NT) 
are mostly found in the northwestern part of the lowland. 
They are comparatively well covered with switch-like desert- 
shrubs, Carex physodes, etc., and the sand-drift is of no great 
importance. 
5. “Dunes”, or recent accumulations of shifting greyish 
or white sea-sand occurring mostly along the coast of the 
Caspian, and generally arranged in chains which follow the 
direction of the wind. 
Dune-chain sands and recent dunes, both formed by 
white or grey sea-sand, | have not seen, hence they are here 
left out of consideration, and only the different forms of 
inland-sand are dealt with. 
The first point to be considered is sand as a soil for plants 
in comparison with clay. 
In dry countries sand is, in some respects, more favour- 
able to vegetation than clay.') Water is quickly absorbed so 
that it has no time to evaporate. Less water will evaporate 
from a rough, coarse-grained surface of sand than from an 
even, fine-grained surface of clay. Because of the slight water- 
holding capacity of sand, the water is carried to greater depths, 
whence it does not rise easily to the surface owing to the 
poor capillarity of sand. The evaporation-surface of the water 
will therefore be situated down in the earth where it is pro- 
tected by the overlying drier layers of soil (comp. LIVINGSTON 
1906). Deep sand is a soil which suits plants with very long 
roots. The switch-shaped trees and shrubs generally occur 
here. 
Though sand can absorb much less water than clay 
(14,3 per ct. of dry weight, loess 59,3 per ct. according to 
CLEMENTS, p. 34), almost all the water absorbed is available 
for the plants: “Echard” is only 0,3 per ct., “Chresard” 14 
per ct. (comp. above p. 58). The figures vary of course some- 
what according to the properties of the sand, especially the 
size of the grains (Livingston 1905), but I am not aware 
‘) Fitting (p. 251) also finds that the sand-plants of the Sahara have 
a lower osmotic pressure than the plants of the stone-deserts even when 
they belong to the same species. 
