THE PRESERVATIVE TREATMENT OF WOOD. 



II. THE STRUCTURE OF THE PIT MEMBRANES IN THE 

 TRACHEIDS OF CONIFERS AND THEIR RELATION TO 

 THE PENETRATION OF GASES, LIQUIDS, AND FINELY 

 DIVIDED SOLIDS INTO GREEN AND SEASONED WOOD.* 



By Irving W. Bailky. 



The xylem or woody portion of arborescent plants has three 

 important functions. It conducts large quantities of water, with 

 gases and salts in solution, from the roots to the cambium and 

 leaves, provides a strong and rigid stem which lifts the foliage 

 to a position when it can secure desired amounts of air and light, 

 and serves as an important reservoir for the storage of elabor- 

 ated food substances. The structure of wood has been evolved 

 to fulfill these functions and varies greatly in different species and 

 even in the same individual with variations in the expression of 

 these functions. In the less complex woods the same elements 

 serve in more than one capacity, but in those which are more 

 highly organized a division of labor takes place and certain ele- 

 ments act principally as conductors of water, whereas others 

 have almost, if not entirely, ceased to act in that capacity. It is 

 quite clear, therefore, in studying the water conducting passages 

 of wood, as a means of securing information in regard to the 

 behavior of preservative fluids when injected into timber, that 

 one must consider, to some extent at least, other functions which 

 this tissue is called upon to perform. 



If we turn to the microscopic examination of the wood of 

 coniferous trees or "softwoods," which is less complex than that 

 of the higher seed plants or "hardwoods," we find that the woody 

 tissue is composed largely of minute vertically arranged ele- 

 ments or tracheids which are devoid of living contents. These 

 cells, resembling minute tubes with closed tapering ends, are a 

 fraction of a centimeter long and serve the double purpose of con- 

 ducting fluids and providing strength and rigidity to the stem. 

 In accomplishing the latter object the cells are provided with a 



♦Contributions from the Laboratory of Wood Technology of the Har- 

 vard School of Forestry. No. 2- 



