88 



GENERAL BOTANY 



transverse, radial, and tangential sections. Fig. 48 illustrates the 

 appearance of the annual rings and of the spring and summer 

 wood as they appear in transverse and longitudinal sections 

 of stems four and five years of age. In the transverse cuts at 

 the upper end of Fig. 48, a and >, the spring and summer wood 

 appear as in the oak (Fig. 47), but in the radial (a) and oblique 

 (5) sections they present a very different appearance. In the 

 radial section the spring and summer wood appear as narrow 





FIG. 49. Sections of wood of bird's-eye maple (Acer saccharum) 



Transverse section at the left, radial section in the center, and tangential (curly grain) 



at the right in the figure. The curly grain is due to irregularities in the growth of 



the annular rings. Photograph furnished hy the United States Forest Service 



and wide vertical lines or bands, while the wood rays run across 

 the grain as darker horizontal bands. In the oblique-tangential 

 section the rays have a similar appearance in the upper semi- 

 radial portion of the section, but in the lower tangentially cut 

 portion they show as vertical lines of varying height and width. 

 This difference in appearance in the wood rays is due to their 

 shape and their radiate arrangement in the tree trunk. The 

 " silver grain " in finished woods, notably in quarter-sawed 

 oak, is due to the wide wood rays, which have a shining, 



