248 JOURNAL OT* FORESTRY 



The only new feature appearing in ring-porous woods which differs 

 from those already described for the other types, is the ring-porous 

 character of the annual increment of growth. In general, the width 

 of this area of large cells differentiated for conduction appears to be 

 quite constant and independent of the width of the ring. In slow- 

 growing woods the volume of fibers and small summer vessels is nor- 

 mally small, and such timbers tend to be weak, while in rapid-growing 

 trees the strengthening tissue is much increased in amount and natur- 

 ally enough such woods are strong. 



There are certain fundamental objections to the conception that short 

 fibers are necessarily associated with brashness, since the tendency for 

 the fibers to become shorter in the hardwoods than they are in the 

 conifers is in reverse ratio to the tendency for the increase in strength 

 as between .the two types of wood. The radial rows of cells do not 

 end in one plane, but are uniformly distributed so that there would 

 be no localized line of weakness due to an inclination to offer a lower 

 resistance to pressure where the $bers are joined. And finally, obser- 

 vations of broken brash and strong weeds show that the fibers, do not 

 to any large extent puU apart at the ends, but break, split longitud- 

 inally, or separate along the middle lamella subsequent to failure in 

 the vessels and rays. 



To be sure, there are other causes for brittleness in w^ood, such as 

 incipient decay, improper drying, and the .like, which have not been 

 included in the discussion since they represent defects which are 

 acquired, rather than inherent, and consequently should not be enumer- 

 ated among the fundamental anatomical variations responsible for 

 brashness. 



CONCLUSIONS 



1. Brashness is increased by a decrease in the amount of summer- 

 wood, by a decrease in the thickness of the tracheid or fiber wall, by 

 a decrease in the volume of the fibers, by an increase in the volume of 

 the wood rays and storage parenchyma, and by an increase in the 

 number and size of the bordered pits. 



2. In the conifers the proportion of thick-walled summer tracheids 

 and thin-walled spring tracheids determines strength or weakness ex- 

 cept as this may be influenced by the rays, resin canals, and storage 

 parenchyma. In the diffuse-porous woods the percentage of fibers, 

 the thickness of their walls, and the volume of the rays and vessels 



