36 



the soil but results rather from the dryness of the atmosphere, 

 especially the strongly heated lower layers of the air, com- 

 bined with the direct effect of the sun's rays, and the reflec- 

 tion of these from the hot bare yellowish-grey sandy soil." 



KORSHINSKY regards the vegetation of ligneous plants des- 

 cribed above as specially characteristic for the sand-desert, 

 and he is also of opinion that this is the original vegetation 

 which formerly covered the whole area of sand. The change 

 from fixed to moving sands is, he thinks, due mainly, perhaps 

 exclusively, to the action of man. As soon as roads and 

 inhabited places are left behind, we find the sands more 

 level and covered with the trees and shrubs just named. The 

 nomads are mainly responsible for the extermination of trees 

 and bushes, as they cut them down for firewood and their 

 cattle eat and tread down the vegetation. As it is now w r e 

 find perfectly lifeless areas, occupied by the high, crescent- 

 shaped "Barchans" devoid of plants. The transition to this 

 is seen in the stage where most of the herbaceous plants 

 have disappeared, and isolated trees and bushes occur with 

 Aristida pennata and A. pungens still holding their ground. 



Even in the barren desert, some vegetation may still 

 be found in places where water from melting snows or river 

 floods has collected in the hollows and deposited finer par- 

 ticles of earth which bind the sand together. In addition to 

 numerous typical sand-plants, many of the more showy herbs 

 grow here such as Ceratocephalus falcatus, Euclidium syriacum, 

 Umbelli ferae, Koelpinia linearis and many others; KORSHINSKY 

 (p. 7) gives a long list of them. 



A further step in this direction in seen in the "Takyr", 

 flats or depressions covered by water after rain. The water 

 evaporates rapidly leaving a greasy soil, which when dry 

 becomes very hard and cracks, salts frequently crystallising 

 out. "Takyr" are almost always devoid of plants. 



At the foot of Kopet-Dagh lies a narrow strip of cul- 

 tivated land which towards the north is bordered by the 

 desert. It is watered by streams coming from the mountains, 

 but they are few in number and carry little water, so that 

 large patches are left uncultivated among the fields In these 

 uncultivated parts the desert plants are mixed with weeds of 



