Botany and Zoology. 147 



States under the same annual isotherms, indicates the advantage of a mean 



summer heat. For lack of that, doubtless, very many of the introduced deni- 

 zens of Britain would soon disappear, if deprived of human care. 



"The northern limit to which vegetation extends varies in every longitude; 

 the extreme is still unknown ; it may, indeed, reach to the pole itself. Phoe- 

 nogamic plants, however, are probably nowhere found far north of lat 81°. 

 Seventy flowering plants are found in Spitzbergen ; and Sabine and Ross col- 

 lected 9 on Walden Island, towards its northern extreme, but none on Ross's 

 Islet, 15 miles further to the north." 



Saxifraga oppositifolia is probably the most ubiquitous, and may be consi- 

 dered the commonest and most arctic flowering plant" There are only eight 

 or nine phmnogamous species peculiar to the arctic zone, and only one pecu- 

 liar genus, viz. : the grass, Pleuropogon* Of the 762 found south of the circle, 

 iced beyond lat. 40" N., in some part of the world ; 



about 50 of them are identified as n 

 tropics and 105 as inhabiting the south temperate zone. , ^, , , 



the proportion of species which have migrated southward m the Old and 

 Jew World also bear a fair relation to the facilities for migration presented by 

 me different continents." The tables given to illustrate this " present m a 

 very striking point of view the fact of the Scandinavian flora being the most 

 ^idely distributed over the world. The Mediterranean, South African, Ma- 

 layan, Australian, and all the floras of the New World, have narrow ranges 

 compared with the Scandinavian, and none of them form a prominent feature in 

 any other continent than their own. But the Scandinavian not only girdles the 

 globe m the arctic circle, and dominates over all others in the north temperate 

 ^one of the Old World, but intrudes conspicuously into every other temperate 

 flora, whether in the northern or southern hemisphere, or on the Alps of tropi- 

 cal countries." * # * « Tn nno rfisnert. this micrration is most direct in the 







judes ThislTave'ac^counted forlriorrAntarctTca, p. 230)ty Ae continu- 

 ous Cham of the Andes having favored their southern dispersion. 



In presenting the actual number of arctic species, and in delineating their 

 geographical ranges, the question, what are to be regarded as species, be- 

 comes all important As to this, it does not so 'much matter what scale is 

 Jdopted, as to know clearly what the adopted scale is. Here we are not left 

 m doubt Taking European botanists by number, we are confident that nine 

 «»t of ten would have enlarged the list of 762 phsnogamous arctic species to 

 2 or more, and would not have recognized a goodly number of the synonyms 

 Jf-iuced, thereby considerably affecting the assigned ranges especially into 

 ^^mperate and austral latitudes In this regard we should side with Ur. 

 '^^'■''^'T on the whole, but with differences and with questionings-witii halt- 

 '-^>tf>P« following his bold and free movement, but P^^^^'^ ^^j^J^^^Hoo^r 



...u in re££ to Z ll^^^^^^ch ^^ --oir is based. 



^ ■■ " if, with many botanists, we consider tliese closely allied varieties 

 ■;■ • 'pvcios as derived bv variation and natural selection from one parent form 

 "^ =^ comparatively modern epoch, we may with advantage, for certam purposes, 

 ,. * ^onffln^a U mentioned in another place (p. 269) as an absolutely peculiar arc- 

 J or arotic-nlpine jjenu'^ of E. America. But we have considered this genus as 



J,?[-de-s JouVnil^oJaurrvsfs'r^his 'original article But tins article 

 l^^ found in the velum; of th^t Journal for 1827; so that the name I><y,cglas^a 

 '^ adopted, if the genus is sufficiently distinct from Androsaee. 



