86 JOURNAL OF THE [April, 



trachei'des, chiefly quadrangular. The maximum size of the 

 thin-walled cells ranges from seventy-three by sixty-six micro- 

 millimetres, to ninety by eighty-three ; and the thickness of the 

 walls ranges from two and one-half to three and one-half micro- 

 millimetres. The maximum dimensions of the thick-walled cells 

 are from fifty-three by forty micromillimetres, to fifty-six by 

 forty-three, and the thickness of the wall ranges from six to 

 eight micromillimetres. There is, moreover, a regular increase 

 in the thickness of the walls, from the interior to within four or 

 five rows of the exterior part of the ring. The thick-walled 

 tracheides form but a small portion of the ring, the resin canals 

 are not numerous, and the wood is soft, light, clear, easily worked, 

 and is desirable for pattern making. 



In the second block, — marked B, — the annular rings number 

 seven or eight per inch, and each ring contains from sixty-five 

 to seventy rows of hexagonal tracheides of about the same- size 

 with those of block A. But the thick-walled tracheides form a 

 larger portion of the ring than in block A ; the resin canals are 

 more numerous ; and the wood is harder, heavier, streaked, and 

 more difficult to work. 



I have another block, — marked C, — which is a specimen of the 

 merchantable lumber grown in the vicinity of New York. Its 

 wood differs from that of blocks A and B in having a sharp line of 

 demarcation between the thin-walled and the thick-walled tra- 

 cheides, the latter being nearly solid, — resembling Finns australis, 

 — the wood very hard, heavy, knotty, difficult to work, and liable 

 to warp badly. The rings of Bifiiis australis have about equal 

 shares of the two classes of tracheides, and the difference in 

 strength between the two classes is great. 



I brought another piece of wood, sculptured into a model rep- 

 resenting, on a scale of five hundred diameters, the general con- 

 struction of a thin-walled tracheide. The outer lamella between 

 adjacent cells is supposed to be removed. In transverse section 

 these cells appear as quadrangular, pentagonal, or hexagonal : 

 my model shows the hexagonal form. One side is carved so as 

 to represent the general appearance of a tracheide in a radial 

 section. The rounded places, which show the domes in the cell- 

 wall and their canals connecting with the lumen, are more nu- 

 merous at the ends than at the central portion of the tracheide. 

 The construction of the bordered pits which these domes form 



