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inently visible. These woods are mostly the hard woods of the broad-leaf 

 trees, their compact summer-wood being the hard part. The diffuse-por- 

 ous woods, which have their vessels and pores of smaller size but larger 

 number, more or less evenly distributed, are mostly the soft wood like pop- 

 lar, aspen, tulip tree; the summer-wood being also porous, and only the last 

 one or few layers of cells being made up of thick-walled, small-lumened,, 

 compressed cells, making distinction of the annual ring difficult. The con- 

 'ifers represent the non-porous woods, that is to say, they have no pro- 

 nounced large-lumened vessels or "pores." Their structure from begin- 

 ning to end is the most simple and uniform. The only difference between 

 summer- wood and spring- wood is that the former has the cells (or tra- 

 cheids, so-called ) thicker-walled and compressed in radial direction. Here, 

 too, we will find soft and hard woods. The hard woods being represented 

 by the Yellow pines and the Douglas fir, which form many summer-wood 

 cells the harder, dark-colored part of the annual ring while others, like 

 the White pines, cedars, etc., have only a few such compressed summer- 

 wood cells, the annual ring being less pronounced. 



The varying distribution of large and small pores in the broad-leaf 

 trees permit not only further distinction of genera and species, but also 

 judgment of qualities. It stands to reason that a larger percentage of the 

 thick-walled elements, ceteris paribns, means heavier, stronger wood, so 

 that by mere physical inspection at least a comparative judgment of the 

 value of wood may be formed. 



Since according to species the proportion of summer-wood and spring- 

 wood varies with the rapidity of growth (width of ring) and since the for- 

 ester can make trees grow faster or slower, he has it partially in his hand 

 to produce difference in quality. 



Another feature of the structure which are both used for purposes of 

 identification and exercise an influence on technical qualities, are the so- 

 called medullary or pith rays. While most cell tissues and wood fibres lie 

 with their longest diameter in the direction of the length or axis of the tree 

 or branch, the pith rays, aggregates of cells, lie with their greater diameter 

 in radial direction interrupting the straight course of the wood fibre. They 

 are, therefore, points of weakness. On the cross section they appear as 

 radial lines, finer or broader, sometimes so fine, as in the conifers, as to be 

 hardly distinguishible, again so broad, as in the sycamore and the oak, as to 

 form a most prominent feature of the structure. It is especially in the rad- 

 ial and tangential cuts, which are the ones mostly exhibited in structures, 

 that the pith rays play a role, appearing as different colored plates in the 

 quarter-sawed maple, beech or oak, and as narrow indentations on the tan- 

 gential cut. The absence or rather scanty development of pith rays in con- 

 ifers is one of the reasons of the uniform quality and behavior in shrinking 

 of these woods, while the difficulty in seasoning oak without checks is 

 largely due to the presence of many highly developed pith rays. 



