48 EXPERIMENT STATIOxX. [Jan. 



is likely to vary from day to day to some extent. This variation 

 is not only found in the different percentages of gas constituents 

 but in the other products. 



The principal features in the tissues from which diagnosis 

 may be made are odor and color, although it is possible by the 

 use of chemicals to obtain reactions and to detect certain prod- 

 ucts in the tissue of trees killed by gas. There are different 

 odors associated with the wood of trees which die from various 

 causes, and it is necessary to become familiar with these to be 

 able to differentiate them. Molds and other micro-organisms 

 acting on the sap of trees dying from various causes often cause 

 decomposition, with certain resultant odors which occur in a 

 great variety of trees. But always in trees killed by gas may be 

 found peculiar characteristic odors difficult to describe, even if 

 the tissue most seriously affected is found. This tissue is 

 usually at the base of the tree or in the larger roots near where 

 the tissue has absorbed the most poison, and it is more easily 

 recognized after a tree has been dead for a few weeks or months. 

 The odor is more prominent in moist than in dry trees. It can 

 be detected in the tissues of the bark as well as of the wood. 



Sometimes this odoriferous wood is found deeper in the sap- 

 wood than at other points, and can be recognized in the stumps 

 of trees freshly cut, but in old stumps where decay has set in it 

 is not always discernible. In such cases some part of the root 

 system, if dug up, is likely to give a characteristic odor except 

 when the wood has become too dry and a more or less advanced 

 stage of decay has set in. As previously stated, the odors are 

 difficult to describe, as they are often associated wath the prod- 

 ucts of decomposition. Moreover, the odors of one tree are en- 

 tirely different from those of another, so one has to become 

 familiar with the characteristics of each species of tree which 

 he is diagnosing. The natural odor of the maple is quite dif- 

 ferent from that of the elm, horsechestnut or red oak, and their 

 products of decomposition differ also. Nevertheless, the charac- 

 teristic odor given to the tissue by the products of illuminating 

 gas can be differentiated quite easily and accurately by any one 

 familiar wnth them. Sometimes these odors are found in a con- 

 siderable part of the tissue of the trunk, but more often they are 



