142 BULLETIN 1059, U. S. DEPARTMENT OF AGRICULTURE. 
drought while the other thrives. Unless, then, it is desired to deal 
in generalities, and ascribe to one species certain characters which, 
another does not possess, on the basis of general knowledge or pure 
assumption, it will be necessary in studying competition to go to the 
whole leng-th prescribed for the determination of the coefficient of 
availability. 
16. Much the same situation exists with respect to the study of the 
final character of the forest formation, its height, rate of growth, 
etc. The critical study of the moisture conditions in relation to 
ultimate height is of special importance in forestry because ultimate 
height, in forest management plans, is often taken as a criterion of 
the quality of the site; that is, its yield possibilities. Are the two 
things closely related? If the ultimate height is limited by drought 
conditions which occur only periodically, may not the yield possi- 
bilities be considerably greater or less than would be indicated by 
this measure, depending very much on the total water-holding 
capacity of the soil, etc.? Obviously such questions as these can be 
answered only after exhaustive study. This requires the establish- 
ment of permanent soil-moisture stations, the determination each 
year of the critical conditions that exist, and the use of the entire 
system that has been suggested for arriving at a measure of the true 
conditions. 
Special Equipment for Soil Moisture and Soil Quality Study. 
Soil sieves : 
Standard soil sieves. Per set, about $10.00 
Soil borers : 
3-foot soil borer, tube, with hammer.! 9. 00 
6-foot soil borer, tube, with hammer 11. 00 
6-foot soil borer, auger handle hammer . 12.00 
Soil cans: 
Patent seamless, noncorrosive, tin soil cans — 
4-ounce can, deep style, per gross 3. 50 
8-ounce can, deep style, per gross ' 4. 00 
(35 per cent discount on above prices to United States 
Government. ) 
Soil sample cans, seamless tin, No. 9178 A— - 
Capacity, ounces 4 8 16 
. Per dozen $0. 22 $0. 33 ' $0. 55 
Soil sample cans, aluminum, with screw tops — 
2\ inches in diameter by 1\ inches high, unnumbered 9183, 
each . 25 
With can cover numbered. (In ordering, state what numbers 
are desired.) No. 9183 A, each .30 
Soil sample can, aluminum, with aluminum top. The diameter of 
these cans is uniform, so that the cover fits the bottom of the can, 
