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 
Amaranthus graecizans 
Amaranthus retroflexus 
Amsinckia intermedia 
Anthemis cotula 
Arctium lappa 
Artemisia atomifera 
Dipsacus sylvestris 
Erigeron canadensis 
Erodium cicutarium 
Geranium pusillum 
Madia glomerata 
Marrubium vulgare 
Matricaria matricarioides 
Artemisia gnaphalodes 
Bromus brizaeformis 
Chenopodium botrys 
Chenopodium album 
Cirsium lanceolatum 
Collinsia tenella 
Polygonum aviculare 
Salsola kali tenutfolia 
Sanguisorba annua 
Sisymbrium altissimum 
Vaccaria vaccaria 
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 graecizgans 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 
