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INTRODUCTION TO PLANT GEOGRAPHY 



situated in one altitudinal zone and another in another zone not 

 directly adjoining ; and (5) when diffuse, bipartite, or otherwise, 

 and populated by identical forms, it is said to be homogeneous — as 

 opposed to the heterogeneous discontinuity that involves related or 

 vicarious forms occupying different component parts of the range. 



As for more specific types of discontinuous ranges, we may 

 mention the following as being among the most familiar and 

 important : 



(i) Arctic-Alpine — distributed in the arctic region and in moun- 

 tain systems of temperate or even warmer zones ; examples are the 

 Herb-like Willow {Salix herbacea) and the Purple Saxifrage {Saxifraga 

 oppositifolia agg.), see Fig. 49. 



Fig. 54. — Map showing range of species oi Plat anus (Plane-trees, or Buttonwoods). 

 (After Fernald, emended.) 



(2) North Atlantic — distributed in North America and Europe, 

 and sometimes also locally in Asia ; examples are the familiar 

 Bog Club-moss {Lycopodiiim imindatiim) and the Hooded or Droop- 

 ing Ladies'-tresses (Spiranthes romansoffiana), see Fig. 50. 



(3) North Pacific — distributed chiefly in North America and 

 Eastern Asia, though sometimes elsewhere ; examples are afforded 

 by different species of Torrey Pine {Torreya) and by the Skunk- 

 cabbage [Syniplocarpus foetidiis), which is one of that remarkable 

 group of species common to eastern Asia and eastern North America 

 but wanting in the regions lying between — see Fig. 51. 



(4) North-South American — distributed in North and South 

 America but lacking continuity between ; an example is afforded 

 by the members of the Pitcher-plant family (Sarraceniaceae), see 

 Fig. 52. 



(5) Europe-Asian — distributed in Europe and Asia but lacking 

 continuity between ; examples are Leontice altaica and Cimicifuga 

 foetida, see Fig. 53. 



