Bibliographical Notices, 137 



of Rosacea; ; Lamiacece gain three, aud Pohjgonacece two places ; 

 while, on the other hand, Cruciferce lose four, Orckidacece two steps 

 in the series. 



What is said of the alpine floras is worth attention as regards the 

 theory of their transport across a glacial sea. We are told (at p,46l) 

 that "the highest flora of intertropical countries at levels bordering 

 on the snow line is not at all identical with the arctic flora by its 

 species, nor yet exclusively so by its genera or even by its orders. 

 The alpine floras of North Africa include few boreal or arctic species. 

 These southern countries have their own mountain floras, bearing 

 considerable resemblance in genera and orders to the arctic floras, 

 but with httle identity among the species. Even on the Alps and 

 Pyrenees there is found a portion only of the subpolar flora ; and 

 along with it are many other non-arctic species, whose affinities are 

 those of the surrounding flora of the plains." And further on, "Itmay 

 be quite true that the change is less rapid and complete among the 

 alpine plants than is the case with those of the plains ; still, as we 

 advance southwards, the polar and arctic species cease to be seen even 

 upon the highest mountains, their place being supplied by other species 

 which have a closer aUiance with the comparatively southern species 

 of the low grounds, and are less adapted to bear extreme cold." 



In Great Britain, the mountain flora " still corresponds with the 

 lower flora of arctic lands, although it wants many of the arctic 

 species. Several of the boreal species fail to reach the hills of Britain, 

 though found in Iceland or Faroe, and numerously in Scandinavia:" 

 and, of our Scottish alpine plants, some very few in turn fall short of 

 the Alps and Pyrenees ; for example, Arenaria rubella, Saxifraga 

 rivularis, Alopecurus alpinus. On the other hand, the British hills 

 possess a few species which do not reach so far north as the polar 

 regions, such as Cherleria sedoides of the Scotch Highlands ; and, at 

 a lower elevation, tlie Irish Saxifrages, Meconopsis cumbrica, and Ile- 

 lianthemum canum are examples of mountain plants which find their 

 polar limits in Great Britain. Still such instances are rare, owing 

 no doubt to the absence of lofty mountains in the south of Britain ; 

 and, for the same reason, the Scottish alpine plants thin-out south- 

 wards, without being replaced by others. 



The higher mountain region is distinguished by the prevalence of 

 Filiees, Juncacece, Saxifragacece, and Caryophyllacece. Allowance 

 being made for the smaller extent of the upper arctic zone, the dimi- 

 nution in species is very striking, since only 262 reach above the 

 height of 700 yards. The lower limits of species of course descend 

 as we advance northwards. Thus, at or near the sea-level in the north 

 of Scotland may be seen Thalictrum alpinum, Carex capillaris, JJryas 

 octopetala, Saxifraga oppositifolia, &c., which, further south, occur 

 only at a certain elevation. 



In the 10th section of this chapter, as often elsewhere, it is urged 

 that the influence of climate is paramount in determining the present 

 distribution of plants — climate being itself the result of physical con- 

 ditions; but exception is taken to the course adopted byiV. DeCandolIe, 

 of measuring its eff"ect by the sum of daily temperatures experienced 



Ann. li^ Mag. N. Hist. Ser. 3. Vol.y'n. 10 



