100 ECONOMIC WOODS OF THE UNITED STATES 



bluish. Vessels with spirals; perforations scalariform with 

 many bars; pits into ray cells half-bordered. Wood fibres 

 with spirals; pits bordered. Rays heterogeneous; of two 

 kinds: (1) Large (3-6 cells wide and up to 80 cells high) 

 with all except marginal cells uniformly low ; (2) fine (mostly 

 uniseriate and few to many cells high) with all cells large. 

 Holly, Ilex opaca Ait. (S, C). 



b 2 Pores not in radial lines although often in short 

 radial groups; frequently crowded. Wood paren- 

 chyma sometimes in tangential lines but not visible 

 with lens, except indistinctly in Cornus and occasion- 

 ally in Fagus. 



a 3 Rays quite distinct to unaided eye. (For b 3 , see 

 p. 103.) 



a 4 Conspicuously broad rays present; not aggre- 

 gated. 



a 5 Rays nearly all broad, numerous; fairly regu- 

 larly disposed and conspicuous on tangential 

 surface; of deeper color than surrounding 

 tissue, producing very distinct "silver grain " 

 on radial or "quarter-sawed" surface. Wood 

 parenchyma in irregular tangential rows 

 but not visible with lens. Pores crowded. 

 Woods fairly dense, usually cross-grained, 

 splitting irregularly; sp. gr. .47-57. Color 

 light brown, often striped. Late wood thin, 

 of lighter color than the early wood. Vessels 

 without spirals; perforations mostly simple but often 

 scalariform with few bars; bordered pits sometimes 

 scalariform; pits into ray cells half -bordered. Rays 

 homogeneous. Wood fibres with bordered pits. 

 Sycamore or Buttonball, Platanus occidentolis 

 L. (C, N, S); P. racemosa Nutt. (Ps); P. 

 wrightii Wats. (Rs). 51 

 b 5 Only a portion of rays broad ; variable, irregu- 

 larly distributed; readily visible on tan- 

 gential surface; intermediate rays very fine. 

 Color of rays not pronounced, hence "silver 

 grain " less conspicuous than in preceding 



