6 Forestry Quarterly. 



colate through this membrane gradually as through a filter, but 

 this action must be comparatively slow even under high pres- 

 sure. * -" * Whenever wood seasons (beyond its fiber satur- 

 ation point) whether naturally or by artificial means, narrozv mi- 

 croscopical slits occur in the zvalls of the fibers and tracheids 

 which render them penetrable to gases and liquids. These slits 

 do not reunite when the wood is resoaked, although they may 

 close up somewhat. The greater the degree of dryness, the more 

 penetrable the wood becomes. * * * Steaming opens up these slits 

 in the cell walls, but they are not as numerous nor as wide as in 

 air-dried material." 



This hypothesis strengthens the position of those impregnation 

 experts who claim that timber must be thoroughly air-dried to 

 secure a rapid, thorough penetration. Furthermore, it apparently 

 explains the value of preliminary steaming under pressure in 

 kiln-drying green lumber. It indicates the reason why wood dried 

 and then resoaked is weaker than the original green material, why 

 the failure of resoaked beams resembles that of dry beams, etc., 

 etc. 



A. Distribution of "Slits" in Air-dry Wood. 



As a special test of this point the writer has examined thin 

 sections cut from one hundred specimens of thoroughly air- 

 dried wood. The material included all the important timber pro- 

 ducing conifers or "softwoods" of the United States. Spiral 

 cracks in the cell walls occurred (as a result of drying or seas- 

 oning) in lo per cent, of the material examined. In the remain- 

 ing 90 per cent, the walls were entire, unruptured by the heavy 

 stresses produced by contraction of the cells in drying. The ex- 

 amination of a large number of thoroughly air-dried Dicotyledons 

 or "hardwoods" showed as in the case of the "softwoods" that 

 cracking of the cell walls in drying is of comparatively limited 

 occurrence. 



Furthermore, numerous experiments showed that air may be 

 passed as easily through the unruptured dry material as through 

 the material whose cell walls had been "slit" in drying. 



B. Distribution of "Slits" in the Annual Ring. 



In all the material of coniferous woods examined by the writer 

 the drying cracks or "slits" were invariably confined to the heavy 



