Southeastern Washington and Adjacent Idaho. 109 



Crataegus brevispina and Amelanchier florida form dense 

 thickets, sometimes singly, but more often in mictium. Fre- 

 quently these copses are so dense as to exclude all other vegeta- 

 tion. In the month of May when these trees are clothed with 

 their profuse white blossoms the flood-plains are indeed a beauti- 

 ful sight. Even in winter the woodland growth along the 

 streams, as they wind their way among the treeless hills, lends 

 pleasing variety to the monotonous landscape. 



RUDERAL VEGETATION 



There are a number of plants that are regularly found in and 

 about waste places. To this number may be added others that 

 are regular members of certain of the preceding plant communi- 

 ties which now and then reveal a decidedly ruderal tendency. 

 The following list includes the commoner plants of this nature : 



RUDERAL SPECIES 



Amaranthus blitoides Dipsacus sylvestris 



Amaranthus graecizans Erigeron canadensis 



Amaranthus retroflexus Er odium cicutarium 



Amsinckia intermedia Geranium pusillum 



Anthemis cotula Madia glomerata 



Arctium lappa Marrubium vulgare 



Artemisia atomifera Matricaria matricarioides 



Artemisia gnaphalodes Polygonum aviculare 



Bromus brizaeformis Salsola kali tenuifolia 



Chenopodium botrys Sanguisorba annua 



Chenopodium album Sisymbrium altissimum 



Cirsium lanceolatum Vaccaria vaccaria 



Collinsia tenella Verbascum thapsus 



Because of the practice of alternating a crop of wheat with 

 summer fallow nearly half of the farmed area is laid bare each 

 year for the invasion of ruderals. Amaranthus graecizans and 

 A. retroflexus are the dominant weeds of these fallow fields. 

 Unless the ground is frequently tilled these grow in great abun- 

 dance, the former breaking loose near the surface of the soil in 



109 



