1919. ] Seistan and the Helmand. 9 
further among the reeds. The bottom is covered with a thin 
layer of peaty material, below which it is malodorous and black. 
It is as arule from four to seven feet deep in the winter season, 
The channels widen out at intervals into open pools of two sorts, 
the larger of which are devoid of phanerogamic plants. Those of 
the smaller sort, which are rarely more than about six to ten yards 
wide, are rather deeper than the channels and are blocked with 
aquatic vegetation. ‘This consists mainly of Potamogeton pectina- 
tus, which with its narrow, grass-like leaves forms fairly dense 
masses from the bottom to the surface. Interspersed with it are 
single plants of P. ferfoliatus, Natas major and Characeae. In 
the channels themselves single plants of P.lucens and at some 
places rather more densely congregated plants of Vallisneria 
spiralis form the only phanerogamic vegetation apart from the 
reeds. 
The reeds act in all the channels and pools as a very effective 
wind-screen, so that even when a blizzard is blowing outside there 
is calm in the reed-beds. They also protect the water to some 
extent from frost. 
_ Immediately outside the reed-beds, towards the open lake, 
there are at some places beds of Potamogeton perfoliatus, but the 
bottom of this part of the lake is usually bare. In calm weather 
the water is clear, but calm is exceptional in Seistan and as a rule 
it is turbid and of a milky appearance. 
All the subaqueous plants of the Hamun are in a more or less 
moribund state in winter, the Vallisneria and Potamogeton pectina- 
tus less so than the rest. Of the other species we found only occa- 
sional living shoots. 
In the southern part of the Hamun-iSabari we made no 
sounding greater than 73 feet, but rather deeper pockets are said 
to exist further north. It will be remembered, moreover, that our 
visit took place at the season at which the lake is almost at its 
lowest. 
From a biological point of view the periodic and occasional 
changes in the level of the lake are of great importance. These 
are produced mainly by two causes, evaporation and changes in 
the supply from the Helmand due chiefly to the rate of melting 
of the snows of the Hindu Kush. The direction of the wind is 
so constant that its effects need not be considered. When it 
ceases to blow the water retreats a little but the result is quite 
temporary. In the year 1885, in which the Hamun was unusually 
full, the water reached its maximum in April, remained at its 
highest level up to the end of May and sank alittle over three feet 
between that month and December. 
In a climate like that of Seistan the loss of water by evapora- 
tion is very considerable in summer-time. The actual rate of 
evaporation apparently differs in different parts of the country in 
correlation with differences in the chemical composition of the 
water, being in the Gaud-i-Zirreh half of what it is in pools in the 
northern parts of Seistan. The whole question, however, is very 
