Southeastern Washington and Adjacent Idaho. 25 
But the soil water reached its non-available point somewhat ear- 
lier. However, the Agropyron consociation was the first to ex- 
haust its available supply. 
The enormous strain brought to bear upon these early develop- 
mental plant communities may be realized when it is noted that 
after the water of the first 10 inches of soil became unavailable, 
the evaporation throughout the remainder of the season was very 
high. Two methods of meeting these adverse conditions are em- 
ployed by plants of these communities. They either mature early 
and become dormant upon the approach of drought, or develop 
very extensive root-systems. But these had best be discussed 
under structure and development of vegetation. 
The mechanical analyses of these soils show that those of the 
Agropyron consociation are of a coarser texture than those of 
the Festuca consociation (Table II). Likewise the humus and 
volatile matter were found to be lower in the former. 
TABLE {1 
MECHANICAL ANALYSES OF SOILS FROM VARIOUS PLANT COMMUNITIES IN 
SOUTHEASTERN WASHINGTON AND ADJACENT IDAHO 
Gravel gre Qand*| dium | Sang | Fine | Site | Clay 
Station Ove | 2.00 | x.00 | Sand 0.25 Sand 2:95 S25 
ae to r.u0|to 0.50}, 9-59 |to 0.10} 97° OE 005 ee 
m Mm Mn. |t° 9.25] Mm. | t9 0-05 m, m. 
= : m. Mm. 
Agropyron consociation, Col- 
IGE Ca oA Sas, ol a Ea Ee ah Hotels (Ske On OOM EGO" | 3A4.4 6) | SA.20) | (47204: 
Festuca consociation, Colfax! ....|....| .80]| .40] .40 | 23.30 | 66.00 | 9.00 
Festuca consociation, Ka- 
PEATE eS ek ah oat iy a ee .68 | .40| 1.40 | .42 | 5.80 | 26.80 | 54.10 | 10.83 
Pseudotsuga-Larix commu- 
Rit icaAmnak IMGs 5s 2) 2 ZOOn ew aie) sel 2) | 400) Tayeal 2t.000 100 SOn| Asaa 
Thuja consociation, Cedar 
INTC EATING 2 ener c cote hel anovar 6.08 | .62 | 3.60 | I.60 | 3.60 | 21.65 | 57.60 | 5.70 
Pseudotsuga-Larix-A bies 
community, Cedar Moun- 
CAs ote saree oe 3-56 | 1.04 | 1.52 | 1.08 | 7.82 | 25.37 | 55.40 | 4.18 
Festuca consociation, North- 
east slope, Pullman...... Tie 40 | .40] .90 | 1.50 | 33.16 | 53.50 | 10.03 
Festuca consociation, South- | 
west slope, Pullman...... Coal pendee 60 .60 .40 | 23.58 | 73.30 I.49 
