Preservative Treatment of Timber. ii 



Description of Plate I. 



fig. I. Radial longitudinal section of a western hard pine showing 

 spiral cracks or "slits" in the thick walls of the ''summer-wood" (Sr). 

 The thin-walled spring tracheid (Sp) at the right is seen to be unrup- 

 tured. X 400. 



Fig. 2- Cross section of the dense fibers of a broad-leaved tree or 

 "hardwood" showing drying cracks in the thick secondary walls. The 

 darker colored primary walls which enclose the inner layer are seen to 

 be unruptured. X 500. 



Fig. 3. Tangential longitudinal section of the "summer-wood" of west- 

 ern yellow pine showing spiral cracks or "slits." X 500. 



Fig. 4. Cross section of both the "summer" (Sr) and "spring-wood" 

 (Sg) of a Mexican hard pine. The cracks or slits are confined to the 

 thick secondary wall of the "summer-wood." The dark primary walls 

 are seen to be unruptured. X 500. 



Fig. 5. Longitudinal section of freshly cut white pine sapwood taken 

 from the immediate vicinity of the cambium showing the fine spiral bands 

 which occur in specialized cells that resist compression. X 700. 



Fig. 6. Longitudinal section of loblolly pine tracheids showing striated 

 effect produced by incipient stages of decay. X 1000. 



Fig. 7. Cross section of the air-dried "summer-wood" of a very dense 

 specimen of long-leaf pine. The thick secondary wall as well as the 

 primary and tertiary walls are seen to be unruptured. Compare Fig. 4. 

 The faint lines crossing the section from right to left were made by the 

 minute irregularities which occur on the edge of even the sharpest micro- 

 tome knife. X 500. 



