WOOD SOIL CONTACT CULTURE TECHNIQUE 



119 



Selection of Wood: 



For both laboratory and field assays care is exercised in selectin^f tlie 

 wood. Boards of southern pine sapwood of the shortleaf type, wliich 

 includes Pimis echinata, and Pinus taeda, are obtained from local lumber 

 dealers and are cut into sticks f x f x 32 inches. Since the square sticks 

 facilitate calculation of volume and retention of toxics or preservatives, 

 they have superseded the round saplings cited by Waterman and Williams," 

 1934. The sticks are selected on the basis of uniformity of growth, density 

 and ratio of springwood to summerwood. The jiresence of any heartwood, 



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APR-JUNE APR-AUG APR-OCT APR-DEC APR-FEB APR-APR 

 EXPOSURE PERIOD 



Fig. 5— Field test of untreated sapwood squares exjwsed at Gulfport, Mississippi, 1941-42 



sap stain or other indication of incipient invasion by fungi is cause for re- 

 jection. After classification into piles according to arbitrarily chosen 

 weight increments, twenty to twenty-five 32" sticks, for each concentration 

 of preservative used in field studies are selected by taking the appropriate 

 number of specimens from each pile to give a representative distribution 

 based on density. Since the specimens are subsequently cut in liall each 

 individual treatment is represented by 40-50 specimens. Sticks in the 

 median range of density are generally used for laboratory studies after 

 they have been cut into \" cubes (8 cc. volume). 



An experiment with untreated sticks was carried out at Gulfport, Missis- 

 sippi, where the climatic conditions are ver>' favorable for decay and also 



