HARDWOOD RECORD 



iloss ou trees is no more universal than rough bark is. Sometimes 

 it exists, sometimes not. Where it is not found, it is, of course, 

 unavailable as a guide in shaping a course, and where it is abundant 

 it may be equally useless. In Louisiana the so-called Spanish moss 

 covers tlie trees completely. There is no difference as to the sides 

 of trees. Xorth, south, east and west all get it alike. The same 

 observation holds for the greenish-yellow moss that clothes the for- 

 ests on some of the far western mountains. The points of the com- 

 pass apparently have nothing to do with its abundance or scarcity. 



In the nortliern and eastern hardwood regions — that is, east of the 

 Mississippi river — many people refer to lichens as moss. In some 

 localities these seem to prefer the north sides of trees, but in other 

 places no preference whatever appears to be shown. A person who 

 would guide his course by this sign would as likely as not travel 

 toward every point of the compass in course of a day in the woods. 



"Large limbs pointing south" are likewise a delusion. Possibly 

 the limbs on the southern side of trees average a little larger than 

 those on the north side, but tlie differences are so slight and the 

 exceptions to the rules so many that no practical advantage can be 

 taken of the fact, if it really is a fact. Limbs and tree tops grow 

 and lean toward light and open space. If these prevail on the 

 southern side, the largest branches will likely grow there; but open 

 space on the north and thickets and shade on the southern side, 

 will induce the largest limbs to develop on the north side. Any 

 woodsman knows that if two trees grow close together with open 



space all round, they will have few limbs on the sides facing each 

 other, but long ones on the sides opposite. Points of the compass 

 have little to do with it. Local conditions control. Frequently the 

 prevailing wind has more influence than all other forces combined. 

 If the prevailing w'ind is from the south, the longest limbs will point 

 north, away from the noonday sun; if the wind is from the east, 

 the dominant branches will point west. This is one of the com- 

 monest sights on the Atlantic coast, w'hile on the Pacific coast iu 

 California where the full sweep of the sea winds strikes standing 

 trees on their western side, their largest limbs extend toward the 

 east. There is a certain mountain in California so situated in rela- 

 tion to surrounding mountains that its summit is swept almost con- 

 stantly by south wind. The trees have scarcely a limb on their 

 southern sides, but stand like Hag poles, with what few branches 

 they have whipped out towards the north like streamers. In the 

 southern Appalachian mountains the abnormally-developed one-limb 

 character of the Fraser fir attracts attention of most people who 

 travel through the high regions where it grows. These uncouth, 

 overgrown branches are liable to point in any direction — straight 

 north as often as straight south. 



It ought to be apparent, therefore, that it is time to revise some' 

 of the old-time misconceptions of nature's guideposts in the forests. 

 If there is any sure way of knowing north, south, east, or west by 

 reading signs on the trees,, some one ought to have made the dis- 

 coverv known before this time. 



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Measurement of Shrinkage 



It is a matter of eonmion observation that wood shi'iuks when it 

 dries, but not equally in all directions. Shrinkage is due to the fact 

 that while the cell walls grow thinner in drying they shorten imper- 

 ceptibly. Other things being equal, the thicker the walls of the 

 wood cells, the greater their shrinkage, but this applies only to dif- 

 ferent portions or specimens of the same species and cannot be used 

 in comparing unrelated woods. For instance Osage orange is one of 

 our hardest, heaviest and densest woods, yet its shrinkage in volume 

 from a green to an oven dry condition is less than half that of some 

 of the hickories. 



If one takes an exact cube of green wood so cut that two of the 

 faces represent cross-sections, two radial, and the other two tangential 

 surfaces, and dries it out completely, he will find that while there 

 has been little if any alteration in the length of the piece — that is, 

 ■longitudinally or parallel with the fibers — the other dimensions have 

 changed, the tangential shrinkage or in direction of the rings of 

 growth being considerably greater than that along the radius — often 

 twice as great. This is quite different from the behavior of a com- 

 paratively homogenous substance such as metal or concrete, and ex- 

 plains why shrinkage is so often followed by checking and splitting. 

 Thus if one saws a complete section off the end of a green hardwood 

 log and allows it to dry it will probably split to the center and in 

 time a large V-shaped opening will appear. Upon subsequent soak- 

 ing this cleft wm close up. If shrinkage were uniform the section 

 would merely grow smaller upon drying. 



This question of shrinkage has a very important bearing on the 

 use of wood. When squares are cut or staves made from green 

 material it is necessary to allow for shrinkage, otherwise the final 

 dimensions may be so small that the pieces wiU have to be culled. 

 If wood once shrunk would remain in that condition one of the 

 greatest ills of which wood is possessed would not exist. But the 

 cell walls absorb water readily not only in liquid form but also from 

 the air. Wood dried at high temperature "works" less than air- 

 dried material, even after it is brought back to an air-dry condition. 

 No matter to what degree of dryness wood may be brought in the 

 kiln it is important that at the time of manufacture it should contain 

 approximately the amount of moisture it wUl normally have in use. 

 The U. S. Forest Service has made a great many shrinkage 

 measurements in connection with the tests on the strength values 



of woods. The results obtained are for use as average working 

 values rather than the basis for detailed study of the principles 

 involved. A common method of making the tests is to take from 

 each ibolt two specimens one inch thick, four inches wide and one 

 inch long. They are taken close together so that the results from 

 the two wiU be comparable. One of the specimens is cut with its 

 width in the radial direction and is used for the determination of 

 radial shrinkage. The other has its width in the tangential direction 

 and is used for tangential shrinkage. The specimens are carefully 

 weighed and measured while in a green condition ; they are then air- 

 dried and afterward oven-dried at a temperature of 212 degrees F., 

 until a constant weight is obtained, when they are again weighed 

 and measured. 



To determine the shrinkage in volume the test specimens are sub- 

 merged in water both before and after drying. The exact amount 

 of water displaced by the blocks is measured, and corresponds to 

 the volumes of the material. In the following table the results of 

 the measurements on twenty hardwoods are given, the species being 

 arranged in the order of their volumetric shrinkage beginning with 

 the greatest. 



Shrinkage in Volume of Twenty Haedwoods teom Green to Oven-Dry 

 Condition 



Radial Tangential 

 Volume, shrinkage, shrinkage, 

 per cent, per cent, per cent. 



1. Big shellbark hickory (Uicoria laciiiiosa) . 1S.3 7.7 13.2 



2. Pignut hickor.v (H. glabra) 18.2 7.2 11.6 



3. Mockernut hickor.v (H. alba) 17.7 7.7 10.9 



4. Swamp white oak (Quercus platan oides) . 17.7 5.5 10.6 



5. Yellow birch {Betula lutea) 17.0 7.9 9.0 



6. Shagbark hickory (Hicoria oiata) 17.0 7.2 10.6 



7. Beech {Fagus americana) 16.5 4.6 10.5 



8. Post oaU {Quercus minor) 16.0 5.7 10.6 



9. Slippery elm {V!mus pubesceiis) 15.5 5.1 9.9 



10. Black oak (Quercus velutina) 15.1 4.7 9.5 



11. White oak (Quercus alba) 15.4 5,3 8.8 



12. Basswood (Tilia americana) 14.5 6.2 .S.4 



13. Sugar maple (Acer saccharum) 14.3 4.9 9.1 



14. Hackberry (Celtis oceidentalis) 14.0 4.2 8.9 



15. Bed oak (Quercus rubra) 13.8 4.0 8.3 



16. Sycamore (Platanus oceidentalis) 13.5 5.0 7.3 



17. White ash (Fraxinus americana) 12.6 4.3 6.4 



18. Tupelo (iVi/sso aquatica) 12.4 4.4 7.9 



19. Osage orange (Toxylon pomiferum) . . . . 8.9 — — 



20. Honey locust (Olediteia triaeanthos) .... 8.6 — — 



