16 



BULLETIN 523^ U. S. DEPARTMENT OF AGEICULTUEE. 



by the contrast of the belt of springwood containing numerous large 

 pores with that of the denser smnmerwood 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 scai-cely 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. 



Fig. 3. — Transverse sections of ash wood under small hand Icnse ; A, black asb ; B, white 

 ash; C, green ash. Taken from Bulletin 10 of the Division of Forestry (1895), by 

 Prof. Filibert Roth, 



It is difficult and often impossible to distinguish, with any degree 

 of certainty, the wood of the different species of ash. (Pis. 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 Koth : ^ 



1 rhotomlcrograpbs of slides made by A. Koeliler, of tlie Forest I'roducls Laboratory. 



