41 



sand has been carried away, the roots are covered in with 

 sand over which a layer of clay is spread. On an average 

 about half the plants are successful, but the gaps are filled 

 up by a second planting. 



It is of the greatest importance for the natural seeding 

 of trees and bushes that many herbaceous plants should 

 grow on the sand; if these are absent, then many seeds of 

 Aristida pennata and Alhagi Camelorum are sown. The herb- 

 aceous plants retain the fruits of the trees and protect the 

 seedlings during their growth. 



We have here only referred to those parts of PALEZKIJ'S 

 work which deal with the vegetation. 



G. J. TANFILJEW in the second Russian edition of WAR- 

 MING'S "Plantesamfund" (Oecology of Plants) (translated by 

 GENKEL, St. Petersburg 1903) gives a survey of the vegetation 

 of Russia. The chapter dealing with deserts is of special 

 interest to us. Desert and Steppe are closely related in the 

 following respects: both are at the present time devoid of 

 trees, they are not leached by running water and the soil is 

 rich in dissolved salts, especially carbonates but also sul- 

 phates and chlorides. 



In the steppe, however, carbonate of lime is dominant, 

 and the more soluble salts do not attain the same concen- 

 tration as in the desert. The steppe-vegetation is therefore 

 richer, forming a more or less thick carpet all the year round, 

 and the decomposing vegetable matter gives a dark colour 

 to the upper layers of the soil (for instance in the Tjernosem). 

 In the deserts the carpet of vegetation is either absent alto- 

 gether or is present only in early spring; during summer and 

 autumn the earth is bare or only sparsely covered with 

 woody stems or dead shoots. No green-sward is present and 

 no dark humus is formed, but dissolved salts are abundant 

 and often crystallize out on the surface. 



The Semi-Desert (Loess desert) is related to both steppe 

 and desert. It resembles the desert in that it lacks the dark 

 surface-layer of humus and the perennial sward of plants, 

 while it has the high salinity of the loess. On the other 

 hand, the luxuriant spring-vegetation is like the steppe, the 

 loess of which is identical with that of the semi-desert. 



