A LABORATORY EVALUATION OF WOOD PRESERVATIVES 197 



fungus, but suggested that at least two species should be used in each 

 test. After three or four months' exposure to the wood-destroying 

 fungi, the blocks are removed from the flasks, freed from adhering 

 mycelium, and the weights taken before and after the test period used 

 as a measure of the amount of decay. 



The kolle flask method has much to recommend it, overcoming as 

 it does many of the difficulties inherent in the petri dish technique. 

 However, the test as standardized at Berlin presents serious drawbacks. 

 The kolle flasks are expensive, comparatively fragile, difficult to 



in 



Fig. 2 — Assay by kolle flask method. Porta incrassata used in comparison of southern 

 pine heartwood versus sapwood. 



handle, inconvenient to store, and maintenance of proper moisture 

 conditions is particularly difficult. For really satisfactory results the 

 flasks during the tests should be kept at a constant humidity and 

 temperature. Despite all precautions there is the ever-present danger 

 of excess moisture and resultant lack of decay should the test block 

 touch the agar or any condensed moisture on the flasks. Another 

 unusual problem arose when certain over-ambitious fungi rotted the 

 cotton plugs used to stopper the flasks and even continued to grow 

 into other flasks where they did not belong. 



