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 
N 
‘ | 
A 
5 
5 a ZA 
Fic. 232.—Wedge of a four-year-old pine stem cut in winter, showing, 
somewhat diagrammatically, a transverse surface (qg), a radical sur- 
face (1) and a tangential surface (t): f, f, f, spring wood; s, summer 
wood; m, pith; p, first-formed wood; 1, 2, 3, 4, the four successive 
annual rings of the wood; 7, 7, 7, junction of spring and summer wood 
in successive years; ms, ms’, ms’’’, pith-rays extending through the 
wood; ms’’, pith-rays extending into the inner bark (5); h, resin-ducts; 
br, outer bark, $. (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 
