WOOD IN GENERAL 



253 



in the wood what are known as annual rings or layers. In 

 warm regions where comparatively uniform, conditions pre- 

 vail throughout the year, many trees grow continuously and 

 the wood shows no annual layers at all. Sometimes pe- 

 culiar conditions affecting growth give rise to layers inter- 

 mediate between the annual ones, and these subdivisions of 



/ ffi 



l9 } 1 



Fig. 232. — -Wedge of a four-year-old pine stem cut in winter, showing, 

 somewhat diagrammatically, a transverse surface (<?), a radical sur- 

 face (X) and a tangential surface (0 ; /, /, /, spring wood ; s, summer 

 wood; m, pith; p, first-formed wood; 1, 2, 3, 4< the four successive 

 annual rings of the wood; i, i, i, junction of spring and summer wood 

 in successive years; ms, ms' , 7ns'", pith-rays extending through the 

 wood; ms" , pith-rays extending into the inner bark (6); h, resin-ducts; 

 hr, outer bark, f. (Strasburger.) 



the annual layers may pass entirely around the circumference 

 or they may be only partial. They are deceptive, but to 

 the practiced eye their true nature is usually apparent and 

 wherever well-pronounced layers are present it is generally 

 safe to regard such rings as marking a year of growth. 



In the woody plants which form annual rings there is also 

 formed each year in the new shoots a ring of strands each 

 consisting of an inner wood-part and an outer bark-part with 



