wood anatomy exam II (other exam information)

wood is hygroscopic

intakes any water in its surroundings

moisture content (MC)

the ratio of the weight of water in the wood to its oven-dry weight, expressed as a percentage

MC equation

(W1 - W0 / W0) x 100

W0 = oven-dry wight

W1 = starting weight

free water

liquid water in the cell of the lumen; easy to remove, won't return unless exposed to liquid water

bound water

water molecules bound in the cell wall through hydrogen bonds; most difficult to remove

after free water is gone

there will still be water vapor in lumen

saturated

as long as there is free water in the lumen, the cell wall will still be

relative humidity (RH)

the ratio of the moisture content of the air to the maximum possible moisture content at the same temperature

lose some of its bound water and eventually achieve EMC

if the relative humidity (RH) is less than 100%, the cell wall will

equilibrium moisture content (EMC)

no not loss or gain of moisture

fiber saturation point (FSP)

when the lumen contains no free water, but the cell walls are still fully saturated (only bound water)

capillary action

tendency of water to rise in a narrow space due to cohesion, adhesion, and surface tension; the smaller diameter of the capillary, the higher the water rises

water potential gradient

water moves from a locus of higher water potential to one of lower water potential

absorption

the process by which water is taken up into the physical structure of the tree

pits and perforation plates

how water moves from cell to cell up the tree

permeability

the rate of flow of liquids and gasses through xylem; heaviliy dependent on size of openings between cells (size of margo), much greater in longitudinal direction

reduced permeability

extractives, occlusions (tyloses), aspirated pits

adsorption

the process of binding or sticking to a surface; the amount of accessible OH groups for water molecules to create hydrogen bonds

amporphous regions

areas where most hydrogen bonding occurs; where water 'looks' for to attach to open OH/hydroxyl groups

diffusion

movement of molecules from an area of higher concentration to an area of lower concentration; driven by a moisture gradient in the wood -- moving water from the wetter center to the dryer surface wood

hysteresis

the lag between EMC and desorption and adsorption; the period between when hydrogen bonds occur -- when water molecules are finding OH groups to bind to

no impact on volume

addition or loss of free water has

shrinkage

loss of bound water

swelling

addition of bound water

swelling and shrinking

occurs mostly in tangential and radial directions

cause of shrinking and swelling

water molecules absorb to cellulose or hemicellulose molecules in the cell wall, pushing them apart in the process, increasing distance and causing dimensional change (vice versa for shrinkage)

S2

contributes most to shrinking and swelling due to its thickness; it's microfibril angle is almost completely vertical, so when cellulose molecules are pushed apart, swelling is in a lateral direction

lumen size in shrinking and swelling

stays constant; volumetric change is in the cell wall only

proportional to the amount of water los tor gained

the amount of shrinking or swelling done is

denser species

shrink and swell more, as they contain more wood (more cellulose, more molecules to push apart, etc)

double in the tangential direction

shrinkage is about

latewood

swells and shrinks more because it contains more cellulose; it dominates the tangential direction

irregular wood

reaction wood (compression and tension), juvenile wood, special figure, monocot

reaction wood

develops in leaning trees and most branches; a tree's physiological mechanism for redirecting growth to vertical -- compression wood and tension wood

compression wood

softwoods, on the lower side of a leaning stem; wide growth rings, thicker latewood, irregularly shaped stem with off-center pith common

compression wood microscopically

round tracheids, intercellular spaces, thicker and denser cell walls that have a greater proportion of lignin, spiral cavities, large microfibril angle (less vertical)

compression wood properties

denser, more brittle, more longitudinal shrinkage and swelling, can cause warp and twist

tension wood

hardwoods, upper side of a leaning stem or branch

tension wood microscopically

gelatinous fibers (usually in earlywood), greater proportion of cellulose than normal wood

tension wood properties

denser, strength problems, fuzzy grain, often 'silvery' appearance, greater longitudinal shrinkage and swelling, can cause warp and twist

juvenile wood

occurs in the first few growth rings surrounding the pith, develops within the first 1-15 years

juvenile wood macroscopically

often wide growth rings near pith, needle traces common

juvenile wood microscopically

shorter wood cells than mature wood, fewer latewood cells, microfibril angle of secondary wall is greater (less vertical)

juvenile wood properties

less dense, greater longitudinal shrinkage and swelling, warp and twist common, low strength, unpredictable

special figure

uncommon patterns or markings on longitudinal surfaces, often considered beautiful and/or valuable, used for decorative purposes; pigment figure, figure caused by irregular growth rings, figure caused by deviation in cell or grain direction

pigment figure

pigmented areas of the heartwood might not concentric with the growth rings

figure from irregular growth rings

caused by fluted, indented, furrowed rings, etc; can cause bear scratches, dimples, birds eye figure, blister figure

figure from deviation in grain or cell orientation

interlocked grain (striped figure), wavy grain (curly figure), bud formations (burls)

monocots

non-dicot angiosperms; bamboos, palm trees, rattan, yucca, etc

monocot properties

vascular cells arranged in bundles (instead of ring arrangements) and are surrounded by ground tissue (parenchyma cells); fibrovascular bundles contain vessels, fibers, phloem cells

medium to low

soft pine density

gradual EW/LW transition

soft pines have

exhibit dimples

lodgepole pine and ponderosa pine

exhibit conspicuous resin canals on longitudinal surfaces

sugar pine and eastern white pine

earlywood to latewood transition

you can differentiate hard pines from soft pines by their

dentate ray tracheids

hard pines always exhibit

fenestriform pitting

soft pines always have

occasionally has 3+ bordered pits

baldcypress and redwood

has abrupt transition from EW to LW

douglas-fir, redwood, western larch, baldcypress

distinct color difference between sapwood and heartwood

redwood, douglas-fir, larch

higher density, more purplish-brown color, finer texture

eastern redcedar has a

abrupt transition to EW/LW

western redcedar