56 THE AMERICAN MONTHLY [March, 



greens. The other great type, the deciduous trees, is represented by 

 Fig. 8, which is a small portion of a transverse section of the poison 

 oak, a species of sumach. Here the spring growth is noticeable from 

 the numerous large openings, which are sections of open ducts, while 

 the later growth, composed mostly of small, thick-walled, dense cells, 

 makes up the bulk of the annual rings. The difference in structure is 

 shown at a glance, and it marks an equally great difference in quality. 

 The large ducts are usually filled with air, but their thick walls give 

 elasticity to the wood, while the very small, thick-walled cells, packed 

 closely together, give strength. The most valuable woods — such as 

 oak, ash, and hickory — generally have their ducts in rows, confined to 

 the spring growth, while those in which the ducts are scattered indis- 

 criminately throughout the wood — as walnut, linden, maple, cornel, 

 gum, poplar, and mulberry — are generally much less dense, elastic, and 

 durable. Marked differences occur, of course, in individual cases, owing 

 to variations of soil, moisture, or climate, as trees are influenced to a 

 large extent by their surroundings. The white oak in Michigan, with 

 dense wood, narrow circles of growth, and almost invisible rows of 

 ducts, when growing in the more genial climate and rich soil of west- 

 ern Tennessee shows -annual circles half an inch wide, with very narrow 

 bands of denser growth to mark the short, mild winter. Still further 

 south, and the rank moisture of Louisiana urges the wood into a too 

 luxuriant development, resulting in a coarse, brash, quickly-decaying 

 timber growth. So, too, a dry, upland, gravelly soil will only allow a 

 limited development, and a tree becomes dense and hard, but small, 

 and the wood generally is brittle from too great a proportion of lignified 

 tissue. 



Lastly, as a specimen of a still different kind of wood, Fig. 9 is given, 

 representing a transverse section of black walnut. The open, porous 

 character of the wood is beautifully shown in the engraving, the ducts 

 being very numerous and large, scattered indiscriminately throughout 

 the whole wood, and the bands of winter growth being reduced to almost 

 nothing. 



These few specimens of tree growth only just begin to show the va- 

 rieties which may be seen ; but they are sufficient to indicate the value 

 of the work and the accuracy with which, from such examinations, con- 

 clusions can be drawn as to the growth and character of any wood. 

 Much more can be learned from sections cut parallel with the medul- 

 lary rays, or radially, and from others cut at right angle to the medul- 

 lar}' rays, called tangcntially ; but it was not possible to represent them 

 all in the limits of one article. Enough to say, that microscopic exami- 

 nations aid very greatly in showing why and how lumber warps ; how 

 to cut it to avoid this ; why sap wood decays quickly ; how to cut to 

 get the prettiest pattern ; why rift-sawed lumber wears the best ; the 

 causes of dry rot; the relative values of diflerent kinds of timber, and 

 the thousand and one other questions that are continually coming up. 



Preservation of Urine. — As it is not always possible to examine a 

 sample when fresh. Dr. Frank L. James, of St. Louis, Mo., suggests 

 adding a crystal of Naphthalin as a preservative. This will accomplish 

 the desired resvdt without either afl'ecting the character of the urine or 

 modifying^any subsequent tests. 



