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had been laid bare quite recently and that there had not yet 
been time to form new aerial shoots from their lower parts. 
Yet another plant-species is seen on the larger dunes, 
some bushes of Populus euphratica, attaining the height of a 
man. This plant is a migrant from the river valley. Only a 
little group occurs at a single place where sheltered by one 
of the larger dunes. 
The deepest valleys among the dunes extend down to 
the loess-soil which is here perfectly naked. If any vegetation 
previously existed, it has been smothered by the sand which 
has only recently been blown off such valleys. 
Seen from the tops of the dunes, the loess-plain is not 
green, but is closely studded with green patches. On account 
of the neighbourhood of the river it is unusually thickly 
covered with vegetation. The following plants occur: low 
shrubs of Salsola subaphylla and S. Arbuscula, Alhagi and three 
annual species Ceratocarpus arenarius (thorny), Halanthium 
Lipskü and Salsola sogdiana (leaf-succulents). 
Places where there is sand are distinctly richer in vege- 
tation than the parts with pure clay. The first reason for 
this it that where the vegetation is more plentiful, the sand 
drifting along the plain becomes fixed. Thus hillocks of sand 
are drifted together here and there under the Salsola bushes, 
and the occurrence of e. g. Heliotropium is conditional on the 
presence of sand. 
Another and doubtless a more important reason is that 
the sandy soil affords more favourable conditions for vege- 
tation than the clay-soil. Some species are only found on 
these sandy soils, the most important being Tamarix which 
grows both on stationary stratified dunes and on loose sand. 
There is a tendency for the sand in dunes of this kind to 
form incrustations on the surface. Calligonum sp. (not frequent) 
and Heliotropium Radula are also present. 
Some of the species of the loess-plain are more frequent 
in occurrence and more strongly developed on sandy soil 
than on clay. With Alhagi this is mainly manifested by its 
bushes on the pure loess soil occurring as a rule singly, 
while on the sandy soil many were grouped together. This 
is doubtless due to the fact that the Jong horizontal roots 
9 
