204 Bulletin 194 



ff. Radial rows of small pores (cross) chiefly in one row, 

 becoming narrower toward the periphery of the growth 

 rings ; walls of summer-wood pores thick, 



Quercus muhlenbergii. 

 dd. Pores (cross) gradually diminishing in size from spring 

 wood to summer wood; tyloses (longitudinar) usually scarce 

 or wanting. 



e. Wood-parenchyma cells (cross) arranged in concentric 

 lines around the pores; heartwood red-brown, 



Quercus velutinao 

 ee. Wood-parenchyma cells (cross) grouped irregularly 

 around the pores; heartwood light red, 



Quercus rubra, p. 230. 

 cc. Pores (cross) all fine, indistinguishable by the naked eye at 

 three feet distance ; on close inspection, rays of one kind, all 

 fine. 



d. Pores (cross) of summer wood small and inconspicuous, or 

 when visible single, grouped, or forming short, broken lines, 

 but never forming extended radial or tangential lines. 

 e. Rays (cross) clearly distinct to the naked eye at 6-12 

 inches distance ; growth rings for the most part wide to 

 very wide; rays (radial) very high and prominent. 

 /. Pore's (cross) of late summer wood in large groups 

 of 6-many, joined tangentially by zvood parenchyma, 

 often forming tangential lines plainly visible to the 

 naked eye at a distance of 6-12 inches; tyloses (tan- 

 gential) very abundant, densely plugging the vessels; 

 wood yielding a brown stain when rubbed with a wet, 



white handkerchief Robinia pseudo-acacia. 



ff. Pores (cross) of late summer wood in small groups of 

 3-6, not joined tangentially by wood parenchyma, never 

 forming tangential lines which are plainly visible to the 

 naked eye at a distance of 6-12 inches; tyloses (tan- 

 gential) only fairly abundant, never plugging the ves- 

 sels; wood not yielding a brown stain when rubbed 



with a wet, white handkerchief Morus rubra. 



ee. Rays (cross) not clearly distinct to the naked eye at 6-12 

 inches distance, inconspicuous to microscopic ; growth 

 rings (cross) for the most part narrow; rays (radial) not 

 high and prominent. 



