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of the plant in the summer, and prevents those bad 
effects that often happen in lands in their natural 
state, from a long continuance of dry weather. 
When the water used in irrigation has flowed 
over a calcareous country, it is generally found im- 
pregnated with carbonate of lime ; and in this state 
it tends, in many instances, to ameliorate the soil. 
Common river- water also generally contains a 
certain portion of organisable matter, which is much 
greater after rains, than at other times ; and which 
exists in the largest quantity when the stream rises 
in a cultivated country. 
Even in cases when the water used for flooding 
is pure, and free from animal or vegetable sub- 
stances, it acts by causing the more equable diffu- 
sion of nutritive matter existing in the land ; and 
in very cold seasons it preserves the tender roots 
and leaves of the grass from being affected by frost. 
Water is of greater specific gravity at 42° Fah- 
renheit, than at 32°, the freezing point ; and hence 
in a meadow irrigated in winter, the water imme- 
diately in contact with the grass is rarely below 
40°, a degree of temperature not at all prejudicial 
to the living organs of plants. 
In 1804, in the month of March, I examined the 
temperature in a water meadow near Hungerford, 
in Berkshire, by a very delicate thermometer. The 
temperature of the air at seven in the morning was 
$9°* The water was frozen above the grass. The 
temperature of the soil below the water in which 
the roots of the grass were fixed, was 43°. 
In general those waters which breed the best fish 
