A FLORA IN NORTHERN OREGON 319 



areas we have described is the exposure to winds. Nearly all 

 the taller plants in the less protected situations are bent very 

 perceptibly to the eastward, the prevailing winds being from 

 the west; this is notably true of trees and shrubs that have 

 been planted in the town. 



We will now consider briefly the various associations of 

 plants that are found in these several situations. These forms 

 that occur very sparingly in any locality, or are much more 

 characteristic of one of the other associations are omitted from 

 tlic list for that locality. 



The species occurring along the immediate margin of the Co- 

 lumbia, or at least within the direct influence of the copious 

 water supply are as follows : 



Marsilia vestita Veronica peregrina 



Juncus bufonius Verbena hastata 



Salix amygdaloides Iva axillaris 



Salix exigua Euthamia occidentalis 



Polygonum emersum Coreopsis atkinsoniana 



Roripa columbiae Gaillardia aristata 



Roripa curvisiliqua Helenium autumnale grandiflorum 



Roripa obtusa Artemisia dracunculoides 



The Marsilia is extremely abundant. The willows form low 

 thickets in places, which are nowhere very extensive. Roripa 

 columbiae is a peculiar species, of very limited distribution, ap- 

 parently mainly confined to the banks of the Columbia in east- 

 ern "Washington and Oregon; it is not common here. The 

 Coreopsis, Gaillardia, Helenium, and Artemisia are especially 

 plentiful. Several introduced plants, especially the Russian 

 thistle and Atriplex hastata are common here, but are more char- 

 acteristic of the next higher association. This list is a very 

 short one, in spite of the abundance of moisture. This is due 

 largely to the fact that the land here is nearly all below high 

 water mark, and the late floods prevent many species from se- 

 curing a foothold. 



Between the moist margin of the river and the more elevated 



country, lies the low sandy tract above mentioned. The soil 



here is dry but not excessively so, and supports a fairly distinct 



iciation of plants, though several of the species are equally 



characteristic of the higher section. Here we find : 



