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summer-aspect; then in its spring-aspect, which greatly re- 

 minds one of that of the clay-desert. 



In tlie more shifting deserts tliere are areas witli notliing 

 of interest to the botanist. Hills and valleys of sand, not 

 even a stone, nothing but sand. This is sorted out by the 

 wind, the coarser and darker sand covers the gentle slopes 

 of the windward side and the crests of the wind-billows, 

 while the finer and lighter sand is found on the steeper lee 

 side and in the valleys. These variations in shade increase 

 the relief of the surface. 



The first pioneer of the vegetation is "Selin", Aristida 

 pennata Trin.'), so aptly called by Antonow the Conqueror 

 of the Sand-desert. 



Aristida pennata takes first place as a sand fighter. It 

 grows quickly, and gives off many roots, many leaves, manj' 

 branches, while its internal structure enables it to endure 

 drought and sand-drift. It is more fully described later 

 (chap. 13), but features of its biology may be indicated now. 



After germination it forms a number of basal scale-leaves 

 through whose sheaths the fibrous roots break out. The foli- 

 age leaves follow on short internodes so that their sheaths 

 form a "Tunic" (Hackel), the one sheath lies over the other, 

 with only a short apex free, so that the expanded leaf-blades 

 are close-set one over another. In the axils of the scale-leaves 

 lateral shoots quickly appear covered by their "tunics". The 

 young plant thixs forms a close tuft with the oldest shoots 

 in the middle (fig. 9), and as the tufts grow older they be- 

 come coarse leafy tussocks half a metre or more in diameter. 

 When the sand drifts over, the plant pushes upwards with 

 longer internodes, and new lateral shoots with basal roots 

 are continually being formed, so that the plant is fixed in 

 the sand almost right up to the surface. The lateral shoots 



') This plant has been named at different times A. pungens Desf., 

 A. pungens var. pennata, A. pennata and sometimes it has been regarded as 

 two species A. pennata and A. pungens. It is certainly closely related to 

 the Sahara form A, pungens, being distinguished from it mainly by its more 

 slender growth and by longer branches of the panicle. 1 do not think there 

 is any reason for calling specimens with shorter panicle-branches A. pungens. 

 The Transcaspian specimens are certainly all the same species 



6 



