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FURTHER ADDITIONS TO THE FLORA OF WESTERN 



OREGON 



By J. C. Nelson 



In this journal for February, 1918, I printed a list of plants 

 growing spontaneously within the limits of Piper & Beattie's 

 Flora of the Northwest Coast that had not found mention in 

 that manual. I ventured the assertion at the time that further 

 field-work would materially add to this list, not only because 

 of the rapid introduction of foreign species, but also because the 

 geographical limits of many native forms are not clearly under- 

 stood. The list which appears below, representing the result 

 of another season's collecting, seems to show that my prediction 

 was not wholly unjustified. In spite of the fact that I made 

 only one trip this year that took me more than ten miles from 

 home, the number pf unreported species shows no falling off 

 from previous years. 



In the case of the foreign plants, there is nothing specially 

 remarkable about this — in fact, it is what is taking place in much 

 the same degree on the Atlantic seaboard. The weed-flora of all 

 sections of the temperate zone tends toward a certain uniformity; 

 and this tendency becomes more marked as means of transpofr 

 tation multiply. The process may be compared to the diffusion 

 of a liquid through another medium — and the point of saturation 

 is still far away. Individual species may appear and disappear, 

 but the rising tide of the aggregate shows a steady increase. 



The native species that have not .appeared in previous lists 

 seem to fall into two general classes: (i) Californian species 

 that were thought not to extend north of the Umpqua Valley; 

 (2) plants characteristic of the Upper Sonoran Zone east of the 

 Cascades, which on account of the humidity of western Oregon 

 were not expected to occur here. In regard to the first group, 

 there is of course no a priori reason why the Californian flora 

 may not extend beyond the limits assigned to it. The state 

 line simply does not exist on a botanical map; and there is neither 



