164 Relation of Annual Rings to Age. 



Warring* remarks that: "Trees in the tropics do form rings 

 regularly, even when the conditions of growth are absolutely uni- 

 form, e.g., mangroves growing on muddy margins of tropical 

 rivers." He also endeavors to strengthen this view by citing 

 the development of rings in the orange and lemon when grown in 

 greenhouses, where the conditions are supposed to be subject to 

 but slight variation all the year round. £achs f remarks that " In 

 tropical, woody plants, when several years old, the additions 

 to the wood formed in each successive year are not generally 

 distinguishable on a transverse or longitudinal section ; the entire 

 mass of the wood is homogeneous." And he very properly makes 

 a distinction between such growth in warm climates and that 

 where the alteration of seasons, and so of growth, is sharply 

 defined. Dr. A. S. Baldwin J cites the case of a tree on his own 

 ground in Florida, which was less than thirty years old when 

 cut, but which exhibited very nearly forty rings of growth, and he 

 infers from this and similar cases that the rings are determined 

 by meteorological conditions, and represent periods of physiolo- 

 gical rest and activity, which may be repeated whenever the 

 external conditions are favorable. 



STRUCTURAL CONSIDERATIONS. 



An examination into the immediate cau; c of the distinction 

 between contiguous rings of growth shows it to be of a two-fold 

 nature and due (a) to localized deposition of coloring matter ; (b) 

 to structural peculiarities. In the cases of those trees which develop 

 a large amount of resinous matter or of well-defined pigment 

 this is often deposited in such a manner as greatly to facilitate 

 distinct definition of the rings. In certain cases the color may 

 be uniformly distributed throughout the entire structure; in 

 other instances, as Plnus and to a certain extent lignuin-vitse, 

 the deposition of the coloring matter is more strictly localized, and 

 generally in that part of the structure formed at the close of the 

 season's growth. The particular depth of color may arise from 

 an actual deposition of pigment associated with resinous matter, 

 as in Pinus, or from structural peculiarities which tend to in" 



* Amer. Jour, of Science, 1877, p. 395. Acad. Nat. Science, 1878. 

 t Text Book of Botany, p. 132. 

 ■ J Pop. Science Monthly, Vol. XXIV. p. 554. 



