86 
A. G. Tans ley. 
not decreased by the high salt-content; and this is in line with 
most of the modern work on the physiology of halophytes. Suceda 
Moquinii , another marked halophyte, forms societies in this 
association. 
The secondary species are much the same throughout this 
series of associations— Chrysothamnus graveolens and Gutierrezia 
Sarotlircc being the most conspicuous species. 
(5). We now come to the salt flat association, dominated by 
Allenrolfea occidentalis (a Salicornia- like plant with alternate instead 
of opposite leaves) or alternatively by the grass Distichlis spicata 
or by Salicornia Utahensis. In this association the high salt-content 
(1 to T25%) which is present at the greater depths under associations 
(2) to (4), extends to the surface foot of soil, the water table is much 
higher, and there is available water at all depths during the whole 
year. The association extends to the edge of the lake and consists 
of extensive mud flats covered in summer with a glistening white 
crust of salt and broken by low ridges and hummocks. The 
vegetation is of an open type. 
There is another association strongly irrigated by springs, etc., 
which has been called the marsh mixed association. It is less 
saline than (4) and (5) and contains a more varied flora including 
Sporobolns airoides, Juncus balticus, etc. This is dependent on 
local irrigation and does not form part of the series described above. 
There is probably no case in which the physical factors 
determining the occurrence of a series of associations have been 
worked out so satisfactorily and completely as in these associations 
of Tooele valley, which appear to be typical of a large part of the 
Salt Lake basin. 
Where the land is irrigated good crops are raised, and the 
Lombardy poplars are specially fine. 
Arid Regions of the Snake and Columbia River Basins. 
About midnight the party left Salt Lake City by the Oregon 
Short Line, and the next two days were spent mainly in the train, 
traversing the states of Idaho, north-eastern Oregon and Washington. 
During the whole of August 25th the train traversed sage-brush 
desert in the Snake River valley (Idaho) from Pocatello (Idaho) to 
Huntingdon just over the Oregon State line, which was reached in 
the evening. The monotonous grey sage-brush association with 
occasional patches of grass ( Agropyron , etc.) and here and there 
the bright yellow-flowered Chrysothamnus, was broken only by 
