1905] LIVINGSTON—RELATION OF SOILS TO VEGETATION 25 
Especially is this true in the case of humus, which is composed of 
organic débris, decayed plant parts, and to some extent of animal 
offal. Pure humus has a great power to hold and lift water. This 
is partly because of its very fine particles, but is also to be traced in 
part to the actual penetration (by imbibition) of the liquid into the 
intermolecular spaces of the organic substance itself. Thus, by 
admixture of humus to a coarse (and therefore porous and permeable) 
~ soil, the water capacity of such a soil is increased. The filtering 
' power or permeability to water of a soil increases of course with 
| _ decrease in its capillary power. Also its permeability to air increases 
» in the same way. 
4 A general exposition of this question of size of particles, water- 
retaining power, etc., is to be found in either of the works just cited. 
A much better treatment, however, has appeared in the publications 
of Briccs5 and WuitNneEy.° The reader is referred especially to the 
writings of the former author. 
Chemical analyses of a number of Michigan soils have been made 
and published by Kepzie.7_ Table I, showing chemical constituents 
_ and water capacity, is compiled from his pages, the samples described 
| being all from the portion of the state in which the present studies 
_ were made. The first column gives the chemicals found in the soil, 
in per cent. of dry weight, excepting in the case of water capacity, 
which is presumably given in per cent. of total volume—although 
this is not stated in the original papers. The upper tier gives the 
_kind of soil, the location, and the nature of the forest cover. 
: 
5 Briccs, L. J., The mechanics of soil moisture. U.S. Dept. Agric., Div. Soils, 
Bull. ro. 1897. 
——., Investigations on the physical properties of soils. U. S. Dept. Agric., 
Field operations Div. Soils, 1g00-1901. pp. 418-421. 
6WuitneEY, M., The Division of Soils. Yearbook U.S. Dept. Agric. 1897. pp. 
120-125. 
, Soil moisture. U.S. Dept. Agric., Div. Soils, Bull. 9. 1897. 
see WHITNEY, M., and CAMERON, F. e chemistry of the soil as related 
to crop-production. U.S.’Dept. Agric. Bull, 22. ak 
7 Kepzir, R. C., The jack pine plains. Mich. Agric. Exp. Sta., Bull. 37. Also, 
27th Ann. be Secy. State Bd. Agric. 1888. pp. 207-210. 
of Michigan, Bull. 99. Also, 52d Ann. Rept. Secy. State Bd. 
Agric. ae PP: 403-415. 
