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 

 the}' may be broken down to maximum dimensions of about 2 inches 

 without appreciable alteration of their relations to moisture, but 



Fig. 3. — 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 J inches, such pans hold .'5 to 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 .'is (he 

 pan i- being filled than by drying the. whole mass. The Latter, more- 



er, i- ;i -low proce . especially with soils of low conductivity. 

 -u7<;:i 'si 6 



