16 BULLETIN 523, U. S. DEPARTMENT OF AGRICULTURE. 
by the contrast of the belt of springwood containing numerous large 
pores with that of the denser summerwood containing minute pores. 
The summerwood pores are arranged singly or in broken lines, the 
course of which is never radial. The pith or medullary rays are. 
very minute and scarcely distinct when viewed in cross section, which 
is an important distinguishing characteristic of the genus, but one 
which is also characteristic of osage orange and catalpa, the woods 
that most closely resemble ash in structure. Osage-orange wood can 
be distinguished readily by its bright yellow color and by its very 
great hardness and weight. Catalpa wood, on the other hand, is 
light and soft and has the pores of its summerwood arranged in 
clusters, which is not the case in ash or osage orange. 
Fic. 3.—Transverse sections of ash wood under small hand lense; A, black ash; B, white 
ash; (C, green ash. Taken from Bulletin 10 of the Division of Forestry (1895), by 
Prof. Filibert Roth. 
tt is difficult and often impossible to distinguish, with any degree_ 
of certainty, the wood of the different species of ash. (Pls. V and 
VI.) Determination of species on the basis of wood characteristics, 
therefore, is very unsatisfactory. The following points of difference 
(fig. 3) in the important commercial series, as they appear under 
the magnifying glass, are taken from Forest Service Bulletin 10, 
“Timber,” by Filibert Roth:1 
1 Photomicrographs of slides made by A. Koehler, of the Forest Products Laboratory. 
