'IRAQ AND THE PERSIAN GULF' [‎134v] (273/862)

l86 CLIMATE, VEGETATION, AND FAUNA
rain in the year, while at Samawa near the rice-growing area of the
Euphrates, rainfall drops to 3 inches or less. In the Wadiyan
district conditions are even more severe, and the occasional local
rain may leave some areas untouched for years. Dews, however, are
sometimes very heavy and supplement, to some extent, the exiguous
rainfall.
The monotonous undulating plains of the Wadiyan are broken up
by a complicated system of wadis which run in the general direction
of the Euphrates, though few reach it (fig. 30). Since there is no peren
nial stream in the area, no hydrophytic vegetation is found west of
the Euphrates; but, in addition to the wadis, the banks of which are
sometimes quite deep, numerous other shallow depressions and
gullies collect the limited rainfall. It is in these depressions, where
drainage is poor, that salt-marshes (sabkhas) develop under the in
tense heat of the sun. Such spots are frequently the centres of halo-
phytic communities of plants, the components of which are able to
withstand extreme saline conditions.
As in most arid or semi-arid countries, the humus content of the soil
is low or non-existent. This is caused both by the paucity of the
plant cover and by the high soil temperatures. The result is that the
power of retaining water, which humus confers on a soil, is lacking,
except where clay is present. On the rare occasions when rain falls,
the water sinks through the soil or drains off rapidly to lower levels,
and consequently the richest plant communities are found in hollows
and depressions where the subsoil water is again near the surface of
the ground so that the soil remains moist for longer periods. These
wadis and depressions are frequently the only areas of plant life in
immense barren stretches, and their location is the basis of beduin
existence in the desert.
Vegetation. Our knowledge of the vegetation of the Syrian desert is
scanty and is limited mainly to such areas as are easy of access or to
the observations of travellers and explorers, such as Alois Musil.
Much of the extensive Hajara and Dibdibba districts in the south
is still largely a terra incognita to botanists.
In the driest parts of the desert there are extensive rocky and
gravelly plains of almost complete sterility. In the Wadiyan district,
for example, at the end of March, Musil speaks of‘long wide plains
where there was not a plant’, and writes, ‘everything around us was
ashen-grey; the upland was absolutely desolate, dead, while in the
lower places appeared only the dry lifeless bushes of Salsola lanci-
folia, wormwood, or Astragalus spinosus\ In stony gullies he noted