I 



CATALOGUE OF THE TIMBERS OF THE WORLD 77 



pores. These are fairly evenly distributed, but are rather obscure and 

 mostly plugged. The medullary rays are fine and very indistinct. 



Elm, American and Canadian. Ulmns americana, Linn. U. racemosa, 

 Thomas. U. pubescens, Walt. U. crassifolia, Nuttall. U. alata, 

 Mich., and U. serotina. Weight, 44 lbs. i oz. United States, Canada. 



As with all American and some Canadian timbers, the English timber 

 merchant is confronted always with the difficulty of obtaining reliable 

 supplies, on account of the fact that these always consist of the produce 

 of several botanical species mixed indiscriminately. These suppUes may 

 vary from the fine, hard, white rock elm (obtainable from Canada twenty- 

 five years ago in large quantities of good size) through less white and 

 less hard transitional types to the soft swamp elm which is possibly 

 derived from U. alata and is Httle wanted in England. Gibson quotes 

 the respective weights of dry wood as " 40-54 lbs., 45-26 lbs., 43-35 lbs., 

 45-15 lbs., 46-69 lbs.," in the order named above, omitting U. serotina ; 

 but, according to him, U. americana is called rock elm if it grows on 

 " stony uplands," and swamp elm if on low ground. It is, therefore, not 

 difficult to account for the extraordinary differences found in both colour 

 and density between the different suppUes. Gibson states that it would 

 be difficult, if not impossible, to identify the ehns or any one of them by 

 the colour of the wood alone. Until a few years ago American and 

 Canadian elm was imported from Quebec in hewn square logs from 20 

 to 40 feet in length and 11 to 16 inches square and sometimes even larger, 

 and a very smaU import still continues, but the cost is very high, while 

 the quahty deteriorates steadily. Most of that which is now imported 

 comes from America in similar sized logs, in the round with the bark on. 



The wood is whitish-brown in colour, hard, tough, and flexible, with 

 a fine, smooth, close, silky grain ; and as it has only a small quantity 

 of sap-wood it can be worked up closely and economically. It is necessary, 

 however, to remove the sap in the conversion of the log as, unlike that 

 of the EngHsh elm, it is of a perishable character. If exposed to a current 

 of dry air it is very liable to spHt with fine, deep shakes from the surface. 

 Having this serious Habihty to rend in seasoning, the logs should never 

 be left a week exposed to the influence of drying winds without some 

 kind of protection. To preserve this timber, therefore, for future use, 

 it should be treated in the same manner as the English common elm, 

 namely by immersing it in water. ^ 



^ It has also been used in aircraft manufacture. During the war the specifica- 

 tions drawn up by the Engineering Standards Committee for the supply of rock 

 elm for aircraft limited this to the produce of Ulmiis racemosa, but in practice it 

 is doubtful if it would ever be possible to obtain supplies solely of one botanical 

 species. ^^.^,,, 



