GENERAL HABITAT. 



23 



secondary Flora} But the number of these species is so small, and the area, affected by 

 them are so evidently only the temperate complements of adjacent Arctic or Alpine areas 

 that it does not become necessary to recognise for the genus any temperate province!.! 

 For this reason, and with the exception of the northern Circumsolar province itself, the 

 various provinces are indicated by the mountain systems and differentiated by the inter- 

 vening seas and plains of the northern hemisphere. 



The evidence from the distribution of any single large genus being the converse of 

 that from the composition of local floras, an attempt is now to be made to estimate the 

 value of such evidence by delimiting the various Arctic-Alpine provinces from tli ir 

 species of Pedicularis alone. 3 Its application requires the recognition of eight provinces, 

 the names and limits of which are given below. Each province is expressed in terms of 

 its " endemic percentage," sueh districts as increase this factor bein" ail led together 



n ^ v , v 



pro 



such as diminish it being removed. Thus in the delimitation of the Circumj 

 it is found to be necessary to add to it the peninsulas of Kamstchatka and Alaska, which 

 appear to be natural districts and seem conjointly to form a natural division. Tl 

 alternatives open are to unite both to America, to Japan, or to Siberia; to unite 

 Alaska to America and to apportion Kamstchatka either to Japan or to Siberia 

 finally, to look upon the two as forming a province apart. The last is an inadmissihl 

 course, since their removal from the Circumpolar province decreases its endemic percentage 



If both, or if Alaska only, be united to America, the endemic percentage both f the 

 Circumpolar province and of America is diminished by the act, and a similar result also 



happens if both, or if Kamstchatka only, be united either to Japan or to Siberia, Jt 

 is probably not altogether an accident that the Northern Summer Isothermal of 15°C 

 the best graphic index of the temperature conditions that chiefly affect circi 



mp 



>-> 



vegetation (mean annual temperature being obviously of very subordinate importance) 

 should coincide so exactly with the distribution of circumpolar Pcdiculares. But although 

 this coincidence occurs, and although this Isothermal is therefore employed as the most 

 convenient expression of the boundary of the Circumpolar province, it is to be distinctly 

 remembered that the existence of this line is not a factor in the process of reason i; 

 whereby the actual delimitation is effected. Similarly neither physiographical featui 

 nor climatic conditions have been used in the delimitation of the other seven provinces, 

 since it is plain that without a rigid adherence to evidence derived from morphology 

 alone in the definition of biological areas, the ultimate comparison of biological with 

 physiographical and meteorological facts becomes a process of circular reasoning. 



The Circumpolar province is bounded by the Northern Summer Isothermal of lo°C. 



•8 successively on the European, Siberian, Japanese, and American provinces. It 



contains 20 species, & of the whole; of these 10 are endemic, and one other is 



and borde 



presented only by an endemic variety .—the endemic percentage is thus 52 



Thiselton-Dyer: 



field fi 



14, where and 



in the subsequent pages a most excellent working system of Plijtogeography is outlined. 



* It seems advisable to avoid the use of the term Region, as this word has unfortunately become stereotyped in 

 England and in Germany to indicate areas of different value, and because there is no special aptness in either the 



English or the German employment of the word. 



^ 3 Mr. Maximowicz says the time has not yet arrived for a final discussion of the distribution of this genus {Mel. 

 Biol, xfi, 783). This is quite true; still our knowledge of six of the provinces is certainly fairly complete, and of 

 the remaining two (Tibflto-Chin* and Himalaya) probably fairly representative (see footnote 1, p. 58;. 



• 



