Vol. I, No. $ 
392 Journal of Agricultural Research 
The conclusion seems warranted that the presence of the Kochia 
association to the exclusion of sagebrush is determined by the occurrence 
of 1 or at most 2 feet of soil free from an excess of salts, underlain by a 
subsoil which is strongly saline or which for some other reason is un¬ 
favorable to deep penetration of roots. 
Summary or Physical Conditions. —In Tooele Valley the land occu¬ 
pied by the Kochia association is distinguished from that occupied by 
the sagebrush association by its finer texture, its tendency to puddle at 
the surface and, hence, resist the penetration of water, and its higher 
moisture-holding capacity, and also by the limitation of the depth in 
which the roots can freely develop to not more than 24 inches, the 
obstacle to deeper penetration being usually the high salt content of the 
subsoil. 
Adaptations to Physical Conditions 
Since Kochia vestita is the only very important species of the Kochia 
association, the structure of this plant alone need be considered in its 
Rig. 7 .—Kochia vestita: A, Detail, showing the narrow, hairy leaves; B, a plant showing the shallow root 
system and the propagation by root shoots. 
relations to the physical conditions. The underground portion of the 
plant (fig. 7) is well adapted to the comparatively small depth of soil 
from which the total supply of water must be obtained. Kochia vestita 
spreads by means of long, slender-branching root shoots, which extend 
almost horizontally for distances of 10 feet or more, and often at a depth 
of only 3 inches from the surface of the soil. At intervals clusters of 
vertical shoots are sent up, and, hence, the plants above ground appear as 
isolated, unconnected clumps. In typical portions of this association the 
feeding roots are limited to the first 12 to 18 inches of the soil, the depth 
which is usually free from excessive quantities of alkali salts. 
At one point where the root distribution was studied with special care, 
living roots were traced to a depth of about 18 inches, and at that depth 
the soil contained 0.9 per cent of salts, while at a depth of about 21 
inches there was 1.6 per cent. Below this depth traces of dead roots 
were observed. Excavation at another point, where the first 6 inches 
