82 JOURNAL OF THE [july, 



The durability of White Cedar in situations where it is alter- 

 nately wet and dry or in contact with the ground, is in strong 

 contrast to many other woods of much harder and firmer texture, 

 and for this reason it is so largely used in ship building, for tel- 

 egraph poles, fence posts and railway ties. The decay of this 

 wood is so slow that when used for railway ties, the rails crush 

 the fibres under them before the ties decay in the ballast, and 

 are removed more on account of mechanical destruction than 

 decay — as a rule. 



The photomicrograph of the transverse section. Fig. 1., indi- 

 cates at once, by the nearly uniform thickness of the cell walls 

 for the entire annular layer, that it is not a strong wood, as only 

 a few rows of cells in the last of the season's growth are tabular 

 and thickened, this is in strong contrast to the number of rows 

 in a layer of Yellow Pine, Pintis palustris (Mill). 



The tracheids in White Cedar are comparatively small in diam- 

 eter, only ranging from 0.0013 to 0.0015 o^ ^'^ inch, while the 

 lumen is from o.ooii to 0.0013 o^ ^'^ inch, showing that the 

 walls are very thin, which fact to a great extent accounts for the 

 low specific gravity and softness of the wood. 



Another feature to be noticed in Fig. I. is the comparatively 

 small number of bands of medullary rays, showing as dark lines, 

 crossing the (Fig.) page. The bands are only of single width 

 of cells, and the latter so small that the lumen does not show in 

 a magnification of 50 diameters. In a tangential section the 

 bands are seen to be composed of only 2, 3, 4, 6 or 8 superim- 

 posed cells, the first three predominating. In a square inch of 

 wood only about 400 of these bands occur, a comparatively 

 small number, and these do not furnish much resistance to in- 

 dentation, but are very effectual in checking the tendency of 

 decay, from spreading laterally. 



Another feature shown by the transverse section is the absence 

 of resin ducts, common to many of the other coniferous woods. 

 Much of the resin is confined to special resin cells, the ends of 

 which appear as dark cells in the photomicrograph. This fea- 

 ture is common to the most durable of the coniferous woods. 

 The medullary rays of the duramen especially, also contain 

 deposits of resinous matter, which in most cases remains intact 

 after the surrounding tissue is well advanced in decay. 



