ROLE OF THE MICROSCOPE 177 



With the opening up of the latter sources of supply, many new woods 

 are being offered for sale in the larger markets of the world. If it 

 were possible to trace these woods, by means of an anatomical key, 

 to the botanical species from which they are derived, considerable 

 assistance could be given to lumbermen, not only in the classifica- 

 tion of tropical woods, but ulso in providing them with important in- 

 formation in regard to probable sources of supply, etc. 



Another important field of usefulness, for a very accurate and re- 

 liable key, should be found in cases of controversy or litigation, e. g., 

 when it is necessary to determine with certainty whether an in- 

 ferior or undesirable wood has been substituted for a more valuable 

 variety. 



II. VARIABILITY OF ANATOMICAL CHARACTERS 



Most botanists and microscopists, who have constructed anato- 

 mical keys for distinguishing different woods, have assumed that 

 anatomical characters are very constant, and less liable to fluctuate 

 than are gross or macroscopic characters. If not expressly stated, this 

 assumption is implied by the fact that, although the old "rule of 

 thumb" systems of classifying woods, according to their superficial 

 characters, were based upon the study of a very large amount of ma- 

 terial, the anatomical keys, that are substituted for them, have been 

 constructed after a comparatively limited number of specimens have 

 been examined. 



In view of the fact that, owing to the methods used in their con- 

 struction, the diagnostic value of most anatomical keys is directly 

 dependent upon the accuracy of this premise, it is essential that special 

 investigations should be made to determine the limits of variability 

 of a number of anatomical characters. That is to say, selected char- 

 acters should be studies in a wide range of specimens, not only in 

 material from all parts of single trees, but also in wood from plants 

 that have grown under very different environmental conditions. 



The writer is gradually bringing together the necessary materials 

 for a number of investigations of this character. Sufficient data 

 have already been accumulated to afford some clue in regard to the 

 variability of a number of anatomical characters that have been used 

 in distinguishing commercial products. 



