THE SOILS OF THE DESERT LABORATORY DOMAIN.? 

INTRODUCTION. 
The present study of the main soil types of the Desert Laboratory 
domain is to be considered as only preliminary, but may be of value 
pending the accumulation of data for a more thorough treatment of the 
subject. In this paper will be presented a brief description of the four 
most distinct types of soils, together with data on their water capacity, 
and some discussion of the moisture conditions which normally obtain 
in them. Data regarding the fluctuations in water-content in these soils 
will be given for the period from October 3, 1907, to April 11, 1908. 
The importance of soil conditions to plant development, a subject 
which has received but slight attention in a scientific sense, even from 
students of distribution, is hardly to be overestimated. It is from the 
soil that terrestrial plants derive their water-supply as well as their supply 
of mineral salts, and therefore the root-system of the plant is perhaps 
more fundamentally important in determining the vital activities of the 
latter than the better known, because more thoroughly studied, subaerial 
portions. The normal functioning of the root-systems, as far as fur- 
nishing water and salts to the entire plant is concerned, is directly depend- 
ent upon the-saline and water contents of the soil. The development 
of a normal root-system, and hence its very existence, depends not only 
upon these conditions, but also upon the supply of oxygen which is main- 
tained in the soil; the oxygen of root-respiration must be derived mainly 
from the substratum in which the roots lie, and not to any marked extent 
by diffusion through the plant-body from the air above. The permea- 
bility of a soil to air is dependent, in a general way, upon properties of 
the soil itself, e. g., upon its porosity or size of particles, but is probably 
dependent even more definitely, in many instances at least, upon its 
water-content. This consideration is of peculiar importance in arid 
regions, where many native plants appear to require a well aerated soil 
for their normal development, and to become unhealthy if the moisture 
content rises too high. The distribution of plant forms is perhaps more 
often determined by availability of oxygen than by that of water. This 
is-a subject, however, in regard to which we have at present almost no 
- definite knowledge. 
In certain rather restricted areas, especially in the arid regions, the 
character of the vegetational cover is dependent upon the soluble content 
of the soil, in a manner quite different from that mentioned above. In 
these cases (of ‘‘alkali” soils) the available water-content is often deter- 
mined, not by the physical nature of the soil itself, but by that of the 
1This section, pages 83-94, was prepared by request and contributed by Dr. B. E. 
Livingston, Member of Staff of Desert Laboratory. 
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