BROWN ON IDENTIFYING SPECIES OF WOOD. lU 



groups of small ducts will form a band parallel to and near the large 

 ducts, or sometimes a similar baud will also form parallel to the cambium 

 at the close of the season. Rarely in very rapid growth the zigzaging-may 

 disappear entirely and the bands of small ducts become approximately 

 parallel to the wood formed at the close of the season. 



For purposes of separating them into species they -may again be divided 

 with reference to the large pitted ducts. 



First, Those having at the beginning of a normal season's growth a 

 broad band of from two to four very large ducts frequently deflecting 

 the larger medullary rays. 



Second, Those having one row of large ducts with occasionally a vessel 

 in the second. Large rays not noticeably deflected. 



The hackberry and mulberry fall in the first division with the red elm 

 and may be differentiated by color of the wood, the difference in the 

 grouping of the small ducts and the gradual or abrupt diminishing of 

 the large ones. 



The American and rock elm are included in the last or second division 

 and may be separated by the difference in the size of the large ducts and 

 the thickness of the cell wall of the wood fibers. 



The maples belong to the second group of the broad leaved trees having 

 the large pitted ducts evenly scattered throughout the season. The wood 

 is medium to light in weight, even grained with sap wood of a pale cream 

 color usually tinged with rose, heart wood brown with the transverse 

 section often indistinctly radially streaked. The wood is usually straight 

 grained, easy to split, the split surfaces having a characteristic velvety 

 or satiny appearance. The radial sections often show a peculiar charac- 

 teristic mottled appearance especially in and near the heart wood. The 

 annual rings are marked by dark thick-walled cells at the close of the 

 season. The species are very similar but may be usually separated by 

 differences in weight, medullary rays and the smaller pitted ducts. 



For convenience they may be divided into two divisions based upon the 

 thickness and abundance of the medullary rays. 



The first, having numerous large rays from four — ^(occasionally only 

 three in red maple) to nine cells in thickness in the thickest part and 

 numerous small intervening ones. 



The second, those having the largest rays only one to three cells in 

 thickness — usually two — and few or none of the smaller intervening rays. 



The first includes the sugar maple and the red maple. They are very 

 similar but may be separated by the thickness of the medullary rays, 

 the sugar maple having rays from five to nine cells in thickness, the red 

 maple from four to five or occasionally three and fewer of the small 

 intermediate rays. The second includes the silver maple, box elder and 

 the mountain maple. The mountain maple is a small tree, slow growing 

 and usually has the walls of the smaller pitted ducts in the latter part 

 of the season's growth more or less distorted as viewed in transverse 

 section. The box elder can be distinguished from the silver maple by 

 its rapid growth, larger, coarser fibers and the frequent unsymmetrical 

 outline of the rays as seen in the tangential section. 



The oaks are quite distinct as a genus but the species are very similar 

 as well as extremely variable and to separate the fifty or more species 

 given by Sargent by the wood alone would be a well nigh hopeless task. 

 Nevertheless there are many well marked differences but because of insuffi- 



