The Co-Efficient of Humidity. 133 
is towards the end of a two or three weeks’ drought, and this can 
often he done in April, or June, or onwards to September. 
Local Soil Variation. Samples to all appearance identical 
either from the same section, or from adjacent spots always show 
some, and often considerable variation in water-content. These 
accidental errors are entirely eliminated by the use of the coefficient 
of humidity. With this point in view the following samples of 
woodland soils, each to all appearance uniform, were divided and 
analysed separately. Their uniformity is confirmed by the results. 
Frequently when the samples are not as carefully chosen there is a 
more marked disparity in the water-content. 
Ground Societies in Oak Wood on Coal Measures, Yorks., 
February, 1912. 
Air-dry Soil. Water. 
No. 
Society. 
Water at 15° 
Humus. 
Humus. 
193. 
Scilla non-scripta (a) ... 
24-4% 
6-9% 
3-5 
03 ) — 
30-5 
9-3 
3-25 
194. 
Carex pendula 
(a) ... 
281-2 
30-3 
9-3 
03 ) — 
- 248-3 
26-7 
9-28 
195. 
Spircea Ulmaria 
(a)... 
92-3 
23-1 
4-0 
( 13 )... 
90-0 
22-0 
4-08 
197. 
Holctis mollis 
(a) ... 
31-2 
12-9 
2-4 
(/?)... 
28-6 
12-1 
2-36 
The Moor Formation. A brief statement is all that is necessary, 
as it has been already shown that the various types of moorland on 
the Pennines are readily distinguished by the water coefficient of 
the peat. 1 On the Eriophorum moor, for example, its value generally 
ranges between five and seven though it may touch eight when the 
peat is composed of Sphagnum. An even higher value has been found 
on the lowland mosses of Lonsdale where the dominancy of Erio¬ 
phorum vaginatum is disputed by Scirpus ccespitosus. Pools choked 
with living Sphagnum are of frequent occurrence and the peat 
is at times more than saturated with water so that the coefficient 
here attains its highest possible value. This has been confirmed 
experimentally, for when the peat has been saturated with water in 
the laboratory, its maximum water capacity has been found to be 
identical with its water-content in situ. What an enormous 
difference can be brought about by even partial drainage of the 
habitat is illustrated by a comparison of the two analyses below 
showing (1) the superficial layer possessed by Calluna and (2) the 
' Crump, W. B. “The Water Content of Acidic Peats.” Report of the 
British Association, Portsmouth Meeting, 1911 ; Naturalist, 1911, pp. 361-2, 
