| OCR Text |
Show What Wood Is Made Of Wood Is not a so.id substance, like Iron or stone, hut is composed of sma"l hollow cells similar to an empty emp-ty honeycomb. Tho cells aro so tmall they can not be seen with out magnification, excepting in such woods as oaks, ash and cm, which have large pores or open grain. If sections of wood as thin as ono thousandth of an inch arc placed under the mlscroscope, tho character of oven tho smallest co'ls, Including Includ-ing tho peculiar markings on tho cell walls, cm be distinctly seen. At tho Forest Products Laboratory Madison, Wis., whcro tho structure of wood Is carefully studied for identification iden-tification purposes and to determine tho relation of tho structuio of wood lo Its behavior under various condl tlons, many photographs of wood sno tlons taken thrugh a mlcroscopo arc mi exhibition. Tho cells produced In tho spring or tho year aro usually largor than thoso produced in tho summer, so as to afford af-ford nn easier passage for tho Bap, which Is moro In demand In the spring than later In tho year. This dtfforonco in tho size of tho cells makes a sharp contrast between tho summer wood of ono year and tho spring wood of tho no.t, producing dlbtlnct, annual rings. By counting these rings the ago of a truo can bo determined. In tho tropics, whero the trees grow all tho year around, ordinarily no distinct annual rings aro formed, and consequently It Is Impotsiblo to detcrralno tho exnet ago of a mahogany mahog-any log. Supwood and henrtwood aro two terms used to doslgnato tho outer, 'Ighter colored wood of a tree and the Inner a darker colored wood respectively. re-spectively. All young wood Is light colored, but as It becomes older it Is infiltrated with various substances substanc-es which dUcolor It. Tho dark vrood of obony, black walnut and redwood aro striking examples of colored heat wood. Tho sapwood of all thoso trees Is light colored. Tho heart-wood heart-wood is inactive except as It furnishes furnish-es strength to a troo trunk, but the sapwood conducts tho water from tho roota to tho leaves of a tree, if n tree is glrd'ed so that all of the sapwood Is cut through, water enn no longer ascend In a treo and If will die. |
