Preservative Treatment of Wood. 15 



nating radial bands of thinner and thicker wall substance. They 

 concluded, however, that the membrane was unperforated). In 

 addition, numerous experiments in injecting freshly cut green 

 wood with water containing powdered solids and heavy liquids, 

 e. g. Sachs' cinnabar and mercury experiments, have led to the 

 same conclusion, that the pit membranes are entire in the wood 

 of a living tree. 



This fact afforded, apparently, a satisfactory explanation of 

 the difficulty in forcing air through green wood ; the use of salt 

 solutions, but not creosote, in the Boucherie and Kyanizing pro- 

 cesses ; the necessity for preliminary steaming or seasoning in 

 the Bethell process, etc., etc. 



The question may well be raised at this point, since Tiemann's 

 "slit"' hypothesis cannot be accepted as conclusive, what struc- 

 tural change, if any, produces the difference in the behavior of 

 green and seasoned wood. It occurred to the writer that the 

 delicate pit membranes were ruptured by the shrinkage of the 

 cell walls in drying. To determine conclusively by microscopic 

 examination whether the pit membranes are ruptured in a given 

 piece of seasoned timber is difficult, since it is not easy to elim- 

 inate the possibility that the ruptured condition was produced 

 by the process of sectioning. However, by embedding material in 

 nitro-cellulose and subsequently cutting sections with a very 

 sharp microtome knife the writer was able, in large measure to 

 overcome this difficulty, and to determine that in many pieces of 

 seasoned wood the pit membranes had been ruptured by the 

 shrinkage of the cell in drying. In order to test this point ex- 

 perimentally the writer injected the thoroughly air-dried wood of 

 several conifers with an aqueous mass containing very finely di- 

 vided particles of carbon held in suspension. Obviously this 

 dark colored liquid could penetrate only when actual openings 

 existed in the cell walls. Subsequent examination of the ma- 

 terial revealed the interesting fact that the penetration from one 

 cell to another occurred entirely through the bordered pits. Fig. 5, 

 a longitudinal section of air-dry Sequoia heartwood, illustrates' 

 the penetration of the carbon particles from one cell to another. 

 The tracheid in the centre of the photomicrograph is entirely 

 filled with the dark colored mass. The carbon particles are 

 passing through the chain of bordered pits into the adjacent cell 



