RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 81 
lack of water in the aerial portions. This is particularly true of 
yellow pine and Douglas fir seedlings, at the age of six weeks or more, 
while lodgepole pine does not harden until much later. 
For these reasons wilting can rarely be recorded in a large num- 
ber of seedlings simultaneously, and it is therefore desirable that 
the moisture content should be recorded as each seedling wilts, an 
algebraic mean content being computed when the process is complete. 
While Briggs and Shantz found it desirable to grow the seedlings 
in small glass pots (these seem to have had about the dimensions of 
drinking glasses), the heterogeneous character of nearly all forest 
soils necessitates the treatment of samples large enough to include 
a normal proportion of rock fragments. If these are very large 
they may be broken down to maximum dimensions of about 2 inches 
without appreciable alteration of their relations to moisture, but 
Fig. 
-Echard pans, 7 by 3 inches, containing seedlings. 
that is all that can be done. These rocks can not be eliminated 
altogether, as it is found that the more permeable of them may hold 
1 to 2 per cent of nonavailable moisture. They are distinctly a 
part of the soil and it is their presence which, in a large measure, 
makes the soil capable of supporting forest growth. 
A pan (fig. 3) which meets these requirements is made of 20- 
gauge or 24-gauge galvanized iron, 3 inches deep and 7 inches in 
diameter. Half a dozen small perforations in the flat bottom permit 
drainage while the seedlings are being started, and aeration after 
the surface of the soil has been sealed over. When filled to a depth 
of 2^ inches, such pans hold 3 to 6 pounds of soil. 
To avoid any chemical change in the soil, but more particularly 
to keep it receptive toward moisture, the dry weight of soil placed 
in the pan is determined rather by moisture samples secured as the 
pan is being filled than by drying the whole mass. The latter, more- 
over, is a slow process, especially with soils of low conductivity. 
82769—22 6 
