— 123 - 



of the fine sand has grains less than 0,5 mm and some of 

 this is smaller than 0,25 mm. The greater mass of the coai'se 

 sand is between 1 and 0,6 mm in diameter. 



The larger dunes here are very long, but comparatively 

 low (2 about to 3 metres) narrow, and crescent-shaped. Their 

 direction is about NNE — SSW, with their lee sides towards 

 ESE; they must consequently have been formed by winds 

 from WNW. The soil between the dunes is sandy also, no 

 clay is visible. 



No vegetation is found as a rule on the dunes them- 

 selves. Aristida pennata is rather common, but it does not 

 grow, or only rarely, on the most shifting, crested dunes. Al- 

 hagi Camelorum and the other herbaceous plants prefer still 

 calmer places. Nor do the switch-shrubs occur frequently on 

 the shifting sand; of these Eremosparton aphyllum, Ammoden- 

 dron sp., Smirnowia turkestana, are found as low bushes which 

 may attain a height of about a metre. Ammodendron is here 

 very thorny {A. Siewersii?). The shrubs are very broad, some 

 measuring about 1 metre in diameter. One had become tree- 

 like through the lower branches on the stem having been 

 killed by some previous sand-drift. 



The most common plant in the desert here is Convolvu- 

 lus erinaceus (see p. 94), which at this season shows numerous 

 small pink blossoms. It is plentiful everywhere except in the 

 deeper valleys and on the tops of the dunes. Its form is a 

 leafless, thorny ball. The roots are white and very long. The 

 sand has been blown away from many of the plants so 

 that they look like small trees with stems which are in real- 

 ity the upper rootstocks. If still more sand is blown away, 

 the plant falls prostrate on the ground. Thus roots over a 

 metre long can be found lying on the surface of the sand 

 fixed at one end only, and still having small green shoots. 



Uncovered vertical stems of Alhagi are also seen, dead 

 at the end and with new aerial shoots springing from the 

 lower, previously buried parts; also buried specimens which 

 have formed new aerial shoots from the axillary buds of the 

 upper leaves. 



Heliotropium Radula (?) is also common, growing in the 

 way already described (see figs. 22, 63). There are rhizomes 



