HARDWOOD STRUCTURE

Hardwood xylem (wood) is composed of at least 4 major kinds of cells; each of which may constitute 15% or more of the volume (see Table 5.1. on Page 82 of Textbook).

Hardwoods contain vessels -- softwoods do not.

Hardwood rays may contain 1 to 30 cells in width
        average volume is 17% of the xylem - can be more than 30% 
        rays are seldom in a straight line.

LONGITUDINAL CELLS

VESSEL ELEMENTS

specialized conducting cells -- much larger in diameter than other cell types

                see Figure 5.4 on Page 89 in Textbook

Arrangements:

        ring porous -- large vessels in earlywood -- small vessels in latewood

        diffuse porous -- medium vessels throughout

Vessels are an end to end arrangement of vessel elements with end perforation plates between elements. There are three types of perforation plates: Simple,  Scalariform, and Foraminate.

        see Figure 5.6 on Page 92 in textbook.

Vessel to vessel pitting is many bordered pits -- arrangement differs between species: Alternate, Opposite, and Scalariform. 
        see Figure 5.8 on Page 93 in Textbook

Vessels form pits with other cells except fiber tracheids.

TYLOSES

A. vessels die and dry up

B. enzymines dissolve pit membrane

C. parenchyma cytoplasm expands into vessel -- looks like a balloon

Some hardwoods have tyloses and are impenetrable.

Some hardwoods have no tyloses and are easily penetrated.

        see Figure 5.11 on Page 95 in Textbook.

LONGITUDINAL PARENCHYMA

A. thin-walled storage units usually divided into number of smaller cells by crosswalls during maturation

B. brick shaped epithelium around gum canals

C. in some domestic hardwoods -- up to 24 % volume are longitudinal parenchyma

D. they make up definite patterns that are visible to the naked eye and can be used for identification.

FIBERS -- FIBER TRACHEIDS

A. long -- though less than 1 mm  --  see Figure 5.4 on Page 89 in Textbook.

B. Round

C. Tapered

D. Usually thick walled

E. Main function is mechanical support

F. pits -- bordered with less developed borders -- except libriform fibers have simple pits.

VASCULAR TRACHEIDS

shaped like vessels but has bordered pits on the ends

VASICENTRIC TRACHEIDS

like parenchyma but with bordered pits

RAYS

cell types:

A. procumbent -- square or rectangular arranged horizontally

B. Upright -- long axis parallel to grain -- located on upper or lower ray margins

a few hardwood species have uniseriate rays; but most have rays with up to 30 cells wide.

STORIED STRUCTURES

tangentially oriented tiers usually ray cells but can be other cell types.