322 On the Rain and Drainage - Waters at Rothamsted. 
With a rainfall of 25 inches, the drainage would in like manner 
be 30 per cent. With a rainfall of 20 inches, 12'5 per cent. 
It must be carefully borne in mind that the whole of the facts 
and figures hitherto given relating to drainage and evaporation 
have reference to a soil entirely bare of vegetation, and con- 
sequently are only partially applicable to ordinary land which 
is always more or less covered with vegetable growth. 
We have now gone through the principal facts which the 
amounts of percolation from the three drain-gauges appear to 
teach. That experiments with soils kept bare of vegetation can 
only touch a part of the questions connected with practical 
agriculture is most true. A series of percolation experiments 
in which the influence both of crop and manure on the amount 
and composition of the drainage-water might be studied, was 
planned many years ago, but has not been brought to a suc- 
cessful issue. Eighteen cylinders made of stone-ware pottery, 
each 5 feet in depth and 2 feet in diameter, were sunk in the 
ground nearly to their upper edge. It was intended that these 
cylinders should be filled with soil similar in kind to that 
forming the three drain-gauges. Crops would then have been 
grown, and manures applied, the drainage-water passing 
through the soil collected and measured, and its composition 
determined by analysis. The substances applied as manure, 
and removed in the crop and drainage-water, being thus known, 
it was hoped that valuable information would be obtained on 
many important questions. Unfortunately the cylinders were 
found to leak. It also proved impossible to get into them the 
amount of soil necessary to obtain the same degree of con- 
solidation as that occurring in a natural field, although much 
water was poured through, and a pressure exceeding one ton was 
in some cases applied. No further steps have yet been taken. 
Several investigations have been made at Rothamsted on the 
subject of the evaporation of water by plants, both when grown 
in pots * and in the field. In a paper published in this 
'Journal' in 1871 (page 91), calculations are given as to the 
amount of water removed from the soil by certain crops during 
the hot and dry summer of 1870, the calculations being based 
on actual determinations of the amount of water remaining 
in the soil after the removal of the crops. Thus it was shown 
that a crop of manured hay of 29i cwts. had removed from the 
soil at least 2 inches, and another manured crop of 56j cwts. at 
least 3'2 inches more water than an unmanured crop of 5f cwts. 
In the case of a crop of barley grown on the same field in which 
the drain-gauges were afterwards established, the crop had appa- 
* '' Experimental Investigation into the Amount of Water given off by Plants 
during their Growth, especially in relation to the fixation and source of their 
various constituents.'' —Jour. Hort. Soc. Lend. v. 38, 1850. 
