Arctic Plants: Concluding Remarks 133 b 



The following list will show an assemblage of species which accompanies 

 the Pyrola alliance on this continent (Maryland and Virginia) and in Europe 

 (Denmark). 



Maryland and Virginia Denmark. 



Chimaphila umbellata C. umbellata. 



.C. maculata Moneses unifiora. 



Pyrola secunda P. secunda. 



P- chlorantha p. chlorantha. 



P. rotundifolia ' p. minor. 



P. elliptica p. media. 



Monotropa lanuginosa M. hirsuta. 



M. unifiora 



Goodyera pubescens G. repens. 



Corallorhisa odontorhiza C. innata. 



Cypripedium acaule 



Orchis spectabilis 0. mascula. 



Hieradum venosum H. murorum. 



Vicia caroliniana V. sylvatica. 



and a little farther north : 



Linnaea borealis var. americana L. borealis. 



Trientalis americana T. europaea. 



To this list, which only shows some parallel species or genera, may be 

 added several other plants which are also associated with the Pyrolaceae in the 

 vicinity of Washington (D.C.), for instance: Epigaea, GauUheria, Mitchella, 

 Obolaria, Cunila, Gerardia, Leptandra, etc. 



From this enumeration may be seen that while the Pyrolaceae have kept 

 unchanged, their associates Linnaea and Trientalis represent geographical races, 

 the others being species totally distinct. 



It is thus an indisputable fact that the Pyrolaceae do occur in their typical 

 form in both Worlds, besides that they, at least some of them, may acquire a 

 more or less modified structure in the various districts where they occur, in the 

 manner of "geographical races." 



In view of these facts it seems difficult to explain the present distribu- 

 tion of the Pyrolaceae in any other way than that they have been produced 

 "not in one area alone," but in several. For if the family had originated on this 

 continent and later on migrated to Europe, we might be entitled to expect that 

 some of their associates would have accompanied them; of such we have only 

 Linnaea and Trientalis both of which represent geographical races, however. 

 But referring to the other plants, none of these has ever been found in Europe. 

 Would it not be natural to expect that at least the allied genera Epigaea and 

 GauUheria, showing the same habit as the Pyrolaceae and extending far north 

 on this continent, might have accompanied the Pyrolaceae on their migration 

 to Europe? Westward, on the other hand, we find in Japan Epigaea asiatica 

 Maxim., Mitchella undulata Sieb. et Zucc, and Monotropa unifiora. 



It is really astonishing to observe how such an alUance of a few closely 

 related plants have been able to preserve their habit and structure at such 

 enormous distances, as shown according to the longitudes and latitudes, within 

 which they exist. 



If the species had been alpine and arctic at the same time, their distribution 

 would be explained in quite a different way, as being the result of migration 

 during the glacial epoch. But now that they are mainly lowland types, their 

 habitat being mostly the wooded belts, the problem of their range calls for 

 another explanation, viz. : the probability of their development from more than 

 a single area. 



24657—10 



