INFILTRATION OF WATER. A475 
paving the ground about the stems of vines and trees. The 
surface-earth around the trunk of a tree may be made almost 
impervious to water, by flagstones and cement, for a distance as 
great as the spread of the roots ; and yet the tree will not suffer 
for want of moisture, except in droughts severe enough sensibly 
to affect the supply in deep wells and springs. Both forest and 
fruit trees attain a considerable age and size in cities where the 
streets and courts are closely paved, and where even the lateral 
access of water to the roots is more or less obstructed by deep 
cellars and foundation walls. The deep-lying veins and sheets 
of water, supplied by infiltration from often comparatively 
distant sources, send up moisture by capillary attraction, and the 
pavement prevents the soil beneath it from losing its humidity by 
evaporation. Hence, city-grown trees find moisture enough for 
their roots, and though plagued with smoke and dust, often 
retain their freshness, while those planted in the open fields, 
where sun and wind dry up the soil faster than the subterranean 
fountains can water it, are withering from drought.* Without 
the help of artificial conduit or of water-carrier, the Thames 
and the Seine refresh the ornamental trees that shade the 
thoroughfares of London and of Paris, and beneath the hot and 
reeking mould of Egypt, the Nile sends currents to the ex- 
tremest border of its valley. 
* The roots of trees planted in towns do not depend exclusively on infiltra- 
tion for their supply of water, for they receive a certain amount of both mois- 
ture and air through the interstices between the paving-stones; but where 
wide surfaces of streets and courts are paved with air and water tight asphal- 
tum, as in Paris, trees suffer from the diminished supply of these necessary 
elements. 
+ See the interesting observations of KRIEGK on this subject, Schriften zur 
allgemeinen Erdkunde, cap. iii., § 6, and especially the passages in RITTER’S 
Erdkunde, vol. i., there referred to. 
The tenacity with which the parched soil of Egypt retains the supply of 
moisture it receives from the Nile is well illustrated by observations of Girard 
cited by Lombardini from the Mémoires de ? Académie des Sciences, t. ii., 1817. 
Girard dug wells at distances of 3,200, 1,800, and 1,200 métres from the Nile, and 
after three months of low water in the river, found water in the most remote 
well, at 4m, $7, in the next at 4m, 23, and in that nearest the bank at 3m, 44 
