crease rapidly, and become established in such localities; SO — 
that it would be ultimately impossible to ascertain whether 
they had, or had not, been introduced in the way alluded 
to. 
Mr. H. C. Watson, in his second paper, (Lond. Journ. Bot. 
May, 1842) makes the remark, that “ All alpine species 
have not an equal tendency to descend into dark valleys, 0T - 
along the courses of streams ; or to grow upon shaded rocks, : 
E 9r near the sea-shore. The consequence is, that in such $t - 
_ tuations several species are occasionally found, far below - 
others, with which they are naturally associated by climate, 
when they grow in similar situations ; and their absolute al- 
titude thus becomes an imperfect guide to their true relative 
positions as determined by climate.” A question arises, 
therefore, by what means we are to ascertain the lowest na- 
tural limits of such stragglers ; and it is one which cannot be 
answered with certainty, except as by attending to the asso- 
ciations of such plants and their comparative abundance, We- 
