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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 

 Lipskii 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 long horizontal roots 



