288 



TEXTBOOK OF BOTANY 



in the lives of the diff dwellers and other ancient peoples as far back as a 

 diousand years or more/ 



Ring-porous, diffuse-porous, and non-porous wood. When the vessels 



iff- \\'' mSf \i\ 



> t I 



Fig. 108. Bing porous wood of white oak (A, above), diffuse porous wood of river 

 birch (B, below). Photos from Forest Products Laboratory. 



and xylem cells that develop in spring are large and numerous (Fig. 

 108A), the annual rings are particularly conspicuous. Such wood is ring- 



1 Papers by A. E. Douglass and Waldo S. Glock. Carnegie Institution of Washington, 

 D. C. Leonardo da Vinci, o\er 400 years ago, recorded tlie relation of tree-ring growth to 

 weather conditions. The matter did not receixe serious attention, howexer, until 1901 when 

 Douglass began to report his observations. 



