i6 Forestry Quarterly. 



cavity on the right. It may be noted that the bordered pit in the 

 centre of the photomicrograph is partly filled with a resinous 

 substance and slight penetration occurs. At the extreme left is a 

 so-called "medullary" ray which, with carbon particles of this 

 size, remained unpenetrated. Fig. 6 illustrates a tangential sec- 

 tion of the "summer-wood" of an ordinary long-leaf pine paving 

 block. Since the heavy tar oils had penetrated almost exclusively 

 the dense bands of "summer-wood", it is significant, in view of 

 Weiss' theory, that the penetration from one cell to another 

 takes places by means of the bordered pits and not by cracks or 

 "slits" in the thick secondary walls. 



As a "control" for these experiments the writer tested the 

 penetration of the carbon mass with pieces of freshly cut green 

 sapwood. A deeper and easier penetration was secured in green 

 material of white pine, pitch pine, spruce, hemlock, larch, and 

 cedar than could be secured in the same material after thorough 

 kiln or air drying. In both cases the material was subjected to 

 similar temperatures (65° F.), pressures, and duration of treat- 

 ment. At first negative and positive pressures of approximately 

 one atmosphere were used. In order to obviate the possibility 

 that the membranes were ruptured by these pressures, two series 

 of tests were made. In the first, experiments were made to de- 

 termine at what pressure the pit membranes could be broken. 

 With pressures up to 25otb. per sq. in., the maximum capacity 

 of the pressure cylinder used, the membranes of all conifers re- 

 mained unruptured. This was undoubtedly due to the valve-like 

 action of the torus which has been described earlier in this 

 article (see text Figure C and Figures i and 3). A second series 

 of experiments was then made to test the penetration of the 

 carbon mass under very slight hydrostatic pressure. Hartig 

 showed that if a stick of freshly cut green sapwood several inches 

 long was held in a vertical position and a drop of water placed 

 upon the top it disappeared very quickly and appeared at the 

 lower end of the stick. The writer repeated this experiment, con- 

 necting the upper end of the stick to a rubber tube of a few cubic 

 centimeters capacity. If a sufficiently dilute solution of the 

 carbon mass was used the water passed rapidly through the stick 

 carrying the carbon particles with it. Fig. 4, a longitudinal tan- 

 gential section of freshly cut green white pine sapwood, shows the 



