180 



4- Species not occurring south of Washington, but with an 

 eastern range, to Idaho, Montana, Colorado, etc., ']2. 



5. Species occurring in Washington and Oregon only, 114. 



6. Species not occurring south of Oregon, but with an east- 

 ward range, 67. 



7. Species extending from Washington to California, Nevada 

 or Arizona, 364. 



Of the above list, 115 are species that are definitely referred 

 by the author to the Upper Sonoran Zone. 



The number of these Washington species which are either re- 

 ferred outright to British Columbia in Piper's statement of 

 range, or given a range that would justify us in expecting them 

 in the Province, is 107, of which 19 are introduced. In both 

 manuals therefore, the extreme margin of probable error is not 

 excessive. 



A careful study of all these differences and discrepancies leads 

 to two conclusions: 



1. That Washington, partly because of the different climatic 

 conditions due to its more southern position, and partly because 

 of its topography, is a region of more marked endemism than 

 British Columbia. 



2. That although artificial boundaries are usually wholly 

 without significance in determining plant-distribution, the 49th 

 parallel seems to come very near to a line that marks the extreme 

 northward dominance of the Californian flora on the one hand, 

 and the extreme southern extension of the Alaskan or sub-arctic 

 flora on the other. As far as the introduced plants are concerned, 

 their occurrence or non-occurrence is a matter of very slight" 

 significance, since their establishment at any particular station 

 is usually the result of pure accident, and no obstacle to their 

 further spread will usually exist. Some further details of the 

 differences between the two Floras may be of interest. 



Fifty-five genera represented in Henry are not found in Piper, 

 but 30 of these include only introduced species (among these 

 Ulmus with 3 species, Dianthus, Cynosurus and Vinca with 2 

 each, and 26 others with one each). Androsace with 4 species is 

 the largest indigenous genus not represented in Piper, next come 

 Limnanthes and Primula with 2 each, and 22 others with one each. 



