242 JOURNAL OF FORESTRY 



That bordered pits are regions of danger is well known and con- 

 sequently comparative counts of their distribution were made for two 

 sections of Taxodium. In the average tracheid shown in figure 7 

 there are about 500 bordered pits scattered over the two radial walls. 

 In the wood shown in figure 1 they averaged 50 to the mm. on one 

 side of the spring tracheids while the brash one showed on average 

 of about 70 to the mm. In the summerwoods of the two sections the 

 proportion was about IT to 40. This difference in the number of 

 bordered pits, each one a source of weakness, becomes even more 

 strikino- when it is associated with the relative proportions of late 

 growth in each, which was in the one case 38 per cent and in the other 

 2 per cent, thus producing a volumetric relative distribution of 3 to 7 

 in the strong and brash timbers respectively, and since this numerical 

 difference is also associated with the larger size of those in the spring- 

 wood, the eft'ect on strength is even greater than numbers alone would 

 indicate. 



In summing up the features characteristic for Taxodium distichuui 

 it would appear that the factors which are influential in detemiining 

 brashness are : the amount of summerwood, the thickness of the cell 

 walls, and the number and size of the bordered pits. The specific 

 gravity, being as it is but an outward manifestation of the anatomical 

 organization, can not be included among the sources of weakness ; a 

 fact, however, which in no way minimizes its value as an indicator of 

 the fitness of wood for structural purposes. 



The tulip poplar, Liriodendron tulipifera, is one of the most variable 

 as well as one of the most treacherous of woods. Some sticks are 

 heavy and strong while others are weak and brash. The broken sur- 

 faces of the two types of tulip poplar are very characteristic as can be 

 seen by a reference to figures 9 and 13 which show breaks typical of 

 weak and strong woods. Both were examined microscopically under 

 strong reflected light in order to determine their most vulnerable points. 

 In the brash one, illustrated in figure 9, the vertical elements almost 

 without exception show a transverse break while the short splinters 

 exhibit a tendency to split along the vessels or through the rays. The 

 fibers when not broken abruptly are for the most part separated through 

 the central part of the cell rather than through the middle lamella, and 

 cases where they are pulled apart at the ends are rare. In figure 9 a 

 hand lens will show the vessels and rays which have been broken so 

 smoothlv that every antomical detail is visible. In general the wood 



