30 WOOD AND FOREST. 



distinct, are to be seen scattered all thru the wood. It is by the num- 

 ber and distribution of these pores that the different oak woods are 

 distinguished, those in white oak being smaller and more numerous, 

 while in red oak they are fewer and larger. It is evident that the 

 greater their share in the volume, the lighter in weight and the 

 weaker will be the wood. In a magnified cross-section of some woods, 

 as black locust, white elm and chestnut, see Chap. Ill, beautiful pat- 

 terns are to be seen composed of these pores. It is because of the 

 size of these pores and their great number that chestnut is so weak. 



(2) The summer wood is also distinguishable by the fact that, as 

 with the conifers, its cells are smaller and its cell walls thicker than 

 those of the spring wood. The summer wood appears only as a nar- 

 row, dark line along the largest pores in each ring. 



(3) The lines of the pith rays are very plain in some woods, as in 

 oak. No. 47, Chap. III. 



(4) The irregular arrangement and 



(5) Complex structure are evident, and these are due to the fact 

 that the wood substance consists of a number of different elements 

 and not one (tracheids) as in the conifers. 



Looking at the radial section, Fig. 20 : 



(6) If the piece is oak, the great size of the medullary rays is 

 most noticeable. Fig. 32, p. 38. They are often an inch or more 

 wide ; that is, high, as they grow in the tree. In ash they are plain, 

 seen thru the microscope, but are not prominent. 



(7) The interweaving of the different fibers and the variety of 

 their forms show the structure as being very complex. 



In the tangential section,. Fig. 20 : 



(8) The pattern of the grain is seen to be marked not so milch by 

 ihe denseness of the summer wood as by the presence of the ves- 

 sels (pores). 



(9) The ends of the pith rays are also clear. 



In diffuse porous woods, the main features to be noticed are: In 

 the transverse section, Fig. 21 : 



(1) The irregularity with which the pores are scattered, 



(2) The fine line of dense cells which mark the end of the year's 

 growth, 



(3) The radiating pith rays, 



(4) The irregular arrangement and, 



( 5 ) The complex structure. 



