MORPHOLOGY OF WOOD 249 



bear a like relation to resistance. In the ring-porous woods there is 

 added a new feature, the width of the specialized summer area. This 

 area (the spring increment being constant) increases the tendency to 

 brashness as it decreases in amount. 



3. Failure in wood either due to flexure or compression is directed 

 by the vessels and rays. The fibers, the last to give way, break hori- 

 zontally, split in the thin-walled cells, or separate along the middle 

 lamella in the thick-walled type. Separation at the ends is uncommon. 



4. Variations in the specific gravity is quite closely proportional to 

 variations in the volume, of the fibers and the thickness of the lignified 

 walls, and less frequently inversely proportional to the volume of the 

 vessels and rays. Fiber length varies independently of variations in 

 specific gravity, and cell size is more or less constant without regard 

 to weight. 



5. The length of the fibers is not important in determining brashness. 



DESCRIPTION OF FIGURES 



1. Ta.vodiuin disticliuiii (L) Rich. A transverse section of a strong wood 

 showing broad thick-walled summer area. X 150. 



2. Same : A transverse section of a brash wood showing narrow thin-walled 

 summer area. X 150. 



.3. Liriodcndron lulipifcra L. A transverse section of a strong wood showing 

 thick-walled fibers and small, well-separated vessels. X 150. 



4. Same : A transverse section of a brash wood showing thin-walled fibers and 

 large contiguous vessels. X 150. 



5. Fra.viints aiucrkaua L. A transverse section of a strong wood showing 

 thick-walled summer fibers and two types of vessels. X 150. 



(3. Same: A transverse section of a brash wood showing thin-walled summer 

 fibers and two types of vessels. X 150. 



7. Comparative fiber dimensions of Taxodhim dlstichum, Liriodcndron tuUpi- 

 fcra, and Fraxinus ainericana. 



8. Fraxinus aiiicricaiw L. A transverse section of a slow-growing wood show- 

 ing a complete annual ring with a narrow band of summer tissue. X 50. 



9. Lirifldendron tnlipcfcra L. The broken ends of a brash wood, details of 

 which may be seen with a hand lens. X 1. 



10. Fraxinus americana L. A tangential section of a strong wood showing 

 narrow diffuse biseriate rays. X 100. 



11. Same : A tangential section of a brash wood showing difi^use multiseriate 

 rays. X 100. 



12. Ziriodendron tidipifera L. A photograph showing the broken splintered 

 end of a strong wood. X 1. 



