130 
W. B. Crump. 
Soil No. 13 (September, 1905). Vactinium Myrtillus and 
Deschampsia flexuosa growing in a shallow hollow on a Calluna 
Moor, Yorks. 
Air-dry Peat. Water 
Water at 15°C. Humus. Humus. 
i. Loose fibrous peat ins. 176'4% 78-8% 2-23 
ii. Compact peat ins. ... 6P0 17 4 3'52 
iii. Sandy “ sub-peat ” 1-2 ins. 2P1 S'l 2-59 
Rootlets penetrating ii. and entering iii. 
Soil No. 34 (March, 1906). Vactinium Myrtillus and Des¬ 
champsia flexuosa in Oak Wood (Q. sessiliflora), Yorks. 
Air-dry Peat. Water 
Wateratl5 ft C. Humus. Humus. 
i. Humus at 1-2^-ins. ... 170 0% 55'5% 3 06 
ii. Sandy soil below i. ... 304 10'4 2*92 
Rootlets permeating i. and extending into ii. 
Soil No. 66 (September, 1906). Nardus stricta on Nardus 
pasture, Yorks. 
Air-dry Peat. Water 
Wateratl5"C. Humus. Humus. 
i. Black soil at £-l| ins. ... 67-4% 33*4% 2-01 
ii. Same at l£-2^ ins. ... 40 3 18-6 2-16 
IV. —Water-Content a Function of the Humus-Content. 
In the first two soils it is clear that no significant result can be 
obtained by averaging such divergent values for the water-content 
as are revealed by the analyses. The cause for the divergence is 
not far to seek : it is found in the varying quantity of humus 
present in the different layers. If then the humus is the disturbing 
factor, it seems probable that if its influence can he eliminated the 
successive layers will not prove very different, and the real 
humidity—the state of wetness—of the habitat can he assessed. 
This is done by reducing the humus to unity in all cases. In other 
words the water-content is expressed in terms of the humus-content, 
water-content . 
and the ratio \ --—- which is used as the new index of the 
humus-content 
soil moisture may he fittingly called the coefficient of soil humidity. 
The importance of humus in increasing the water capacity of a 
soil has long been recognized. But the working hypothesis now 
formulated, is that the humus, as a colloid holds all, or practically 
all, the water in a humous soil, so that even with relatively small 
humus-contents the water holding power of the non-colloid consti- 
