OF A CAMBRIDGESHIRE WOODLAND. 345 
weight was obtained. The calcareous clay soils treated in this way show a 
percentage of organic matter varying from 15°9 to 6'9, giving an average 
over а large number of samples of. 10:97 per cent. The figures for the loam 
are rather lower—averaging 8:34, the maximum being 9:75 per cent. These 
averages correspond very closely with those quoted from Foreman above. 
These figures were obtained from soil samples taken below the surface, 
allowance being made for the decomposition of carbonates : the raw humus 
that aceumulates on the surface to the thickness of half an inch was not 
taken into account ; otherwise the figures for the loam would be much 
higher, about 14 per cent. 
The point in connection with the soil that so far has been most studied is 
the water-content, a point of extreme importance with regard to the 
vegetation * T. amples of soil for this purpose have been taken at 
intervals throughout the year : so far as was possible all samples were taken 
from those layers of soil in which the roots of the principal species spread. 
The usual method employed by agrieulturists of taking samples of 7 or 
inches ў depth does not give an adequate idea of the soil used by definite plants, 
The method employed to obtain the water-content was to heat the sample 
of soil in an oven at 100? C. till a constant weight was obtained. The 
sample on collection was placed in an air-tight tin and brought in and 
weighed in the laboratory as soon as possible after collection, and in all 
cases on the same day, to render the error by loss of water in transit as 
little as possible. 
Samples of soil dried by simply leaving them exposed at the temperature 
of an ordinary room, protected from dust, &e., take a very long time to dry, 
and, even when apparently so, always contain an appreciable quantity of 
water, varying with the atmospheric conditions. For this reason the oven 
method of drying was found more satisfactory as well as being very much 
quicker. 
The percentages of water are in all cases ealeulated on the dry weight ot 
the soil, and not, as often is the case, on the weight as collected. 
In connection with the water-content of soil, a feature that has been 
emphasised as of the greatest importance, especially in comparing different 
soils, is the water-holding capacity of the soil§ |. This was measured 
by the method suggested by Livingston || : the dry soil was placed in a 
vessel with a porous base and saturated with water, and then allowed to 
drain till water just ceased to come away in drops ; the amount of water then 
present gives the water-holding ‘apacity. . The calcareous clay has a water- 
holding capacity of about 46 per cent., while that of the loam js about 43, 
This is a factor which is of special importance in cases where the water-table 
* Warming, 1909, p. 47. T Clements, 1905, p. 25. 1 Hall, 1908, p. 48. 
$ Schimper, 1903, р. 84. | Livingston, 1910, p. 245. 
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